feat(surface): major work on implementing surface constraints in a presciption agnostic manner

CMakeLists.txt

@@ -1,5 +1,5 @@
 cmake_minimum_required(VERSION 3.28)
-project(MeanField CXX)
+project(MeanField C CXX)
 
 set(CMAKE_CXX_STANDARD 23)
 set(CMAKE_CXX_STANDARD_REQUIRED ON)
@@ -138,15 +138,24 @@ target_sources(mean_field
         libmeanfield/interface/operators/kernels/rotation_displacement_force_kernels.cppm
         libmeanfield/interface/operators/prepared_rotation_displacement_force.cppm
         libmeanfield/interface/operators/prepared_displacement_operator.cppm
-        libmeanfield/interface/eos/eos_base.cppm
+        libmeanfield/interface/eos/quantities.cppm
+        libmeanfield/interface/eos/relations.cppm
+        libmeanfield/interface/eos/concepts.cppm
+        libmeanfield/interface/eos/evaluation.cppm
+        libmeanfield/interface/eos/pressure_surface.cppm
+        libmeanfield/interface/eos/runtime.cppm
         libmeanfield/interface/eos/polytropic.cppm
         libmeanfield/interface/models/structure/structure_base.cppm
         libmeanfield/interface/models/structure/polytropic.cppm
         libmeanfield/interface/models/structure_profile.cppm
-        libmeanfield/interface/surface/surface_base.cppm
-        libmeanfield/interface/surface/isobaric.cppm
+        libmeanfield/interface/surface/constant.cppm
+        libmeanfield/interface/surface/dependencies.cppm
+        libmeanfield/interface/surface/compiled.cppm
+        libmeanfield/interface/surface/compiler.cppm
         libmeanfield/interface/models/stellar_model.cppm
         libmeanfield/interface/operators/prepared_mass_normalization.cppm
+        libmeanfield/interface/operators/prepared_centering_constraint.cppm
+        libmeanfield/interface/operators/prepared_surface_constraint.cppm
         libmeanfield/interface/operators/prepared_stellar_equilibrium.cppm
 )
 
@@ -194,6 +203,12 @@ add_executable(tests
         tests/operators/contexts/gravity_field_context.cpp
         tests/physics/gravity_monopole_accuracy.cpp
         tests/physics/barotrope.cpp
+        tests/physics/polytropic_eos_characterization.cpp
+        tests/physics/equation_of_state_type_system.cpp
+        tests/physics/equation_of_state_consumer_contracts.cpp
+        tests/physics/polytropic_eos_relations.cpp
+        tests/physics/equation_of_state_runtime_view.cpp
+        tests/surface/constant_surface_compilation.cpp
         tests/operators/kernels/barotropic_closure_kernels.cpp
         tests/operators/prepared_barotropic_closure.cpp
         tests/operators/contexts/barotropic_closure_linearization_context.cpp
@@ -215,7 +230,6 @@ add_executable(tests
         tests/operators/prepared_rotation_displacement_force_analytic.cpp
         tests/operators/prepared_rotation_displacement_force_affine_deformation.cpp
         tests/operators/prepared_displacement_operator.cpp
-        tests/surface/isobaric.cpp
         tests/models/stellar_model.cpp
         tests/operators/prepared_mass_normalization.cpp
         tests/operators/prepared_stellar_equilibrium.cpp
@@ -233,6 +247,7 @@ target_sources(experiment_mod
         PUBLIC
         FILE_SET CXX_MODULES FILES
         experiments/experiment_results.cppm
+        experiments/stellar_null_space.cppm
 )
 target_link_libraries(experiment_mod
         PUBLIC
@@ -247,6 +262,21 @@ add_executable(experiments
 
 target_link_libraries(experiments PRIVATE mean_field test_mod experiment_mod Catch2::Catch2 Boost::boost)
 
+add_executable(stellar_null_space_experiments
+        experiments/experiment_main.cpp
+        experiments/rigid_motion_null_space.cpp
+        experiments/gravity_completed_rigid_motion.cpp
+)
+
+target_link_libraries(stellar_null_space_experiments
+        PRIVATE
+        mean_field
+        test_mod
+        experiment_mod
+        Catch2::Catch2
+        Boost::boost
+)
+
 include (CTest)
 include (Catch)
 catch_discover_tests(

experiments/README.md

@@ -24,6 +24,49 @@ Run only the budget and choose its output path with:
 ./mean_field_experiments --experiment-output gravity_budget.csv --catch2 "[accuracy]"
 ```
 
+## Stellar-equilibrium null-space experiments
+
+`stellar_null_space_experiments` is a dedicated diagnostic executable rather
+than an ordinary verification or validation test. It constructs the analytic
+`n = 3` Lane-Emden seed, probes the three computational translations and three
+computational rotations, and compares the Jacobian before and after the strong
+centering-row replacement. It records total and residual-block response norms,
+the isolated centering contribution, and centered finite-difference errors.
+
+The experiment prints rank-zero progress messages while it builds the seed,
+solves its gravity field, and completes each rigid-mode case. Run it with:
+
+```text
+mpirun -np 1 ./cmake-build-debug-homebrew/stellar_null_space_experiments \
+    --experiment-output stellar_null_space.csv \
+    --catch2 "[null_space][rigid_motion]"
+```
+
+The rotation sweep includes zero rotation and a spherical-state diagnostic at
+half the Keplerian angular speed. The rotating result is an operator-symmetry
+probe, not a definitive rotating-equilibrium null-space measurement.
+
+The gravity-completed probe solves the linearized mixed gravity subsystem for
+the gravity-gradient and gravity-potential variations accompanying each rigid
+displacement. It then measures the complete equilibrium response with and
+without the centering rows:
+
+```text
+mpirun -np 1 ./cmake-build-debug-homebrew/stellar_null_space_experiments \
+    --experiment-output gravity_completed_null_space.csv \
+    --catch2 "[null_space][gravity_completed]"
+```
+
+The gravity solver prints its convergence summary, while the experiment prints
+the current mode and completed-case count. This probe prepares each rotation
+state only once and does not repeat the expensive nonlinear finite-difference
+calculations from the original rigid-motion diagnostic.
+
+A whole-Jacobian dense singular-value experiment is intentionally deferred.
+The checked-in `sandbox.smesh` is too large for a useful dense SVD, and the
+current matrix-free root operator does not provide a transpose action needed by
+a scalable smallest-singular-value method.
+
 The executable needs the same dependencies, generated module mapping, and
 configuration registration as the existing Catch2 test executable. Add
 `experiment_main.cpp` and `gravity_accuracy_budget.cpp` as a second executable

experiments/gravity_completed_rigid_motion.cpp

@@ -0,0 +1,273 @@
+#include <catch2/catch_test_macros.hpp>
+
+#include <algorithm>
+#include <array>
+#include <cmath>
+#include <limits>
+#include <map>
+#include <string>
+
+#include <mfem.hpp>
+#include <mpi.h>
+
+import experiment;
+import experiment.stellar_null_space;
+import mean_field;
+import test_helpers;
+
+namespace {
+    class GravityUnknownJacobian final : public mfem::Operator {
+    public:
+        explicit GravityUnknownJacobian(
+            const mean_field::operators::PreparedStellarEquilibriumOperator &stellarOperator
+        )
+            : mfem::Operator(
+                  stellarOperator.GetLayout().size(experiment::null_space::gravityGradientValue) +
+                  stellarOperator.GetLayout().size(experiment::null_space::gravityPotentialValue)
+              ),
+              m_stellarOperator(stellarOperator),
+              m_gravityGradientSize(stellarOperator.GetLayout().size(experiment::null_space::gravityGradientValue)) {
+            MFEM_VERIFY(Width() == Height(), "The reduced gravity Jacobian must be square.");
+        }
+
+        void Mult(
+            const mfem::Vector &gravityDirection,
+            mfem::Vector &gravityAction
+        ) const override {
+            MFEM_VERIFY(gravityDirection.Size() == Width(), "The reduced gravity direction has the wrong size.");
+
+            const mfem::Vector gravityGradientDirection(
+                const_cast<mfem::real_t *>(gravityDirection.GetData()), m_gravityGradientSize
+            );
+            const mfem::Vector gravityPotentialDirection(
+                const_cast<mfem::real_t *>(gravityDirection.GetData()) + m_gravityGradientSize,
+                Width() - m_gravityGradientSize
+            );
+
+            m_stellarOperator.GetGravityOperator().ApplyGravityUnknowns(
+                gravityGradientDirection,
+                gravityPotentialDirection,
+                m_stellarOperator.GetGravityContext().GetGeometryContext(),
+                gravityAction
+            );
+        }
+
+        [[nodiscard]] int gravity_gradient_size() const noexcept {
+            return m_gravityGradientSize;
+        }
+
+    private:
+        const mean_field::operators::PreparedStellarEquilibriumOperator &m_stellarOperator;
+        int m_gravityGradientSize;
+    };
+
+    void add_block_metrics(
+        std::map<
+            std::string,
+            double> &metrics,
+        const std::string &prefix,
+        const std::array<
+            double,
+            6> &norms
+    ) {
+        for (std::size_t block = 0; block < norms.size(); ++block) {
+            metrics.emplace(prefix + experiment::null_space::residualBlockNames[block] + "_norm", norms[block]);
+        }
+    }
+
+    [[nodiscard]] mfem::Vector gravity_residual_blocks(
+        const mfem::Vector &completeAction,
+        const mean_field::operators::StellarEquilibriumLayout &layout
+    ) {
+        const mfem::Vector gradient = experiment::null_space::const_residual_view(
+            completeAction, layout, experiment::null_space::gravityGradientResidual
+        );
+        const mfem::Vector potential = experiment::null_space::const_residual_view(
+            completeAction, layout, experiment::null_space::gravityPotentialResidual
+        );
+
+        mfem::Vector result(gradient.Size() + potential.Size());
+        mfem::Vector(result.GetData(), gradient.Size())                    = gradient;
+        mfem::Vector(result.GetData() + gradient.Size(), potential.Size()) = potential;
+        return result;
+    }
+
+    void assign_gravity_completion(
+        mfem::Vector &completeDirection,
+        const mean_field::operators::StellarEquilibriumLayout &layout,
+        const mfem::Vector &gravityCompletion,
+        const int gravityGradientSize
+    ) {
+        const mfem::Vector gravityGradient(
+            const_cast<mfem::real_t *>(gravityCompletion.GetData()), gravityGradientSize
+        );
+        const mfem::Vector gravityPotential(
+            const_cast<mfem::real_t *>(gravityCompletion.GetData()) + gravityGradientSize,
+            gravityCompletion.Size() - gravityGradientSize
+        );
+        experiment::null_space::assign_value_block(
+            completeDirection, layout, experiment::null_space::gravityGradientValue, gravityGradient
+        );
+        experiment::null_space::assign_value_block(
+            completeDirection, layout, experiment::null_space::gravityPotentialValue, gravityPotential
+        );
+    }
+
+    void apply_centering_rows(
+        const mean_field::operators::PreparedStellarEquilibriumOperator &stellarOperator,
+        const mfem::Vector &direction,
+        mfem::Vector &action
+    ) {
+        const auto &layout = stellarOperator.GetLayout();
+        const mfem::Vector displacementDirection =
+            experiment::null_space::const_value_view(direction, layout, experiment::null_space::displacementValue);
+        mfem::Vector displacementAction =
+            experiment::null_space::residual_view(action, layout, experiment::null_space::displacementResidual);
+        stellarOperator.GetCenteringConstraintOperator().ApplyJacobianRows(displacementDirection, displacementAction);
+    }
+} // namespace
+
+TEST_CASE(
+    "Gravity-Completed Rigid Motion Responses Of The Stellar Equilibrium Jacobian",
+    "[null_space][gravity_completed]"
+) {
+    mean_field::utils::Args args = test_utils::setup_args();
+    args.p.rtol                  = 1.0e-11;
+    args.p.atol                  = std::min(args.p.atol, 1.0e-13);
+    args.p.max_iters             = std::max(args.p.max_iters, 2000);
+
+    experiment::null_space::N3Equilibrium fixture(std::move(args));
+    const MPI_Comm communicator = fixture.fem().mesh->GetComm();
+    int rank                    = 0;
+    MPI_Comm_rank(communicator, &rank);
+
+    const auto modes = experiment::null_space::make_rigid_modes(fixture);
+    constexpr std::array<double, 2> rotationFractions{0.0, 0.5};
+    const int totalCases = static_cast<int>(rotationFractions.size() * modes.size());
+    int completedCases   = 0;
+
+    for (const double rotationFraction : rotationFractions) {
+        const mean_field::physics::RigidRotation rotation = fixture.rotation(rotationFraction);
+        fixture.prepare(fixture.state(), rotation);
+
+        GravityUnknownJacobian gravityUnknownJacobian(fixture.stellar_operator());
+        mean_field::operators::ReducedGravityFieldPreconditioner gravityPreconditioner(
+            fixture.fem(), fixture.stellar_operator().GetGravityContext().GetGeometryContext()
+        );
+
+        mfem::MINRESSolver gravitySolver(communicator);
+        gravitySolver.SetOperator(gravityUnknownJacobian);
+        gravitySolver.SetPreconditioner(gravityPreconditioner);
+        gravitySolver.SetRelTol(1.0e-11);
+        gravitySolver.SetAbsTol(1.0e-13);
+        gravitySolver.SetMaxIter(2000);
+        gravitySolver.SetPrintLevel(1);
+
+        for (const experiment::null_space::RigidMode &mode : modes) {
+            experiment::null_space::report_progress(
+                communicator, "solving the gravity completion for " + mode.name + " at rotation fraction " +
+                                  std::to_string(rotationFraction) + " (" + std::to_string(completedCases + 1) + "/" +
+                                  std::to_string(totalCases) + ")"
+            );
+
+            const mfem::Vector displacementOnlyAction = fixture.unpinned_jacobian_action(mode.direction);
+            mfem::Vector gravityRightHandSide =
+                gravity_residual_blocks(displacementOnlyAction, fixture.stellar_operator().GetLayout());
+            gravityRightHandSide *= -1.0;
+
+            mfem::Vector gravityCompletion(gravityUnknownJacobian.Width());
+            gravityCompletion = 0.0;
+            gravitySolver.Mult(gravityRightHandSide, gravityCompletion);
+
+            REQUIRE(gravitySolver.GetConverged());
+
+            mfem::Vector gravitySolveAction;
+            gravityUnknownJacobian.Mult(gravityCompletion, gravitySolveAction);
+            mfem::Vector gravitySolveResidual(gravitySolveAction);
+            gravitySolveResidual -= gravityRightHandSide;
+
+            const double gravityRightHandSideNorm =
+                experiment::null_space::global_norm(gravityRightHandSide, communicator);
+            const double gravitySolveResidualNorm =
+                experiment::null_space::global_norm(gravitySolveResidual, communicator);
+            const double gravitySolveRelativeResidual =
+                gravitySolveResidualNorm / std::max(gravityRightHandSideNorm, std::numeric_limits<double>::epsilon());
+
+            REQUIRE(std::isfinite(gravitySolveRelativeResidual));
+
+            mfem::Vector completedDirection(mode.direction);
+            assign_gravity_completion(
+                completedDirection, fixture.stellar_operator().GetLayout(), gravityCompletion,
+                gravityUnknownJacobian.gravity_gradient_size()
+            );
+
+            const mfem::Vector completedUnpinnedAction = fixture.unpinned_jacobian_action(completedDirection);
+            mfem::Vector completedConstrainedAction(completedUnpinnedAction);
+            apply_centering_rows(fixture.stellar_operator(), completedDirection, completedConstrainedAction);
+
+            mfem::Vector centeringContribution(completedConstrainedAction);
+            centeringContribution -= completedUnpinnedAction;
+
+            std::map<std::string, double> metrics{
+                {"displacement_only_input_norm", experiment::null_space::global_norm(mode.direction, communicator)},
+                {"gravity_completion_norm", experiment::null_space::global_norm(gravityCompletion, communicator)},
+                {"completed_input_norm", experiment::null_space::global_norm(completedDirection, communicator)},
+                {"displacement_only_action_norm",
+                 experiment::null_space::global_norm(displacementOnlyAction, communicator)},
+                {"gravity_completed_unpinned_action_norm",
+                 experiment::null_space::global_norm(completedUnpinnedAction, communicator)},
+                {"gravity_completed_constrained_action_norm",
+                 experiment::null_space::global_norm(completedConstrainedAction, communicator)},
+                {"centering_contribution_norm",
+                 experiment::null_space::global_norm(centeringContribution, communicator)},
+                {"gravity_solve_rhs_norm", gravityRightHandSideNorm},
+                {"gravity_solve_residual_norm", gravitySolveResidualNorm},
+                {"gravity_solve_relative_residual", gravitySolveRelativeResidual},
+                {"gravity_solve_iterations", static_cast<double>(gravitySolver.GetNumIterations())},
+                {"gravity_solve_final_norm", gravitySolver.GetFinalNorm()}
+            };
+
+            add_block_metrics(
+                metrics, "displacement_only_",
+                experiment::null_space::residual_block_norms(
+                    displacementOnlyAction, fixture.stellar_operator().GetLayout(), communicator
+                )
+            );
+            add_block_metrics(
+                metrics, "gravity_completed_unpinned_",
+                experiment::null_space::residual_block_norms(
+                    completedUnpinnedAction, fixture.stellar_operator().GetLayout(), communicator
+                )
+            );
+            add_block_metrics(
+                metrics, "gravity_completed_constrained_",
+                experiment::null_space::residual_block_norms(
+                    completedConstrainedAction, fixture.stellar_operator().GetLayout(), communicator
+                )
+            );
+
+            if (rank == 0) {
+                experiment::record_experiment_result(
+                    "gravity_completed_stellar_rigid_motion_null_space", mode.name,
+                    {{"mode_kind",
+                      mode.kind == experiment::null_space::RigidModeKind::translation ? "translation" : "rotation"},
+                     {"axis", std::to_string(mode.axis)},
+                     {"rotation_fraction_of_keplerian", std::to_string(rotationFraction)},
+                     {"mesh_file", test_utils::setup_args().mesh_file},
+                     {"local_state_dofs", std::to_string(fixture.stellar_operator().Width())}},
+                    std::move(metrics)
+                );
+            }
+
+            ++completedCases;
+            experiment::null_space::report_progress(
+                communicator, "completed " + std::to_string(completedCases) + "/" + std::to_string(totalCases) +
+                                  " gravity-completed rigid-mode cases"
+            );
+        }
+    }
+
+    experiment::null_space::report_progress(
+        communicator, "gravity-completed rigid-motion probe complete; writing CSV output"
+    );
+}

experiments/rigid_motion_null_space.cpp

@@ -0,0 +1,174 @@
+#include <catch2/catch_test_macros.hpp>
+
+#include <algorithm>
+#include <array>
+#include <cmath>
+#include <limits>
+#include <map>
+#include <string>
+
+#include <mfem.hpp>
+#include <mpi.h>
+
+import experiment;
+import experiment.stellar_null_space;
+import mean_field;
+import test_helpers;
+
+namespace {
+    [[nodiscard]] double relative_difference(
+        const mfem::Vector &computed,
+        const mfem::Vector &reference,
+        const MPI_Comm communicator
+    ) {
+        mfem::Vector difference(computed);
+        difference -= reference;
+        const double scale = std::max(
+            {experiment::null_space::global_norm(computed, communicator),
+             experiment::null_space::global_norm(reference, communicator), std::numeric_limits<double>::epsilon()}
+        );
+        return experiment::null_space::global_norm(difference, communicator) / scale;
+    }
+
+    void add_block_metrics(
+        std::map<
+            std::string,
+            double> &metrics,
+        const std::string &prefix,
+        const std::array<
+            double,
+            6> &norms
+    ) {
+        for (std::size_t block = 0; block < norms.size(); ++block) {
+            metrics.emplace(prefix + experiment::null_space::residualBlockNames[block] + "_norm", norms[block]);
+        }
+    }
+} // namespace
+
+TEST_CASE(
+    "Rigid Motion Responses Of The Stellar Equilibrium Jacobian",
+    "[null_space][rigid_motion]"
+) {
+    mean_field::utils::Args args = test_utils::setup_args();
+    args.p.rtol                  = 1.0e-12;
+    args.p.atol                  = std::min(args.p.atol, 1.0e-14);
+    args.p.max_iters             = std::max(args.p.max_iters, 2000);
+
+    experiment::null_space::N3Equilibrium fixture(std::move(args));
+    const MPI_Comm communicator = fixture.fem().mesh->GetComm();
+    int rank                    = 0;
+    MPI_Comm_rank(communicator, &rank);
+
+    const auto modes = experiment::null_space::make_rigid_modes(fixture);
+    constexpr std::array<double, 2> rotationFractions{0.0, 0.5};
+    constexpr std::array<double, 2> finiteDifferenceSteps{1.0e-4, 1.0e-6};
+    const int totalCases = static_cast<int>(rotationFractions.size() * modes.size());
+    int completedCases   = 0;
+
+    for (const double rotationFraction : rotationFractions) {
+        const mean_field::physics::RigidRotation rotation = fixture.rotation(rotationFraction);
+        fixture.prepare(fixture.state(), rotation);
+
+        mfem::Vector constrainedResidual;
+        fixture.stellar_operator().BuildResidual(constrainedResidual);
+        const mfem::Vector unpinnedResidual = fixture.unpinned_residual();
+
+        REQUIRE(constrainedResidual.Size() == unpinnedResidual.Size());
+        REQUIRE(std::isfinite(experiment::null_space::global_norm(constrainedResidual, communicator)));
+        REQUIRE(std::isfinite(experiment::null_space::global_norm(unpinnedResidual, communicator)));
+
+        for (const experiment::null_space::RigidMode &mode : modes) {
+            experiment::null_space::report_progress(
+                communicator, "probing " + mode.name + " at rotation fraction " + std::to_string(rotationFraction) +
+                                  " (" + std::to_string(completedCases + 1) + "/" + std::to_string(totalCases) + ")"
+            );
+
+            fixture.prepare(fixture.state(), rotation);
+            const mfem::Vector unpinnedAction = fixture.unpinned_jacobian_action(mode.direction);
+            mfem::Vector constrainedAction;
+            fixture.stellar_operator().Mult(mode.direction, constrainedAction);
+
+            mfem::Vector centeringContribution(constrainedAction);
+            centeringContribution -= unpinnedAction;
+
+            const double inputNorm       = experiment::null_space::global_norm(mode.direction, communicator);
+            const double unpinnedNorm    = experiment::null_space::global_norm(unpinnedAction, communicator);
+            const double constrainedNorm = experiment::null_space::global_norm(constrainedAction, communicator);
+
+            REQUIRE(inputNorm > 0.0);
+            REQUIRE(std::isfinite(unpinnedNorm));
+            REQUIRE(std::isfinite(constrainedNorm));
+
+            std::map<std::string, double> metrics{
+                {"input_algebraic_norm", inputNorm},
+                {"unpinned_action_norm", unpinnedNorm},
+                {"unpinned_action_per_input_norm", unpinnedNorm / inputNorm},
+                {"constrained_action_norm", constrainedNorm},
+                {"constrained_action_per_input_norm", constrainedNorm / inputNorm},
+                {"centering_contribution_norm",
+                 experiment::null_space::global_norm(centeringContribution, communicator)},
+                {"unpinned_base_residual_norm", experiment::null_space::global_norm(unpinnedResidual, communicator)},
+                {"constrained_base_residual_norm",
+                 experiment::null_space::global_norm(constrainedResidual, communicator)}
+            };
+
+            add_block_metrics(
+                metrics, "unpinned_",
+                experiment::null_space::residual_block_norms(
+                    unpinnedAction, fixture.stellar_operator().GetLayout(), communicator
+                )
+            );
+            add_block_metrics(
+                metrics, "constrained_",
+                experiment::null_space::residual_block_norms(
+                    constrainedAction, fixture.stellar_operator().GetLayout(), communicator
+                )
+            );
+
+            for (const double step : finiteDifferenceSteps) {
+                mfem::Vector plusState(fixture.state());
+                plusState.Add(step, mode.direction);
+                fixture.prepare(plusState, rotation);
+                const mfem::Vector plusResidual = fixture.unpinned_residual();
+
+                mfem::Vector minusState(fixture.state());
+                minusState.Add(-step, mode.direction);
+                fixture.prepare(minusState, rotation);
+                const mfem::Vector minusResidual = fixture.unpinned_residual();
+
+                mfem::Vector finiteDifference(plusResidual);
+                finiteDifference -= minusResidual;
+                finiteDifference /= 2.0 * step;
+
+                const std::string stepName = step == finiteDifferenceSteps.front() ? "1e-4" : "1e-6";
+                metrics.emplace(
+                    "finite_difference_relative_error_" + stepName,
+                    relative_difference(unpinnedAction, finiteDifference, communicator)
+                );
+            }
+
+            fixture.prepare(fixture.state(), rotation);
+
+            if (rank == 0) {
+                experiment::record_experiment_result(
+                    "stellar_rigid_motion_null_space", mode.name,
+                    {{"mode_kind",
+                      mode.kind == experiment::null_space::RigidModeKind::translation ? "translation" : "rotation"},
+                     {"axis", std::to_string(mode.axis)},
+                     {"rotation_fraction_of_keplerian", std::to_string(rotationFraction)},
+                     {"mesh_file", test_utils::setup_args().mesh_file},
+                     {"local_state_dofs", std::to_string(fixture.stellar_operator().Width())}},
+                    std::move(metrics)
+                );
+            }
+
+            ++completedCases;
+            experiment::null_space::report_progress(
+                communicator,
+                "completed " + std::to_string(completedCases) + "/" + std::to_string(totalCases) + " rigid-mode cases"
+            );
+        }
+    }
+
+    experiment::null_space::report_progress(communicator, "rigid-motion probe complete; writing CSV output");
+}

experiments/stellar_null_space.cppm

@@ -0,0 +1,519 @@
+module;
+
+#include <algorithm>
+#include <array>
+#include <cmath>
+#include <cstdint>
+#include <iostream>
+#include <limits>
+#include <string>
+#include <utility>
+
+#include <mfem.hpp>
+#include <mpi.h>
+
+export module experiment.stellar_null_space;
+
+import mean_field;
+import test_helpers;
+
+export namespace experiment::null_space {
+    using Form         = mean_field::utils::blocks::barotropic_equilibrium_form;
+    using DomainSchema = mean_field::utils::domain::CoreEnvelopeVacuumDomainSchema;
+    using Model        = mean_field::models::StellarModel<mean_field::models::structure::PolytropicStructure>;
+
+    constexpr auto densityValue =
+        mean_field::utils::blocks::get_value_block<Form>(mean_field::utils::blocks::density_field.mass_term);
+    constexpr auto displacementValue =
+        mean_field::utils::blocks::get_value_block<Form>(mean_field::utils::blocks::displacement_field.geometry_term);
+    constexpr auto gravityGradientValue =
+        mean_field::utils::blocks::get_value_block<Form>(mean_field::utils::blocks::gravity_field.gradient_term);
+    constexpr auto gravityPotentialValue =
+        mean_field::utils::blocks::get_value_block<Form>(mean_field::utils::blocks::gravity_field.poisson_term);
+    constexpr auto enthalpyValue =
+        mean_field::utils::blocks::get_value_block<Form>(mean_field::utils::blocks::enthalpy_field.specific_term);
+    constexpr auto bernoulliValue = mean_field::utils::blocks::get_value_block<Form>(
+        mean_field::utils::blocks::barotropic_constant_field.mass_normalization_term
+    );
+
+    constexpr auto gravityGradientResidual =
+        mean_field::utils::blocks::get_residual_block<Form>(mean_field::utils::blocks::gravity_field.gradient_term);
+    constexpr auto gravityPotentialResidual =
+        mean_field::utils::blocks::get_residual_block<Form>(mean_field::utils::blocks::gravity_field.poisson_term);
+    constexpr auto densityResidual =
+        mean_field::utils::blocks::get_residual_block<Form>(mean_field::utils::blocks::density_field.mass_term);
+    constexpr auto displacementResidual = mean_field::utils::blocks::get_residual_block<Form>(
+        mean_field::utils::blocks::displacement_field.geometry_term
+    );
+    constexpr auto enthalpyResidual =
+        mean_field::utils::blocks::get_residual_block<Form>(mean_field::utils::blocks::enthalpy_field.specific_term);
+    constexpr auto massResidual = mean_field::utils::blocks::get_residual_block<Form>(
+        mean_field::utils::blocks::barotropic_constant_field.mass_normalization_term
+    );
+
+    inline constexpr std::array<const char *, 6> residualBlockNames{"gravity_gradient", "gravity_potential", "closure",
+                                                                    "displacement",     "hydrostatic",       "mass"};
+
+    template <int index>
+    [[nodiscard]] mfem::Vector value_view(
+        mfem::Vector &vector,
+        const mean_field::operators::StellarEquilibriumLayout &layout,
+        const mean_field::utils::blocks::value_block<index> block
+    ) {
+        return mfem::Vector(vector.GetData() + layout.offset(block), layout.size(block));
+    }
+
+    template <int index>
+    [[nodiscard]] mfem::Vector const_value_view(
+        const mfem::Vector &vector,
+        const mean_field::operators::StellarEquilibriumLayout &layout,
+        const mean_field::utils::blocks::value_block<index> block
+    ) {
+        return mfem::Vector(const_cast<mfem::real_t *>(vector.GetData()) + layout.offset(block), layout.size(block));
+    }
+
+    template <int index>
+    [[nodiscard]] mfem::Vector residual_view(
+        mfem::Vector &vector,
+        const mean_field::operators::StellarEquilibriumLayout &layout,
+        const mean_field::utils::blocks::residual_block<index> block
+    ) {
+        return mfem::Vector(vector.GetData() + layout.offset(block), layout.size(block));
+    }
+
+    template <int index>
+    [[nodiscard]] mfem::Vector const_residual_view(
+        const mfem::Vector &vector,
+        const mean_field::operators::StellarEquilibriumLayout &layout,
+        const mean_field::utils::blocks::residual_block<index> block
+    ) {
+        return mfem::Vector(const_cast<mfem::real_t *>(vector.GetData()) + layout.offset(block), layout.size(block));
+    }
+
+    template <int index>
+    void assign_value_block(
+        mfem::Vector &vector,
+        const mean_field::operators::StellarEquilibriumLayout &layout,
+        const mean_field::utils::blocks::value_block<index> block,
+        const mfem::Vector &source
+    ) {
+        MFEM_VERIFY(source.Size() == layout.size(block), "Null-space experiment received a block with the wrong size.");
+        value_view(vector, layout, block) = source;
+    }
+
+    [[nodiscard]] inline double global_norm(
+        const mfem::Vector &vector,
+        const MPI_Comm communicator
+    ) {
+        const double localNormSquared = vector * vector;
+        double globalNormSquared      = 0.0;
+        MPI_Allreduce(&localNormSquared, &globalNormSquared, 1, MPI_DOUBLE, MPI_SUM, communicator);
+        return std::sqrt(globalNormSquared);
+    }
+
+    inline void report_progress(
+        const MPI_Comm communicator,
+        const std::string &message
+    ) {
+        int rank = 0;
+        MPI_Comm_rank(communicator, &rank);
+        if (rank == 0) {
+            std::cout << "[null-space experiment] " << message << std::endl;
+        }
+    }
+
+    [[nodiscard]] inline mean_field::operators::StellarEquilibriumDependencies make_dependencies() {
+        return {
+            .discretization    = {.identity = 2003, .revision = 1},
+            .density           = {.identity = 2011, .revision = 1},
+            .displacement      = {.identity = 2017, .revision = 1},
+            .gravityGradient   = {.identity = 2027, .revision = 1},
+            .gravityPotential  = {.identity = 2029, .revision = 1},
+            .enthalpy          = {.identity = 2039, .revision = 1},
+            .bernoulliConstant = {.identity = 2053, .revision = 1},
+            .rotation          = {.identity = 2063, .revision = 1},
+            .targetMass        = {.identity = 2069, .revision = 1}
+        };
+    }
+
+    inline void increment_state_revisions(mean_field::operators::StellarEquilibriumDependencies &dependencies) {
+        ++dependencies.density.revision;
+        ++dependencies.displacement.revision;
+        ++dependencies.gravityGradient.revision;
+        ++dependencies.gravityPotential.revision;
+        ++dependencies.enthalpy.revision;
+        ++dependencies.bernoulliConstant.revision;
+    }
+
+    [[nodiscard]] inline mfem::Vector pack_gravity_state(
+        const mfem::Vector &density,
+        const mfem::Vector &displacement,
+        const mfem::Vector &gravityGradient,
+        const mfem::Vector &gravityPotential
+    ) {
+        const std::array<int, 5> offsets{
+            0, density.Size(), density.Size() + displacement.Size(),
+            density.Size() + displacement.Size() + gravityGradient.Size(),
+            density.Size() + displacement.Size() + gravityGradient.Size() + gravityPotential.Size()
+        };
+        mfem::Vector packed(offsets.back());
+        mfem::Vector(packed.GetData() + offsets[0], density.Size())          = density;
+        mfem::Vector(packed.GetData() + offsets[1], displacement.Size())     = displacement;
+        mfem::Vector(packed.GetData() + offsets[2], gravityGradient.Size())  = gravityGradient;
+        mfem::Vector(packed.GetData() + offsets[3], gravityPotential.Size()) = gravityPotential;
+        return packed;
+    }
+
+    [[nodiscard]] inline Model make_model() {
+        const double pi                    = std::acos(-1.0);
+        const double targetMass            = mean_field::utils::MASS;
+        constexpr double dimensionlessMass = 2.0182359509662283534;
+        const double polytropicConstant =
+            pi * mean_field::utils::G * std::pow(targetMass / (4.0 * pi * dimensionlessMass), 2.0 / 3.0);
+
+        return Model{
+            mean_field::models::structure::PolytropicStructure{
+                mean_field::eos::Polytrope{3.0, polytropicConstant}, targetMass
+            },
+            mean_field::surface::ConstantPressureSurface{mean_field::eos::PressureValue{0.0}}
+        };
+    }
+
+    class N3Equilibrium final {
+    public:
+        explicit N3Equilibrium(mean_field::utils::Args args)
+            : m_args(std::move(args)),
+              m_fem(
+                  mean_field::fem::setup_fem(
+                      m_args.mesh_file,
+                      m_args,
+                      0
+                  )
+              ),
+              m_model(make_model()),
+              m_operator(
+                  m_fem,
+                  *m_fem.domainMapperStateless,
+                  m_model
+              ),
+              m_state(m_operator.GetLayout().value_offsets().Last()),
+              m_dependencies(make_dependencies()) {
+            MFEM_VERIFY(m_fem.okay(), "The null-space experiment could not construct the finite-element problem.");
+            m_state = 0.0;
+            initialize_state();
+        }
+
+        [[nodiscard]] mean_field::fem::FEM &fem() noexcept {
+            return m_fem;
+        }
+
+        [[nodiscard]] const mean_field::fem::FEM &fem() const noexcept {
+            return m_fem;
+        }
+
+        [[nodiscard]] mean_field::operators::PreparedStellarEquilibriumOperator &stellar_operator() noexcept {
+            return m_operator;
+        }
+
+        [[nodiscard]] const mean_field::operators::PreparedStellarEquilibriumOperator &
+        stellar_operator() const noexcept {
+            return m_operator;
+        }
+
+        [[nodiscard]] const mfem::Vector &state() const noexcept {
+            return m_state;
+        }
+
+        [[nodiscard]] mean_field::physics::RigidRotation rotation(const double fractionOfKeplerian) const {
+            const double radius         = mean_field::utils::RADIUS;
+            const double mass           = mean_field::utils::MASS;
+            const double keplerianSpeed = std::sqrt(mean_field::utils::G * mass / (radius * radius * radius));
+
+            mfem::Vector angularVelocity(3);
+            angularVelocity    = 0.0;
+            angularVelocity(2) = fractionOfKeplerian * keplerianSpeed;
+
+            mfem::Vector center(3);
+            center = 0.0;
+            return mean_field::physics::RigidRotation(angularVelocity, center);
+        }
+
+        void prepare(
+            const mfem::Vector &state,
+            const mean_field::physics::RigidRotation &rotation
+        ) {
+            m_currentState = state;
+            increment_state_revisions(m_dependencies);
+            ++m_dependencies.rotation.revision;
+            m_operator.Prepare(state, m_dependencies, rotation);
+        }
+
+        [[nodiscard]] mfem::Vector unpinned_residual() const {
+            const auto &layout                  = m_operator.GetLayout();
+            const mfem::Vector reducedDensity   = const_value_view(m_currentState, layout, densityValue);
+            const mfem::Vector displacement     = const_value_view(m_currentState, layout, displacementValue);
+            const mfem::Vector gravityGradient  = const_value_view(m_currentState, layout, gravityGradientValue);
+            const mfem::Vector gravityPotential = const_value_view(m_currentState, layout, gravityPotentialValue);
+            const mfem::Vector gravityState =
+                pack_gravity_state(reducedDensity, displacement, gravityGradient, gravityPotential);
+
+            mfem::Vector gravity;
+            mfem::Vector closure;
+            mfem::Vector displacementRows;
+            mfem::Vector hydrostatic;
+            mfem::Vector mass;
+            m_operator.GetGravityOperator().Mult(gravityState, gravity);
+            m_operator.GetBarotropicClosureOperator().BuildResidual(closure);
+            m_operator.GetDisplacementOperator().BuildResidual(displacementRows);
+            m_operator.GetHydrostaticOperator().BuildResidual(hydrostatic);
+            m_operator.GetSurfaceConstraintOperator().ApplyResidualRows(hydrostatic);
+            m_operator.GetMassNormalizationOperator().BuildResidual(mass);
+
+            return pack_residual(gravity, closure, displacementRows, hydrostatic, mass);
+        }
+
+        [[nodiscard]] mfem::Vector unpinned_jacobian_action(const mfem::Vector &direction) const {
+            const auto &layout                           = m_operator.GetLayout();
+            const mfem::Vector reducedDensityDirection   = const_value_view(direction, layout, densityValue);
+            const mfem::Vector displacementDirection     = const_value_view(direction, layout, displacementValue);
+            const mfem::Vector gravityGradientDirection  = const_value_view(direction, layout, gravityGradientValue);
+            const mfem::Vector gravityPotentialDirection = const_value_view(direction, layout, gravityPotentialValue);
+            const mfem::Vector reducedEnthalpyDirection  = const_value_view(direction, layout, enthalpyValue);
+            const mfem::Vector bernoulliDirection        = const_value_view(direction, layout, bernoulliValue);
+
+            const mfem::Vector gravityDirection          = pack_gravity_state(
+                reducedDensityDirection, displacementDirection, gravityGradientDirection, gravityPotentialDirection
+            );
+
+            mfem::Vector gravity;
+            mfem::Vector closure;
+            mfem::Vector displacementRows;
+            mfem::Vector hydrostatic;
+            mfem::Vector mass;
+            m_operator.GetGravityJacobianOperator().Mult(gravityDirection, gravity);
+            m_operator.GetBarotropicClosureOperator().Mult(
+                reducedDensityDirection, reducedEnthalpyDirection, displacementDirection, closure
+            );
+            m_operator.GetDisplacementOperator().ApplyCompleteJacobianAction(
+                reducedDensityDirection, displacementDirection, gravityGradientDirection, reducedEnthalpyDirection,
+                displacementRows
+            );
+            m_operator.GetHydrostaticOperator().ApplyCompleteJacobianAction(
+                reducedEnthalpyDirection, gravityPotentialDirection, bernoulliDirection(0), displacementDirection,
+                hydrostatic
+            );
+            m_operator.GetSurfaceConstraintOperator().ApplyJacobianRows(reducedEnthalpyDirection, hydrostatic);
+            m_operator.GetMassNormalizationOperator().ApplyCompleteJacobianAction(
+                reducedDensityDirection, displacementDirection, mass
+            );
+
+            return pack_residual(gravity, closure, displacementRows, hydrostatic, mass);
+        }
+
+    private:
+        void initialize_state() {
+            report_progress(m_fem.mesh->GetComm(), "constructing the analytic n=3 Lane-Emden state");
+
+            constexpr double surfaceCoordinate = 6.8968486193769603755;
+            constexpr int radialSampleCount    = 8192;
+            const double pi                    = std::acos(-1.0);
+            const double radius                = mean_field::utils::RADIUS;
+            const double targetMass            = mean_field::utils::MASS;
+            constexpr double dimensionlessMass = 2.0182359509662283534;
+            const double polytropicConstant =
+                pi * mean_field::utils::G * std::pow(targetMass / (4.0 * pi * dimensionlessMass), 2.0 / 3.0);
+            const double centralDensity =
+                std::pow(surfaceCoordinate * std::sqrt(polytropicConstant / (pi * mean_field::utils::G)) / radius, 3.0);
+
+            const mean_field::models::structure::StructureSeed seed =
+                m_model.makeInitialSeed({.centralDensity = centralDensity, .radialSampleCount = radialSampleCount});
+
+            const auto interpolate = [](const mfem::Vector &radii, const mfem::Vector &values, const double r) {
+                if (r <= radii(0)) {
+                    return values(0);
+                }
+                const int finalIndex = radii.Size() - 1;
+                if (r >= radii(finalIndex)) {
+                    return values(finalIndex);
+                }
+                int lower = 0;
+                int upper = finalIndex;
+                while (upper - lower > 1) {
+                    const int middle = lower + (upper - lower) / 2;
+                    if (radii(middle) <= r) {
+                        lower = middle;
+                    } else {
+                        upper = middle;
+                    }
+                }
+                const double fraction = (r - radii(lower)) / (radii(upper) - radii(lower));
+                return (1.0 - fraction) * values(lower) + fraction * values(upper);
+            };
+
+            mfem::FunctionCoefficient densityCoefficient([&seed, &interpolate](const mfem::Vector &position) {
+                const double r = position.Norml2();
+                return r >= seed.stellarRadius ? 0.0 : interpolate(seed.radius, seed.density, r);
+            });
+            mfem::FunctionCoefficient enthalpyCoefficient([&seed, &interpolate](const mfem::Vector &position) {
+                const double r = position.Norml2();
+                return r >= seed.stellarRadius ? 0.0 : interpolate(seed.radius, seed.enthalpy, r);
+            });
+
+            mfem::ParGridFunction densityField(m_fem.densityFes.get());
+            mfem::ParGridFunction enthalpyField(m_fem.enthalpyFes.get());
+            mfem::ParGridFunction displacementField(m_fem.displacementFes.get());
+            densityField      = 0.0;
+            enthalpyField     = 0.0;
+            displacementField = 0.0;
+            densityField.ProjectCoefficient(densityCoefficient);
+            enthalpyField.ProjectCoefficient(enthalpyCoefficient);
+            *m_fem.displacement = displacementField;
+
+            report_progress(m_fem.mesh->GetComm(), "solving the gravity field for the seed state");
+            const mean_field::physics::GravitySolution gravity =
+                mean_field::physics::solve_gravity_field(m_fem, m_args, densityField, displacementField);
+
+            mfem::Vector densityTrue;
+            mfem::Vector enthalpyTrue;
+            mfem::Vector displacementTrue;
+            mfem::Vector gravityGradientTrue;
+            mfem::Vector gravityPotentialTrue;
+            densityField.GetTrueDofs(densityTrue);
+            enthalpyField.GetTrueDofs(enthalpyTrue);
+            displacementField.GetTrueDofs(displacementTrue);
+            gravity.gradPhi.GetTrueDofs(gravityGradientTrue);
+            gravity.phi.GetTrueDofs(gravityPotentialTrue);
+
+            const auto &layout = m_operator.GetLayout();
+            const mean_field::field::FieldDofMap densityMap =
+                mean_field::field::make_field_dof_map<mean_field::field::Density, DomainSchema>(*m_fem.densityFes);
+            const mean_field::field::FieldDofMap enthalpyMap =
+                mean_field::field::make_field_dof_map<mean_field::field::Enthalpy, DomainSchema>(*m_fem.enthalpyFes);
+
+            assign_value_block(m_state, layout, densityValue, densityMap.gather(densityTrue));
+            assign_value_block(m_state, layout, displacementValue, displacementTrue);
+            assign_value_block(m_state, layout, gravityGradientValue, gravityGradientTrue);
+            assign_value_block(m_state, layout, gravityPotentialValue, gravityPotentialTrue);
+            assign_value_block(m_state, layout, enthalpyValue, enthalpyMap.gather(enthalpyTrue));
+            value_view(m_state, layout, bernoulliValue)(0) = -mean_field::utils::G * targetMass / radius;
+
+            m_currentState                                 = m_state;
+            prepare(m_state, rotation(0.0));
+            report_progress(m_fem.mesh->GetComm(), "analytic state is prepared");
+        }
+
+        [[nodiscard]] mfem::Vector pack_residual(
+            const mfem::Vector &gravity,
+            const mfem::Vector &closure,
+            const mfem::Vector &displacementRows,
+            const mfem::Vector &hydrostatic,
+            const mfem::Vector &mass
+        ) const {
+            const auto &layout = m_operator.GetLayout();
+            mfem::Vector result(layout.residual_offsets().Last());
+            result = 0.0;
+            const mfem::Vector gravityGradient(gravity.GetData(), layout.size(gravityGradientResidual));
+            const mfem::Vector gravityPotential(
+                gravity.GetData() + layout.size(gravityGradientResidual), layout.size(gravityPotentialResidual)
+            );
+            residual_view(result, layout, gravityGradientResidual)  = gravityGradient;
+            residual_view(result, layout, gravityPotentialResidual) = gravityPotential;
+            residual_view(result, layout, densityResidual)          = closure;
+            residual_view(result, layout, displacementResidual)     = displacementRows;
+            residual_view(result, layout, enthalpyResidual)         = hydrostatic;
+            residual_view(result, layout, massResidual)             = mass;
+            return result;
+        }
+
+        mean_field::utils::Args m_args;
+        mean_field::fem::FEM m_fem;
+        Model m_model;
+        mean_field::operators::PreparedStellarEquilibriumOperator m_operator;
+        mfem::Vector m_state;
+        mfem::Vector m_currentState;
+        mean_field::operators::StellarEquilibriumDependencies m_dependencies;
+    };
+
+    enum class RigidModeKind : std::uint8_t { translation, rotation };
+
+    struct RigidMode final {
+        std::string name;
+        RigidModeKind kind;
+        int axis;
+        mfem::Vector direction;
+    };
+
+    [[nodiscard]] inline std::array<
+        RigidMode,
+        6>
+    make_rigid_modes(const N3Equilibrium &fixture) {
+        const auto &fem    = fixture.fem();
+        const auto &layout = fixture.stellar_operator().GetLayout();
+        std::array<RigidMode, 6> modes;
+
+        for (int axis = 0; axis < 3; ++axis) {
+            mfem::ParGridFunction translation(fem.displacementFes.get());
+            mfem::Vector translationValue(3);
+            translationValue       = 0.0;
+            translationValue(axis) = 1.0;
+            mfem::VectorConstantCoefficient coefficient(translationValue);
+            translation.ProjectCoefficient(coefficient);
+            mfem::Vector translationTrue;
+            translation.GetTrueDofs(translationTrue);
+
+            mfem::Vector direction(layout.value_offsets().Last());
+            direction = 0.0;
+            assign_value_block(direction, layout, displacementValue, translationTrue);
+            modes[axis] = RigidMode{
+                .name      = std::string("translation_") + static_cast<char>('x' + axis),
+                .kind      = RigidModeKind::translation,
+                .axis      = axis,
+                .direction = std::move(direction)
+            };
+        }
+
+        for (int axis = 0; axis < 3; ++axis) {
+            mfem::ParGridFunction rotation(fem.displacementFes.get());
+            mfem::VectorFunctionCoefficient coefficient(3, [axis](const mfem::Vector &position, mfem::Vector &value) {
+                value.SetSize(3);
+                value            = 0.0;
+                const int first  = (axis + 1) % 3;
+                const int second = (axis + 2) % 3;
+                value(first)     = -position(second);
+                value(second)    = position(first);
+            });
+            rotation.ProjectCoefficient(coefficient);
+            mfem::Vector rotationTrue;
+            rotation.GetTrueDofs(rotationTrue);
+
+            mfem::Vector direction(layout.value_offsets().Last());
+            direction = 0.0;
+            assign_value_block(direction, layout, displacementValue, rotationTrue);
+            modes[3 + axis] = RigidMode{
+                .name      = std::string("rotation_") + static_cast<char>('x' + axis),
+                .kind      = RigidModeKind::rotation,
+                .axis      = axis,
+                .direction = std::move(direction)
+            };
+        }
+        return modes;
+    }
+
+    [[nodiscard]] inline std::array<
+        double,
+        6>
+    residual_block_norms(
+        const mfem::Vector &action,
+        const mean_field::operators::StellarEquilibriumLayout &layout,
+        const MPI_Comm communicator
+    ) {
+        return {
+            global_norm(const_residual_view(action, layout, gravityGradientResidual), communicator),
+            global_norm(const_residual_view(action, layout, gravityPotentialResidual), communicator),
+            global_norm(const_residual_view(action, layout, densityResidual), communicator),
+            global_norm(const_residual_view(action, layout, displacementResidual), communicator),
+            global_norm(const_residual_view(action, layout, enthalpyResidual), communicator),
+            global_norm(const_residual_view(action, layout, massResidual), communicator)
+        };
+    }
+} // namespace experiment::null_space

libmeanfield/impl/analysis/integral.cpp

@@ -14,20 +14,23 @@ namespace {
     ) {
         switch (domain) {
         case mean_field::utils::DOMAINS::CORE:
-            return mean_field::utils::domain::make_attribute_marker<
-                mean_field::utils::domain::Core, DomainSchema>(mesh);
+            return mean_field::utils::domain::make_attribute_marker<mean_field::utils::domain::Core, DomainSchema>(
+                mesh
+            );
         case mean_field::utils::DOMAINS::ENVELOPE:
-            return mean_field::utils::domain::make_attribute_marker<
-                mean_field::utils::domain::Envelope, DomainSchema>(mesh);
+            return mean_field::utils::domain::make_attribute_marker<mean_field::utils::domain::Envelope, DomainSchema>(
+                mesh
+            );
         case mean_field::utils::DOMAINS::ALL:
-            return mean_field::utils::domain::make_attribute_marker<
-                mean_field::utils::domain::All, DomainSchema>(mesh);
+            return mean_field::utils::domain::make_attribute_marker<mean_field::utils::domain::All, DomainSchema>(mesh);
         case mean_field::utils::DOMAINS::STELLAR:
-            return mean_field::utils::domain::make_attribute_marker<
-                mean_field::utils::domain::Stellar, DomainSchema>(mesh);
+            return mean_field::utils::domain::make_attribute_marker<mean_field::utils::domain::Stellar, DomainSchema>(
+                mesh
+            );
         case mean_field::utils::DOMAINS::VACUUM:
-            return mean_field::utils::domain::make_attribute_marker<
-                mean_field::utils::domain::Vacuum, DomainSchema>(mesh);
+            return mean_field::utils::domain::make_attribute_marker<mean_field::utils::domain::Vacuum, DomainSchema>(
+                mesh
+            );
         }
         MFEM_ABORT("Unsupported integration domain.");
     }
@@ -62,15 +65,14 @@ namespace mean_field::analysis {
         mfem::LinearForm lf(fem.densityFes.get());
         mfem::GridFunctionCoefficient gf_c(&gf);
         double local_integral;
-        mfem::Array<int> elem_markers = make_domain_marker(*fem.mesh, domain);
+        mfem::Array<int> elem_markers                                    = make_domain_marker(*fem.mesh, domain);
         const mfem::ElementTransformation &representative_transformation = *fem.mesh->GetElementTransformation(0);
         const mfem::IntegrationRule &integration_rule =
             get_density_rule<field::Density::Form::MassConservation>(fem, representative_transformation, {}, domain);
 
         if (fem.has_mapping() && coord_space == mapping::COORDINATE_SPACE::PHYSICAL) {
             mapping::MappedScalarCoefficient mapped_gf_c(
-                *fem.domainMapperStateless, *fem.displacement,
-                *fem.compactificationCoordinate, gf_c
+                *fem.domainMapperStateless, *fem.displacement, *fem.compactificationCoordinate, gf_c
             );
 
             // ReSharper disable once CppDFAMemoryLeak // Disabled because MFEM
@@ -107,16 +109,14 @@ namespace mean_field::analysis {
     ) {
         const int dim = fem.mesh->Dimension();
         mapping::GridFunctionMappingEvaluator mapping_evaluator(
-            *fem.domainMapperStateless, *fem.displacement,
-            *fem.compactificationCoordinate
+            *fem.domainMapperStateless, *fem.displacement, *fem.compactificationCoordinate
         );
         mfem::Vector local_com(dim);
         local_com         = 0.0;
         double local_mass = 0.0;
 
         for (int i = 0; i < fem.mesh->GetNE(); ++i) {
-            if (!DomainSchema::template attribute_belongs_to<utils::domain::Stellar>(
-                    fem.mesh->GetAttribute(i)))
+            if (!DomainSchema::template attribute_belongs_to<utils::domain::Stellar>(fem.mesh->GetAttribute(i)))
                 continue;
             mfem::ElementTransformation *trans = fem.mesh->GetElementTransformation(i);
             const mfem::IntegrationRule &ir    = get_density_rule<field::Density::Form::CenterOfMass>(
@@ -129,16 +129,15 @@ namespace mean_field::analysis {
 
                 mapping::VolumeMappingContext mapping_context;
                 MFEM_VERIFY(
-                    mapping_evaluator.EvaluateVolume(*trans, ip, mapping_context) ==
-                        mapping::MappingStatus::valid,
+                    mapping_evaluator.EvaluateVolume(*trans, ip, mapping_context) == mapping::MappingStatus::valid,
                     "Center-of-mass integration encountered an invalid mapping."
                 );
-                const double weight = mapping_context.quadrature.weight;
-                double rho_val = rho.GetValue(i, ip);
+                const double weight            = mapping_context.quadrature.weight;
+                double rho_val                 = rho.GetValue(i, ip);
 
                 const mfem::Vector &phys_point = mapping_context.mapping.physical_position;
 
-                const double mass_term = rho_val * weight;
+                const double mass_term         = rho_val * weight;
                 local_mass += mass_term;
 
                 for (int d = 0; d < dim; ++d) {
@@ -183,8 +182,7 @@ namespace mean_field::analysis {
         std::unique_ptr<mfem::Coefficient> s2_coeff;
         if (fem.has_mapping()) {
             s2_coeff = std::make_unique<mapping::PhysicalPositionFunctionCoefficient>(
-                *fem.domainMapperStateless, *fem.displacement,
-                *fem.compactificationCoordinate, s2_func
+                *fem.domainMapperStateless, *fem.displacement, *fem.compactificationCoordinate, s2_func
             );
         } else {
             s2_coeff = std::make_unique<mfem::FunctionCoefficient>(s2_func);
@@ -204,8 +202,7 @@ namespace mean_field::analysis {
         double local_I = 0.0;
         if (fem.has_mapping()) {
             mapping::MappedScalarCoefficient mapped_integrand(
-                *fem.domainMapperStateless, *fem.displacement,
-                *fem.compactificationCoordinate, I_integrand
+                *fem.domainMapperStateless, *fem.displacement, *fem.compactificationCoordinate, I_integrand
             );
             auto *integrator = new mfem::DomainLFIntegrator(mapped_integrand);
             integrator->SetIntRule(&integration_rule);
@@ -239,18 +236,16 @@ namespace mean_field::analysis {
 
         double local_volume = 0.0;
         mapping::GridFunctionMappingEvaluator mapping_evaluator(
-            *fem.domainMapperStateless, *fem.displacement,
-            *fem.compactificationCoordinate
+            *fem.domainMapperStateless, *fem.displacement, *fem.compactificationCoordinate
         );
 
         for (int e = 0; e < mesh.GetNE(); ++e) {
-            const int attr = mesh.GetAttribute(e);
-            const bool selected =
-                domain == utils::DOMAINS::ALL ||
-                (domain == utils::DOMAINS::STELLAR &&
-                 DomainSchema::template attribute_belongs_to<utils::domain::Stellar>(attr)) ||
-                (domain == utils::DOMAINS::VACUUM &&
-                 DomainSchema::template attribute_belongs_to<utils::domain::Vacuum>(attr));
+            const int attr      = mesh.GetAttribute(e);
+            const bool selected = domain == utils::DOMAINS::ALL ||
+                                  (domain == utils::DOMAINS::STELLAR &&
+                                   DomainSchema::template attribute_belongs_to<utils::domain::Stellar>(attr)) ||
+                                  (domain == utils::DOMAINS::VACUUM &&
+                                   DomainSchema::template attribute_belongs_to<utils::domain::Vacuum>(attr));
             if (!selected)
                 continue;
             mfem::ElementTransformation *T = mesh.GetElementTransformation(e);
@@ -266,8 +261,7 @@ namespace mean_field::analysis {
                 if (physical) {
                     mapping::VolumeMappingContext context;
                     MFEM_VERIFY(
-                        mapping_evaluator.EvaluateVolume(*T, ip, context) ==
-                            mapping::MappingStatus::valid,
+                        mapping_evaluator.EvaluateVolume(*T, ip, context) == mapping::MappingStatus::valid,
                         "Mesh-volume integration encountered an invalid mapping."
                     );
                     dV = context.quadrature.weight;

libmeanfield/impl/fem.cpp

@@ -21,361 +21,322 @@ import :utils.misc;
 import :utils.user;
 
 namespace mean_field::fem {
-FEM setup_fem(const std::string &filename, const utils::Args &args,
-              const int extraRefine) {
-  FEM fem;
+    FEM setup_fem(
+        const std::string &filename,
+        const utils::Args &args,
+        const int extraRefine
+    ) {
+        FEM fem;
 
-  using GravityPotential = field::Gravity::Potential;
-  using GravityFlux = field::Gravity::Flux;
-  using DisplacementVector = field::Displacement::Vector;
-  using DensityScalar = field::Density::Scalar;
-  using EnthalpyScalar = field::Enthalpy::Scalar;
-  using DomainSchema = utils::domain::CoreEnvelopeVacuumDomainSchema;
+        using GravityPotential   = field::Gravity::Potential;
+        using GravityFlux        = field::Gravity::Flux;
+        using DisplacementVector = field::Displacement::Vector;
+        using DensityScalar      = field::Density::Scalar;
+        using EnthalpyScalar     = field::Enthalpy::Scalar;
+        using DomainSchema       = utils::domain::CoreEnvelopeVacuumDomainSchema;
 
-  // =====================================================================
-  // Section 1: Mesh construction
-  // =====================================================================
+        // =====================================================================
+        // Section 1: Mesh construction
+        // =====================================================================
 
-  fem.smesh = stroid::IO::LoadStroidMesh(filename).value();
+        fem.smesh                = stroid::IO::LoadStroidMesh(filename).value();
 
-  if (extraRefine > 0) {
-    stroid::refinement::UniformRefinement(fem.smesh, extraRefine);
-  }
+        if (extraRefine > 0) {
+            stroid::refinement::UniformRefinement(fem.smesh, extraRefine);
+        }
 
-  int mpiSize = 1;
-  MPI_Comm_size(MPI_COMM_WORLD, &mpiSize);
+        int mpiSize = 1;
+        MPI_Comm_size(MPI_COMM_WORLD, &mpiSize);
 
-  const std::unique_ptr<int[]> meshPartitioning(
-      fem.smesh.mesh->GeneratePartitioning(mpiSize, 1));
+        const std::unique_ptr<int[]> meshPartitioning(fem.smesh.mesh->GeneratePartitioning(mpiSize, 1));
 
-  fem.mesh = std::make_unique<mfem::ParMesh>(MPI_COMM_WORLD, *fem.smesh.mesh,
-                                             meshPartitioning.get(), 1);
+        fem.mesh = std::make_unique<mfem::ParMesh>(MPI_COMM_WORLD, *fem.smesh.mesh, meshPartitioning.get(), 1);
 
-  fem.mesh->EnsureNodes();
+        fem.mesh->EnsureNodes();
 
-  // =====================================================================
-  // Section 2: Exterior compactification coordinate
-  // =====================================================================
+        // =====================================================================
+        // Section 2: Exterior compactification coordinate
+        // =====================================================================
 
-  if (fem.smesh.exterior_coordinate == nullptr) {
-    throw std::runtime_error("Exterior coordinate not set.");
-  }
+        if (fem.smesh.exterior_coordinate == nullptr) {
+            throw std::runtime_error("Exterior coordinate not set.");
+        }
 
-  if (fem.smesh.exterior_coordinate->space == nullptr) {
-    throw std::runtime_error("Space for exterior coordinate not set.");
-  }
+        if (fem.smesh.exterior_coordinate->space == nullptr) {
+            throw std::runtime_error("Space for exterior coordinate not set.");
+        }
 
-  if (fem.smesh.exterior_coordinate->values == nullptr) {
-    throw std::runtime_error("Values for exterior coordinate not set.");
-  }
+        if (fem.smesh.exterior_coordinate->values == nullptr) {
+            throw std::runtime_error("Values for exterior coordinate not set.");
+        }
 
-  const mfem::FiniteElementSpace &serialCoordinateSpace =
-      *fem.smesh.exterior_coordinate->space;
+        const mfem::FiniteElementSpace &serialCoordinateSpace = *fem.smesh.exterior_coordinate->space;
 
-  const mfem::GridFunction &serialCoordinate =
-      *fem.smesh.exterior_coordinate->values;
+        const mfem::GridFunction &serialCoordinate            = *fem.smesh.exterior_coordinate->values;
 
-  if (serialCoordinate.FESpace() != &serialCoordinateSpace) {
-    throw std::runtime_error(
-        "Exterior coordinate values are not associated with the "
-        "supplied finite-element space.");
-  }
+        if (serialCoordinate.FESpace() != &serialCoordinateSpace) {
+            throw std::runtime_error(
+                "Exterior coordinate values are not associated with the "
+                "supplied finite-element space."
+            );
+        }
 
-  if (serialCoordinateSpace.GetMesh() != fem.smesh.mesh.get()) {
-    throw std::runtime_error(
-        "Exterior coordinate space is not associated with the "
-        "loaded STROID mesh.");
-  }
+        if (serialCoordinateSpace.GetMesh() != fem.smesh.mesh.get()) {
+            throw std::runtime_error(
+                "Exterior coordinate space is not associated with the "
+                "loaded STROID mesh."
+            );
+        }
 
-  if (serialCoordinateSpace.GetVDim() != 1) {
-    throw std::runtime_error("Exterior coordinate must be a scalar field.");
-  }
+        if (serialCoordinateSpace.GetVDim() != 1) {
+            throw std::runtime_error("Exterior coordinate must be a scalar field.");
+        }
 
-  if (serialCoordinate.Size() != serialCoordinateSpace.GetVSize()) {
-    throw std::runtime_error(
-        "Exterior coordinate value count does not match its "
-        "finite-element space.");
-  }
+        if (serialCoordinate.Size() != serialCoordinateSpace.GetVSize()) {
+            throw std::runtime_error(
+                "Exterior coordinate value count does not match its "
+                "finite-element space."
+            );
+        }
 
-  const int compactificationOrder = serialCoordinateSpace.GetMaxElementOrder();
+        const int compactificationOrder = serialCoordinateSpace.GetMaxElementOrder();
 
-  const int dimension = fem.mesh->Dimension();
+        const int dimension             = fem.mesh->Dimension();
 
-  fem.compactificationFec =
-      std::make_unique<mfem::H1_FECollection>(compactificationOrder, dimension);
+        fem.compactificationFec         = std::make_unique<mfem::H1_FECollection>(compactificationOrder, dimension);
 
-  fem.compactificationFes = std::make_unique<mfem::ParFiniteElementSpace>(
-      fem.mesh.get(), fem.compactificationFec.get());
+        fem.compactificationFes =
+            std::make_unique<mfem::ParFiniteElementSpace>(fem.mesh.get(), fem.compactificationFec.get());
 
-  mfem::ParGridFunction distributedCoordinate(fem.mesh.get(), &serialCoordinate,
-                                              meshPartitioning.get());
+        mfem::ParGridFunction distributedCoordinate(fem.mesh.get(), &serialCoordinate, meshPartitioning.get());
 
-  if (distributedCoordinate.Size() != fem.compactificationFes->GetVSize()) {
-    throw std::runtime_error(
-        "Distributed exterior coordinate does not match the "
-        "constructed parallel finite-element space.");
-  }
+        if (distributedCoordinate.Size() != fem.compactificationFes->GetVSize()) {
+            throw std::runtime_error(
+                "Distributed exterior coordinate does not match the "
+                "constructed parallel finite-element space."
+            );
+        }
 
-  fem.compactificationCoordinate =
-      std::make_unique<mfem::ParGridFunction>(fem.compactificationFes.get());
+        fem.compactificationCoordinate  = std::make_unique<mfem::ParGridFunction>(fem.compactificationFes.get());
 
-  *fem.compactificationCoordinate = distributedCoordinate;
+        *fem.compactificationCoordinate = distributedCoordinate;
 
-  double localMinimum = std::numeric_limits<double>::infinity();
+        double localMinimum             = std::numeric_limits<double>::infinity();
 
-  double localMaximum = -std::numeric_limits<double>::infinity();
+        double localMaximum             = -std::numeric_limits<double>::infinity();
 
-  for (int index = 0; index < fem.compactificationCoordinate->Size(); ++index) {
-    const double value = (*fem.compactificationCoordinate)(index);
+        for (int index = 0; index < fem.compactificationCoordinate->Size(); ++index) {
+            const double value = (*fem.compactificationCoordinate)(index);
 
-    if (!std::isfinite(value)) {
-      throw std::runtime_error(
-          "Exterior coordinate contains a non-finite value.");
+            if (!std::isfinite(value)) {
+                throw std::runtime_error("Exterior coordinate contains a non-finite value.");
+            }
+
+            localMinimum = std::min(localMinimum, value);
+
+            localMaximum = std::max(localMaximum, value);
+        }
+
+        double globalMinimum = 0.0;
+        double globalMaximum = 0.0;
+
+        MPI_Allreduce(&localMinimum, &globalMinimum, 1, MPI_DOUBLE, MPI_MIN, MPI_COMM_WORLD);
+
+        MPI_Allreduce(&localMaximum, &globalMaximum, 1, MPI_DOUBLE, MPI_MAX, MPI_COMM_WORLD);
+
+        constexpr double coordinateTolerance = 1.0e-12;
+
+        if (globalMinimum < -coordinateTolerance || globalMaximum > 1.0 + coordinateTolerance) {
+            throw std::runtime_error(
+                "Exterior coordinate lies outside the expected "
+                "interval [0, 1]."
+            );
+        }
+
+        // =====================================================================
+        // Section 3: Compile-time field realization
+        // =====================================================================
+
+        // ---------------------------------------------------------------------
+        // Gravity potential: scalar L2
+        // ---------------------------------------------------------------------
+
+        fem.gravityPotentialFec = GravityField::make_fec<GravityPotential>(dimension);
+
+        fem.gravityPotentialFes = GravityField::make_fespace<GravityPotential>(*fem.mesh, *fem.gravityPotentialFec);
+
+        // ---------------------------------------------------------------------
+        // Gravity flux: H(div)/RT. Basis choices are encoded by field.mfem.
+        // ---------------------------------------------------------------------
+
+        fem.gravityFluxFec      = GravityField::make_fec<GravityFlux>(dimension);
+
+        fem.gravityFluxFes      = GravityField::make_fespace<GravityFlux>(*fem.mesh, *fem.gravityFluxFec);
+
+        // ---------------------------------------------------------------------
+        // Displacement: vector H1. Ordering is encoded by field.mfem.
+        // ---------------------------------------------------------------------
+
+        fem.displacementFec     = DisplacementField::make_fec<DisplacementVector>(dimension);
+
+        fem.displacementFes     = DisplacementField::make_fespace<DisplacementVector>(*fem.mesh, *fem.displacementFec);
+
+        fem.displacement        = std::make_unique<mfem::ParGridFunction>(fem.displacementFes.get());
+
+        *fem.displacement       = 0.0;
+
+        // ---------------------------------------------------------------------
+        // Density: scalar discontinuous L2
+        // ---------------------------------------------------------------------
+
+        fem.densityFec          = DensityField::make_fec<DensityScalar>(dimension);
+
+        fem.densityFes          = DensityField::make_fespace<DensityScalar>(*fem.mesh, *fem.densityFec);
+
+        // ---------------------------------------------------------------------
+        // Specific enthalpy: scalar continuous H1
+        // ---------------------------------------------------------------------
+
+        fem.enthalpyFec         = EnthalpyField::make_fec<EnthalpyScalar>(dimension);
+
+        fem.enthalpyFes         = EnthalpyField::make_fespace<EnthalpyScalar>(*fem.mesh, *fem.enthalpyFec);
+
+        // =====================================================================
+        // Section 4: Multipole data
+        // =====================================================================
+
+        fem.com.SetSize(dimension);
+        fem.com = 0.0;
+
+        fem.Q.SetSize(dimension, dimension);
+        fem.Q                            = 0.0;
+
+        // =====================================================================
+        // Section 5: Boundary markers
+        // =====================================================================
+
+        const int boundaryAttributeCount = fem.mesh->bdr_attributes.Max();
+
+        fem.boundaryContext.inf_bounds.SetSize(boundaryAttributeCount);
+
+        fem.boundaryContext.stellar_bounds.SetSize(boundaryAttributeCount);
+
+        fem.boundaryContext.inf_bounds                                                                  = 0;
+        fem.boundaryContext.stellar_bounds                                                              = 0;
+
+        fem.boundaryContext.inf_bounds[static_cast<int>(boundary::Boundaries::INF_SURFACE) - 1]         = 1;
+
+        fem.boundaryContext.stellar_bounds[static_cast<int>(boundary::Boundaries::STELLAR_SURFACE) - 1] = 1;
+
+        // =====================================================================
+        // Section 7: Quadrature policy
+        // =====================================================================
+
+        const quadrature::QuadratureOptions &quadratureOptions = args.quadrature;
+
+        if (quadratureOptions.validation.reject_negative_boosts && quadratureOptions.global_boost < 0) {
+            throw std::invalid_argument("Global quadrature boost cannot be negative.");
+        }
+
+        quadrature::RuleSet quadratureRuleSet =
+            quadrature::make_rule_set(quadratureOptions.mode, quadratureOptions.global_boost);
+
+        if (quadratureOptions.fallback_fixed_order.has_value()) {
+            if (*quadratureOptions.fallback_fixed_order < 0) {
+                throw std::invalid_argument("Fallback quadrature order cannot be negative.");
+            }
+
+            quadratureRuleSet.fallback.fixed_order = quadratureOptions.fallback_fixed_order;
+        }
+
+        auto apply_quadrature_options = [&quadratureOptions](
+                                            quadrature::RuleControl &ruleControl,
+                                            const quadrature::QuadratureTermOptions &termOptions
+                                        ) {
+            if (termOptions.fixed_order.has_value() && *termOptions.fixed_order < 0) {
+                throw std::invalid_argument("Fixed quadrature order cannot be negative.");
+            }
+
+            if (quadratureOptions.validation.reject_negative_boosts && termOptions.additional_boost < 0) {
+                throw std::invalid_argument("Term quadrature boost cannot be negative.");
+            }
+
+            ruleControl.boost += termOptions.additional_boost;
+
+            if (termOptions.fixed_order.has_value()) {
+                ruleControl.fixed_order = termOptions.fixed_order;
+            }
+        };
+
+        apply_quadrature_options(quadratureRuleSet.gravity_hdiv_mass, quadratureOptions.gravity_hdiv_mass);
+
+        apply_quadrature_options(quadratureRuleSet.gravity_divergence, quadratureOptions.gravity_divergence);
+
+        apply_quadrature_options(quadratureRuleSet.gravity_source, quadratureOptions.gravity_source);
+
+        apply_quadrature_options(quadratureRuleSet.gravity_force, quadratureOptions.gravity_force);
+
+        apply_quadrature_options(quadratureRuleSet.gravity_boundary, quadratureOptions.gravity_boundary);
+
+        apply_quadrature_options(quadratureRuleSet.centrifugal, quadratureOptions.centrifugal);
+
+        apply_quadrature_options(quadratureRuleSet.density_projection, quadratureOptions.density_projection);
+
+        apply_quadrature_options(quadratureRuleSet.eos_closure, quadratureOptions.eos_closure);
+
+        apply_quadrature_options(quadratureRuleSet.hydrostatic_equilibrium, quadratureOptions.hydrostatic_equilibrium);
+
+        apply_quadrature_options(quadratureRuleSet.isobaric_surface, quadratureOptions.isobaric_surface);
+
+        apply_quadrature_options(quadratureRuleSet.mesh_extension, quadratureOptions.mesh_extension);
+
+        apply_quadrature_options(quadratureRuleSet.mass_conservation, quadratureOptions.mass_conservation);
+
+        apply_quadrature_options(quadratureRuleSet.mass_normalization, quadratureOptions.mass_normalization);
+
+        apply_quadrature_options(quadratureRuleSet.center_of_mass, quadratureOptions.center_of_mass);
+
+        apply_quadrature_options(quadratureRuleSet.quadrupole, quadratureOptions.quadrupole);
+
+        apply_quadrature_options(quadratureRuleSet.gravitational_energy, quadratureOptions.gravitational_energy);
+
+        apply_quadrature_options(quadratureRuleSet.pressure_integral, quadratureOptions.pressure_integral);
+
+        apply_quadrature_options(quadratureRuleSet.pressure_force, quadratureOptions.pressure_force);
+
+        apply_quadrature_options(quadratureRuleSet.virial, quadratureOptions.virial);
+
+        apply_quadrature_options(quadratureRuleSet.error_norm, quadratureOptions.error_norm);
+
+        apply_quadrature_options(quadratureRuleSet.roles.discretization, quadratureOptions.roles.discretization);
+
+        apply_quadrature_options(quadratureRuleSet.roles.preconditioner, quadratureOptions.roles.preconditioner);
+
+        apply_quadrature_options(quadratureRuleSet.roles.diagnostic, quadratureOptions.roles.diagnostic);
+
+        apply_quadrature_options(quadratureRuleSet.roles.projection, quadratureOptions.roles.projection);
+
+        fem.quadratureFactory =
+            std::make_unique<quadrature::RuleFactory>(quadrature::Policy(std::move(quadratureRuleSet)));
+
+        // =====================================================================
+        // Section 11: Stateless domain mapper
+        // =====================================================================
+
+        auto exteriorDomain =
+            std::make_unique<const mapping::compactification::KelvinCompactification>(args.kelvin_options);
+
+        MFEM_VERIFY(
+            args.domain_mapper_options.vacuum_element_attribute ==
+                DomainSchema::template material_attribute<utils::domain::Vacuum>(),
+            "The domain-mapper compactification attribute must match the vacuum "
+            "material registered by the "
+            "production domain schema."
+        );
+
+        fem.domainMapperStateless =
+            std::make_unique<mapping::DomainMapper>(args.domain_mapper_options, std::move(exteriorDomain));
+
+        return fem;
     }
-
-    localMinimum = std::min(localMinimum, value);
-
-    localMaximum = std::max(localMaximum, value);
-  }
-
-  double globalMinimum = 0.0;
-  double globalMaximum = 0.0;
-
-  MPI_Allreduce(&localMinimum, &globalMinimum, 1, MPI_DOUBLE, MPI_MIN,
-                MPI_COMM_WORLD);
-
-  MPI_Allreduce(&localMaximum, &globalMaximum, 1, MPI_DOUBLE, MPI_MAX,
-                MPI_COMM_WORLD);
-
-  constexpr double coordinateTolerance = 1.0e-12;
-
-  if (globalMinimum < -coordinateTolerance ||
-      globalMaximum > 1.0 + coordinateTolerance) {
-    throw std::runtime_error("Exterior coordinate lies outside the expected "
-                             "interval [0, 1].");
-  }
-
-  // =====================================================================
-  // Section 3: Compile-time field realization
-  // =====================================================================
-
-  // ---------------------------------------------------------------------
-  // Gravity potential: scalar L2
-  // ---------------------------------------------------------------------
-
-  fem.gravityPotentialFec = GravityField::make_fec<GravityPotential>(dimension);
-
-  fem.gravityPotentialFes = GravityField::make_fespace<GravityPotential>(
-      *fem.mesh, *fem.gravityPotentialFec);
-
-  // ---------------------------------------------------------------------
-  // Gravity flux: H(div)/RT. Basis choices are encoded by field.mfem.
-  // ---------------------------------------------------------------------
-
-  fem.gravityFluxFec = GravityField::make_fec<GravityFlux>(dimension);
-
-  fem.gravityFluxFes =
-      GravityField::make_fespace<GravityFlux>(*fem.mesh, *fem.gravityFluxFec);
-
-  // ---------------------------------------------------------------------
-  // Displacement: vector H1. Ordering is encoded by field.mfem.
-  // ---------------------------------------------------------------------
-
-  fem.displacementFec =
-      DisplacementField::make_fec<DisplacementVector>(dimension);
-
-  fem.displacementFes = DisplacementField::make_fespace<DisplacementVector>(
-      *fem.mesh, *fem.displacementFec);
-
-  fem.displacement =
-      std::make_unique<mfem::ParGridFunction>(fem.displacementFes.get());
-
-  *fem.displacement = 0.0;
-
-  // ---------------------------------------------------------------------
-  // Density: scalar discontinuous L2
-  // ---------------------------------------------------------------------
-
-  fem.densityFec = DensityField::make_fec<DensityScalar>(dimension);
-
-  fem.densityFes =
-      DensityField::make_fespace<DensityScalar>(*fem.mesh, *fem.densityFec);
-
-  // ---------------------------------------------------------------------
-  // Specific enthalpy: scalar continuous H1
-  // ---------------------------------------------------------------------
-
-  fem.enthalpyFec = EnthalpyField::make_fec<EnthalpyScalar>(dimension);
-
-  fem.enthalpyFes =
-      EnthalpyField::make_fespace<EnthalpyScalar>(*fem.mesh, *fem.enthalpyFec);
-
-  // =====================================================================
-  // Section 4: Multipole data
-  // =====================================================================
-
-  fem.com.SetSize(dimension);
-  fem.com = 0.0;
-
-  fem.Q.SetSize(dimension, dimension);
-  fem.Q = 0.0;
-
-  // =====================================================================
-  // Section 5: Boundary markers
-  // =====================================================================
-
-  const int boundaryAttributeCount = fem.mesh->bdr_attributes.Max();
-
-  fem.boundaryContext.inf_bounds.SetSize(boundaryAttributeCount);
-
-  fem.boundaryContext.stellar_bounds.SetSize(boundaryAttributeCount);
-
-  fem.boundaryContext.inf_bounds = 0;
-  fem.boundaryContext.stellar_bounds = 0;
-
-  fem.boundaryContext
-      .inf_bounds[static_cast<int>(boundary::Boundaries::INF_SURFACE) - 1] = 1;
-
-  fem.boundaryContext
-      .stellar_bounds[static_cast<int>(boundary::Boundaries::STELLAR_SURFACE) -
-                      1] = 1;
-
-  // =====================================================================
-  // Section 7: Quadrature policy
-  // =====================================================================
-
-  const quadrature::QuadratureOptions &quadratureOptions = args.quadrature;
-
-  if (quadratureOptions.validation.reject_negative_boosts &&
-      quadratureOptions.global_boost < 0) {
-    throw std::invalid_argument("Global quadrature boost cannot be negative.");
-  }
-
-  quadrature::RuleSet quadratureRuleSet = quadrature::make_rule_set(
-      quadratureOptions.mode, quadratureOptions.global_boost);
-
-  if (quadratureOptions.fallback_fixed_order.has_value()) {
-    if (*quadratureOptions.fallback_fixed_order < 0) {
-      throw std::invalid_argument(
-          "Fallback quadrature order cannot be negative.");
-    }
-
-    quadratureRuleSet.fallback.fixed_order =
-        quadratureOptions.fallback_fixed_order;
-  }
-
-  auto apply_quadrature_options = [&quadratureOptions](
-                                      quadrature::RuleControl &ruleControl,
-                                      const quadrature::QuadratureTermOptions
-                                          &termOptions) {
-    if (termOptions.fixed_order.has_value() && *termOptions.fixed_order < 0) {
-      throw std::invalid_argument("Fixed quadrature order cannot be negative.");
-    }
-
-    if (quadratureOptions.validation.reject_negative_boosts &&
-        termOptions.additional_boost < 0) {
-      throw std::invalid_argument("Term quadrature boost cannot be negative.");
-    }
-
-    ruleControl.boost += termOptions.additional_boost;
-
-    if (termOptions.fixed_order.has_value()) {
-      ruleControl.fixed_order = termOptions.fixed_order;
-    }
-  };
-
-  apply_quadrature_options(quadratureRuleSet.gravity_hdiv_mass,
-                           quadratureOptions.gravity_hdiv_mass);
-
-  apply_quadrature_options(quadratureRuleSet.gravity_divergence,
-                           quadratureOptions.gravity_divergence);
-
-  apply_quadrature_options(quadratureRuleSet.gravity_source,
-                           quadratureOptions.gravity_source);
-
-  apply_quadrature_options(quadratureRuleSet.gravity_force,
-                           quadratureOptions.gravity_force);
-
-  apply_quadrature_options(quadratureRuleSet.gravity_boundary,
-                           quadratureOptions.gravity_boundary);
-
-  apply_quadrature_options(quadratureRuleSet.centrifugal,
-                           quadratureOptions.centrifugal);
-
-  apply_quadrature_options(quadratureRuleSet.density_projection,
-                           quadratureOptions.density_projection);
-
-  apply_quadrature_options(quadratureRuleSet.eos_closure,
-                           quadratureOptions.eos_closure);
-
-  apply_quadrature_options(quadratureRuleSet.hydrostatic_equilibrium,
-                           quadratureOptions.hydrostatic_equilibrium);
-
-  apply_quadrature_options(quadratureRuleSet.isobaric_surface,
-                           quadratureOptions.isobaric_surface);
-
-  apply_quadrature_options(quadratureRuleSet.mesh_extension,
-                           quadratureOptions.mesh_extension);
-
-  apply_quadrature_options(quadratureRuleSet.mass_conservation,
-                           quadratureOptions.mass_conservation);
-
-  apply_quadrature_options(quadratureRuleSet.mass_normalization,
-                           quadratureOptions.mass_normalization);
-
-  apply_quadrature_options(quadratureRuleSet.center_of_mass,
-                           quadratureOptions.center_of_mass);
-
-  apply_quadrature_options(quadratureRuleSet.quadrupole,
-                           quadratureOptions.quadrupole);
-
-  apply_quadrature_options(quadratureRuleSet.gravitational_energy,
-                           quadratureOptions.gravitational_energy);
-
-  apply_quadrature_options(quadratureRuleSet.pressure_integral,
-                           quadratureOptions.pressure_integral);
-
-  apply_quadrature_options(quadratureRuleSet.pressure_force,
-                           quadratureOptions.pressure_force);
-
-  apply_quadrature_options(quadratureRuleSet.virial, quadratureOptions.virial);
-
-  apply_quadrature_options(quadratureRuleSet.error_norm,
-                           quadratureOptions.error_norm);
-
-  apply_quadrature_options(quadratureRuleSet.roles.discretization,
-                           quadratureOptions.roles.discretization);
-
-  apply_quadrature_options(quadratureRuleSet.roles.preconditioner,
-                           quadratureOptions.roles.preconditioner);
-
-  apply_quadrature_options(quadratureRuleSet.roles.diagnostic,
-                           quadratureOptions.roles.diagnostic);
-
-  apply_quadrature_options(quadratureRuleSet.roles.projection,
-                           quadratureOptions.roles.projection);
-
-  fem.quadratureFactory = std::make_unique<quadrature::RuleFactory>(
-      quadrature::Policy(std::move(quadratureRuleSet)));
-
-  // =====================================================================
-  // Section 11: Stateless domain mapper
-  // =====================================================================
-
-  auto exteriorDomain =
-      std::make_unique<const mapping::compactification::KelvinCompactification>(
-          args.kelvin_options);
-
-  MFEM_VERIFY(
-      args.domain_mapper_options.vacuum_element_attribute ==
-          DomainSchema::template material_attribute<utils::domain::Vacuum>(),
-      "The domain-mapper compactification attribute must match the vacuum "
-      "material registered by the "
-      "production domain schema.");
-
-  fem.domainMapperStateless = std::make_unique<mapping::DomainMapper>(
-      args.domain_mapper_options, std::move(exteriorDomain));
-
-  return fem;
-}
 } // namespace mean_field::fem

libmeanfield/impl/integrators/advection.cpp

@@ -9,7 +9,11 @@ namespace mean_field::integrators {
         const mfem::GridFunction &displacement,
         const mfem::GridFunction &compactification_coordinate
     )
-        : m_mapping(mapper, displacement, compactification_coordinate) {
+        : m_mapping(
+              mapper,
+              displacement,
+              compactification_coordinate
+          ) {
     }
 
     void AdvectionIntegrator::AssembleElementVector(

libmeanfield/impl/integrators/centrifugal.cpp

@@ -9,7 +9,11 @@ namespace mean_field::integrators {
         const mfem::GridFunction &compactification_coordinate,
         const mfem::Vector &omega
     )
-        : m_mapping(mapper, displacement, compactification_coordinate),
+        : m_mapping(
+              mapper,
+              displacement,
+              compactification_coordinate
+          ),
           m_omega(3) {
         MFEM_ASSERT(omega.Size() == 3, "Omega vector must be 3D");
         m_omega = omega;

libmeanfield/impl/integrators/coriolis.cpp

@@ -10,7 +10,11 @@ namespace mean_field::integrators {
         const mfem::GridFunction &compactification_coordinate,
         const mfem::Vector &omega
     )
-        : m_mapping(mapper, displacement, compactification_coordinate),
+        : m_mapping(
+              mapper,
+              displacement,
+              compactification_coordinate
+          ),
           m_omega(omega) {
         m_omega_mat.SetSize(3, 3);
         m_omega_mat       = 0.0;

libmeanfield/impl/integrators/gravity.cpp

@@ -19,7 +19,11 @@ namespace mean_field::integrators {
         const mfem::GridFunction &compactification_coordinate,
         const GravityForceJacobianMode jacobian_mode
     )
-        : m_mapping(mapper, displacement, compactification_coordinate),
+        : m_mapping(
+              mapper,
+              displacement,
+              compactification_coordinate
+          ),
           m_jacobian_mode(jacobian_mode) {
     }
 

libmeanfield/impl/integrators/mass_continuity.cpp

@@ -9,7 +9,11 @@ namespace mean_field::integrators {
         const mfem::GridFunction &displacement,
         const mfem::GridFunction &compactification_coordinate
     )
-        : m_mapping(mapper, displacement, compactification_coordinate) { };
+        : m_mapping(
+              mapper,
+              displacement,
+              compactification_coordinate
+          ) { };
 
     void ContinuityVolumeIntegrator::AssembleElementVector(
         const mfem::Array<const mfem::FiniteElement *> &el,
@@ -174,7 +178,11 @@ namespace mean_field::integrators {
         const mfem::GridFunction &displacement,
         const mfem::GridFunction &compactification_coordinate
     )
-        : m_mapping(mapper, displacement, compactification_coordinate) {
+        : m_mapping(
+              mapper,
+              displacement,
+              compactification_coordinate
+          ) {
     }
 
     void ContinuityFaceIntegrator::AssembleFaceVector(
@@ -206,11 +214,11 @@ namespace mean_field::integrators {
         }
         mfem::Vector &r_rho = *elvect[1];
         r_rho.SetSize(dof_rho_minus + dof_rho_plus);
-        r_rho                     = 0.0;
+        r_rho                = 0.0;
 
-        const int attr_minus      = Tr.Elem1->Attribute;
-        const int attr_plus       = (Tr.Elem2 != nullptr) ? Tr.Elem2->Attribute : -1;
-        using DomainSchema = utils::domain::CoreEnvelopeVacuumDomainSchema;
+        const int attr_minus = Tr.Elem1->Attribute;
+        const int attr_plus  = (Tr.Elem2 != nullptr) ? Tr.Elem2->Attribute : -1;
+        using DomainSchema   = utils::domain::CoreEnvelopeVacuumDomainSchema;
         if (DomainSchema::template attribute_belongs_to<utils::domain::Vacuum>(attr_minus) ||
             DomainSchema::template attribute_belongs_to<utils::domain::Vacuum>(attr_plus)) {
             return; // No flux contribution for vacuum faces
@@ -416,9 +424,9 @@ namespace mean_field::integrators {
     }
 
     bool ContinuityFaceIntegrator::skip_face(const mfem::FaceElementTransformations &Tr) {
-        const int attr_minus      = Tr.Elem1->Attribute;
-        const int attr_plus       = (Tr.Elem2 != nullptr) ? Tr.Elem2->Attribute : -1;
-        using DomainSchema = utils::domain::CoreEnvelopeVacuumDomainSchema;
+        const int attr_minus = Tr.Elem1->Attribute;
+        const int attr_plus  = (Tr.Elem2 != nullptr) ? Tr.Elem2->Attribute : -1;
+        using DomainSchema   = utils::domain::CoreEnvelopeVacuumDomainSchema;
         if (DomainSchema::template attribute_belongs_to<utils::domain::Vacuum>(attr_minus) ||
             DomainSchema::template attribute_belongs_to<utils::domain::Vacuum>(attr_plus)) {
             return true; // No flux contribution for vacuum faces

libmeanfield/impl/integrators/viscosity.cpp

@@ -10,7 +10,11 @@ namespace mean_field::integrators {
         const double mu,
         const int quad_boost
     )
-        : m_mapping(mapper, displacement, compactification_coordinate),
+        : m_mapping(
+              mapper,
+              displacement,
+              compactification_coordinate
+          ),
           m_mu(mu),
           m_quad_boost(quad_boost) {
     }

libmeanfield/impl/mapping/coefficients.cpp

@@ -15,7 +15,11 @@ namespace mean_field::mapping {
         Coefficient &coeff,
         const COORDINATE_SPACE coord_space
     )
-        : m_mapping(mapper, displacement, compactification_coordinate),
+        : m_mapping(
+              mapper,
+              displacement,
+              compactification_coordinate
+          ),
           m_coeff(coeff),
           m_coord_space(coord_space) { };
 
@@ -28,7 +32,7 @@ namespace mean_field::mapping {
 
         switch (m_coord_space) {
         case COORDINATE_SPACE::PHYSICAL: {
-            f_val             = eval_at_point(m_coeff, T, ip);
+            f_val = eval_at_point(m_coeff, T, ip);
             VolumeMappingContext context;
             MFEM_VERIFY(
                 m_mapping.EvaluateVolume(T, ip, context) == MappingStatus::valid,
@@ -63,7 +67,11 @@ namespace mean_field::mapping {
         const int dim
     )
         : MatrixCoefficient(dim),
-          m_mapping(mapper, displacement, compactification_coordinate),
+          m_mapping(
+              mapper,
+              displacement,
+              compactification_coordinate
+          ),
           m_scalar(&sigma),
           m_tensor(nullptr) { };
 
@@ -74,7 +82,11 @@ namespace mean_field::mapping {
         MatrixCoefficient &sigma
     )
         : MatrixCoefficient(sigma.GetHeight()),
-          m_mapping(mapper, displacement, compactification_coordinate),
+          m_mapping(
+              mapper,
+              displacement,
+              compactification_coordinate
+          ),
           m_scalar(nullptr),
           m_tensor(&sigma) { };
 
@@ -92,7 +104,7 @@ namespace mean_field::mapping {
             "Mapped diffusion coefficient encountered an invalid mapping."
         );
         const mfem::DenseMatrix &JInv = context.mapping.inverse_mapping_jacobian;
-        const double detJ = context.mapping.mapping_determinant;
+        const double detJ             = context.mapping.mapping_determinant;
 
         if (m_scalar) {
             const double sig_val = m_scalar->Eval(T, ip);
@@ -120,7 +132,11 @@ namespace mean_field::mapping {
         VectorCoefficient &coeff
     )
         : VectorCoefficient(coeff.GetVDim()),
-          m_mapping(mapper, displacement, compactification_coordinate),
+          m_mapping(
+              mapper,
+              displacement,
+              compactification_coordinate
+          ),
           m_coeff(coeff) { };
 
     void MappedVectorCoefficient::Eval(
@@ -137,7 +153,7 @@ namespace mean_field::mapping {
             "Mapped vector coefficient encountered an invalid mapping."
         );
         const mfem::DenseMatrix &JInv = context.mapping.inverse_mapping_jacobian;
-        const double detJ = context.mapping.mapping_determinant;
+        const double detJ             = context.mapping.mapping_determinant;
 
         mfem::Vector C_phys(dim);
         m_coeff.Eval(C_phys, T, ip);
@@ -157,7 +173,11 @@ namespace mean_field::mapping {
         Func f // std::function<double(const mfem::Vector&)>
     )
         : m_f(std::move(f)),
-          m_mapping(mapper, displacement, compactification_coordinate) { };
+          m_mapping(
+              mapper,
+              displacement,
+              compactification_coordinate
+          ) { };
 
     double PhysicalPositionFunctionCoefficient::Eval(
         mfem::ElementTransformation &T,
@@ -179,7 +199,11 @@ namespace mean_field::mapping {
         const int dim
     )
         : MatrixCoefficient(dim),
-          m_mapping(mapper, displacement, compactification_coordinate) {
+          m_mapping(
+              mapper,
+              displacement,
+              compactification_coordinate
+          ) {
     }
 
     void MappedHDivMassCoefficient::Eval(
@@ -195,7 +219,7 @@ namespace mean_field::mapping {
             "Mapped H(div) coefficient encountered an invalid mapping."
         );
         const mfem::DenseMatrix &map_jacobian = context.mapping.mapping_jacobian;
-        const double map_determinant = context.mapping.mapping_determinant;
+        const double map_determinant          = context.mapping.mapping_determinant;
 
         MFEM_VERIFY(map_determinant > 0.0, "Domain mapping has a non-positive Jacobian determinant.");
 

libmeanfield/impl/models/polytropic.cpp

@@ -15,7 +15,7 @@ namespace mean_field::models::structure {
         validate();
     }
 
-    const eos::EquationOfState &PolytropicStructure::equationOfState() const noexcept {
+    const eos::Polytrope &PolytropicStructure::equationOfState() const noexcept {
         return m_equationOfState;
     }
 
@@ -29,7 +29,9 @@ namespace mean_field::models::structure {
         const double polytropicIndex                        = m_equationOfState.polytropic_index();
         const std::vector<LaneEmdenPoint> laneEmdenSolution = solveLaneEmden(polytropicIndex);
         const double surfaceCoordinate                      = laneEmdenSolution.back().coordinate;
-        const double centralEnthalpy = m_equationOfState.enthalpy_from_density(request.centralDensity);
+        const double centralEnthalpy =
+            eos::evaluate<eos::quantity::SpecificEnthalpy>(m_equationOfState, eos::DensityValue{request.centralDensity})
+                .value();
         const double radialScaleSquared =
             centralEnthalpy / (4.0 * std::numbers::pi_v<double> * mean_field::utils::G * request.centralDensity);
 
@@ -61,11 +63,12 @@ namespace mean_field::models::structure {
             const double dimensionlessRadius = sampleFraction * surfaceCoordinate;
             const double laneEmdenValue =
                 interpolateLaneEmdenValue(laneEmdenSolution, dimensionlessRadius, interpolationIndex);
-            const double density       = request.centralDensity * std::pow(laneEmdenValue, polytropicIndex);
+            const double density      = request.centralDensity * std::pow(laneEmdenValue, polytropicIndex);
 
-            seed.radius(sampleIndex)   = radialScale * dimensionlessRadius;
-            seed.density(sampleIndex)  = density;
-            seed.enthalpy(sampleIndex) = m_equationOfState.enthalpy_from_density(density);
+            seed.radius(sampleIndex)  = radialScale * dimensionlessRadius;
+            seed.density(sampleIndex) = density;
+            seed.enthalpy(sampleIndex) =
+                eos::evaluate<eos::quantity::SpecificEnthalpy>(m_equationOfState, eos::DensityValue{density}).value();
         }
 
         seed.radius(0)              = 0.0;

libmeanfield/impl/operators/contexts/hydrostatic_equilibrium_context.cpp

@@ -80,13 +80,19 @@ namespace mean_field::operators::context::hydrostatic {
         : m_f(f),
           m_domainMapper(domainMapper),
           m_enthalpyMap(
-              field::make_field_dof_map<field::Enthalpy, DomainSchema>(*f.enthalpyFes)
+              field::make_field_dof_map<
+                  field::Enthalpy,
+                  DomainSchema>(*f.enthalpyFes)
           ),
           m_gravityPotentialMap(
-              field::make_field_dof_map<field::Gravity, DomainSchema>(*f.gravityPotentialFes)
+              field::make_field_dof_map<
+                  field::Gravity,
+                  DomainSchema>(*f.gravityPotentialFes)
           ),
           m_displacementMap(
-              field::make_field_dof_map<field::Displacement, DomainSchema>(*f.displacementFes)
+              field::make_field_dof_map<
+                  field::Displacement,
+                  DomainSchema>(*f.displacementFes)
           ) {
         MFEM_VERIFY(m_f.mesh != nullptr, "HydrostaticEquilibriumContext requires a mesh.");
 

libmeanfield/impl/operators/kernels/barotropic_closure_kernels.cpp

@@ -12,6 +12,8 @@ import :field.registry;
 import :utils.domain;
 
 namespace {
+    namespace eos       = mean_field::eos;
+
     using DomainSchema  = mean_field::utils::domain::CoreEnvelopeVacuumDomainSchema;
     using ClosureDomain = mean_field::field::FieldDomainT<mean_field::field::Density>;
 
@@ -336,11 +338,21 @@ namespace {
                     if (closureAction == ClosureAction::residual) {
                         const double density = elementDensityInput * densityShape;
 
-                        integrand            = density - barotrope.density_from_enthalpy(baseEnthalpy);
+                        const double equationOfStateDensity =
+                            eos::evaluate<eos::quantity::Density>(barotrope, eos::SpecificEnthalpyValue{baseEnthalpy})
+                                .value();
+
+                        integrand = density - equationOfStateDensity;
                     } else {
                         const double enthalpyVariation = elementEnthalpyVariation * enthalpyShape;
 
-                        integrand = -barotrope.density_derivative_from_enthalpy(baseEnthalpy) * enthalpyVariation;
+                        const double densityDerivative =
+                            eos::partialDerivative<eos::quantity::Density, eos::quantity::SpecificEnthalpy>(
+                                barotrope, eos::SpecificEnthalpyValue{baseEnthalpy}
+                            )
+                                .value();
+
+                        integrand = -densityDerivative * enthalpyVariation;
                     }
                 }
 
@@ -628,11 +640,14 @@ namespace mean_field::operators::kernels {
 
                 enthalpyElement.CalcShape(integrationPoint, enthalpyShape);
 
-                const double densityValue        = elementBaseDensity * densityShape;
+                const double densityValue  = elementBaseDensity * densityShape;
 
-                const double enthalpyValue       = elementBaseEnthalpy * enthalpyShape;
+                const double enthalpyValue = elementBaseEnthalpy * enthalpyShape;
 
-                const double closureValue        = densityValue - barotrope.density_from_enthalpy(enthalpyValue);
+                const double equationOfStateDensity =
+                    eos::evaluate<eos::quantity::Density>(barotrope, eos::SpecificEnthalpyValue{enthalpyValue}).value();
+
+                const double closureValue        = densityValue - equationOfStateDensity;
 
                 const double geometryActionValue = closureValue * mappingVariation.weight_variation;
 

libmeanfield/impl/operators/prepared_barotropic_closure.cpp

@@ -398,11 +398,17 @@ namespace mean_field::operators {
                     data.enthalpyBasis(quadraturePoint, enthalpyDof) = enthalpyShape(enthalpyDof);
                 }
 
-                const double density            = elementBaseDensity * densityShape;
-                const double enthalpy           = elementBaseEnthalpy * enthalpyShape;
-                const double quadratureWeight   = mappingContext.quadrature.weight;
-                const double eosDensity         = m_equationOfState.density_from_enthalpy(enthalpy);
-                const double enthalpyDerivative = m_equationOfState.density_derivative_from_enthalpy(enthalpy);
+                const double density          = elementBaseDensity * densityShape;
+                const double enthalpy         = elementBaseEnthalpy * enthalpyShape;
+                const double quadratureWeight = mappingContext.quadrature.weight;
+                const eos::SpecificEnthalpyValue specificEnthalpy{enthalpy};
+                const double eosDensity =
+                    eos::evaluate<eos::quantity::Density>(m_equationOfState, specificEnthalpy).value();
+                const double enthalpyDerivative =
+                    eos::partialDerivative<eos::quantity::Density, eos::quantity::SpecificEnthalpy>(
+                        m_equationOfState, specificEnthalpy
+                    )
+                        .value();
 
                 MFEM_VERIFY(
                     std::isfinite(quadratureWeight) && quadratureWeight > 0.0 && std::isfinite(eosDensity) &&

libmeanfield/impl/operators/prepared_gravity_source.cpp

@@ -9,531 +9,535 @@ module mean_field;
 import :operators.prepared_gravity_source;
 
 namespace {
-using DomainSchema = mean_field::utils::domain::CoreEnvelopeVacuumDomainSchema;
+    using DomainSchema = mean_field::utils::domain::CoreEnvelopeVacuumDomainSchema;
 
-int get_operator_height(const mean_field::fem::FEM &f) {
-  MFEM_VERIFY(f.gravityPotentialFes != nullptr,
-              "PreparedMappedGravitySourceOperator requires the "
-              "gravity-potential "
-              "finite-element space.");
-  return mean_field::field::make_field_dof_map<mean_field::field::Gravity,
-                                               DomainSchema>(
-             *f.gravityPotentialFes)
-      .reduced_size();
-}
+    int get_operator_height(const mean_field::fem::FEM &f) {
+        MFEM_VERIFY(
+            f.gravityPotentialFes != nullptr, "PreparedMappedGravitySourceOperator requires the "
+                                              "gravity-potential "
+                                              "finite-element space."
+        );
+        return mean_field::field::make_field_dof_map<mean_field::field::Gravity, DomainSchema>(*f.gravityPotentialFes)
+            .reduced_size();
+    }
 
-int get_operator_width(const mean_field::fem::FEM &f) {
-  MFEM_VERIFY(f.densityFes != nullptr,
-              "PreparedMappedGravitySourceOperator requires the density "
-              "finite-element space.");
-  return mean_field::field::make_field_dof_map<mean_field::field::Density,
-                                               DomainSchema>(*f.densityFes)
-      .reduced_size();
-}
+    int get_operator_width(const mean_field::fem::FEM &f) {
+        MFEM_VERIFY(
+            f.densityFes != nullptr, "PreparedMappedGravitySourceOperator requires the density "
+                                     "finite-element space."
+        );
+        return mean_field::field::make_field_dof_map<mean_field::field::Density, DomainSchema>(*f.densityFes)
+            .reduced_size();
+    }
 
-void true_to_local(const mfem::ParFiniteElementSpace &finite_element_space,
-                   const mfem::Vector &true_vector,
-                   mfem::Vector &local_vector) {
-  local_vector.SetSize(finite_element_space.GetVSize());
+    void true_to_local(
+        const mfem::ParFiniteElementSpace &finite_element_space,
+        const mfem::Vector &true_vector,
+        mfem::Vector &local_vector
+    ) {
+        local_vector.SetSize(finite_element_space.GetVSize());
 
-  const mfem::Operator *prolongation =
-      finite_element_space.GetProlongationMatrix();
+        const mfem::Operator *prolongation = finite_element_space.GetProlongationMatrix();
 
-  if (prolongation != nullptr) {
-    prolongation->Mult(true_vector, local_vector);
-  } else {
-    local_vector = true_vector;
-  }
-}
+        if (prolongation != nullptr) {
+            prolongation->Mult(true_vector, local_vector);
+        } else {
+            local_vector = true_vector;
+        }
+    }
 
-void local_to_true(const mfem::ParFiniteElementSpace &finite_element_space,
-                   const mfem::Vector &local_vector,
-                   mfem::Vector &true_vector) {
-  MFEM_VERIFY(local_vector.Size() == finite_element_space.GetVSize(),
-              "Local vector has the wrong size.");
+    void local_to_true(
+        const mfem::ParFiniteElementSpace &finite_element_space,
+        const mfem::Vector &local_vector,
+        mfem::Vector &true_vector
+    ) {
+        MFEM_VERIFY(local_vector.Size() == finite_element_space.GetVSize(), "Local vector has the wrong size.");
 
-  true_vector.SetSize(finite_element_space.GetTrueVSize());
-  true_vector = 0.0;
+        true_vector.SetSize(finite_element_space.GetTrueVSize());
+        true_vector                        = 0.0;
 
-  const mfem::Operator *prolongation =
-      finite_element_space.GetProlongationMatrix();
+        const mfem::Operator *prolongation = finite_element_space.GetProlongationMatrix();
 
-  if (prolongation != nullptr) {
-    prolongation->MultTranspose(local_vector, true_vector);
-  } else {
-    true_vector = local_vector;
-  }
-}
+        if (prolongation != nullptr) {
+            prolongation->MultTranspose(local_vector, true_vector);
+        } else {
+            true_vector = local_vector;
+        }
+    }
 
-const mfem::IntegrationRule &
-get_source_rule(const mean_field::fem::FEM &f,
-                const mfem::FiniteElement &density_element,
-                const mfem::FiniteElement &potential_element,
-                const mfem::ElementTransformation &transformation) {
-  using GravityField = mean_field::field::Field<mean_field::field::Gravity>;
-  MFEM_VERIFY(density_element.GetOrder() ==
-                  mean_field::field::Density::Scalar::familyOrder,
-              "The prepared source trial element does not match the registered "
-              "density field.");
-  MFEM_VERIFY(potential_element.GetOrder() ==
-                  mean_field::field::Gravity::Potential::familyOrder,
-              "The prepared source test element does not match the registered "
-              "gravity potential.");
-  const mean_field::quadrature::Query query = GravityField::make_query<
-      mean_field::field::Gravity::Form::SourceProjection>(
-      mean_field::quadrature::QuadratureRole::discretization,
-      transformation.OrderW(), {}, mean_field::utils::DOMAINS::STELLAR,
-      mean_field::quadrature::MappingKind::general);
+    const mfem::IntegrationRule &get_source_rule(
+        const mean_field::fem::FEM &f,
+        const mfem::FiniteElement &density_element,
+        const mfem::FiniteElement &potential_element,
+        const mfem::ElementTransformation &transformation
+    ) {
+        using GravityField = mean_field::field::Field<mean_field::field::Gravity>;
+        MFEM_VERIFY(
+            density_element.GetOrder() == mean_field::field::Density::Scalar::familyOrder,
+            "The prepared source trial element does not match the registered "
+            "density field."
+        );
+        MFEM_VERIFY(
+            potential_element.GetOrder() == mean_field::field::Gravity::Potential::familyOrder,
+            "The prepared source test element does not match the registered "
+            "gravity potential."
+        );
+        const mean_field::quadrature::Query query =
+            GravityField::make_query<mean_field::field::Gravity::Form::SourceProjection>(
+                mean_field::quadrature::QuadratureRole::discretization, transformation.OrderW(), {},
+                mean_field::utils::DOMAINS::STELLAR, mean_field::quadrature::MappingKind::general
+            );
 
-  return *f.quadratureFactory->get(query, transformation.GetGeometryType())
-              .integration_rule;
-}
+        return *f.quadratureFactory->get(query, transformation.GetGeometryType()).integration_rule;
+    }
 
-class FrozenMappedGravitySourceCoefficient final : public mfem::Coefficient {
-public:
-  FrozenMappedGravitySourceCoefficient(
-      const mean_field::fem::FEM &f,
-      const mean_field::mapping::DomainMapper &domain_mapper,
-      const mfem::Vector &displacement_true)
-      : m_fem(f), m_domain_mapper(domain_mapper),
-        m_workspace(domain_mapper.GetDimension()) {
-    true_to_local(*m_fem.displacementFes, displacement_true,
-                  m_displacement_local);
-  }
+    class FrozenMappedGravitySourceCoefficient final : public mfem::Coefficient {
+    public:
+        FrozenMappedGravitySourceCoefficient(
+            const mean_field::fem::FEM &f,
+            const mean_field::mapping::DomainMapper &domain_mapper,
+            const mfem::Vector &displacement_true
+        )
+            : m_fem(f),
+              m_domain_mapper(domain_mapper),
+              m_workspace(domain_mapper.GetDimension()) {
+            true_to_local(*m_fem.displacementFes, displacement_true, m_displacement_local);
+        }
 
-  double Eval(mfem::ElementTransformation &transformation,
-              const mfem::IntegrationPoint &integration_point) override {
-    transformation.SetIntPoint(&integration_point);
+        double Eval(
+            mfem::ElementTransformation &transformation,
+            const mfem::IntegrationPoint &integration_point
+        ) override {
+            transformation.SetIntPoint(&integration_point);
 
-    const int element_id = transformation.ElementNo;
-    MFEM_VERIFY(element_id >= 0 && element_id < m_fem.mesh->GetNE(),
+            const int element_id = transformation.ElementNo;
+            MFEM_VERIFY(
+                element_id >= 0 && element_id < m_fem.mesh->GetNE(),
                 "Mapped gravity source coefficient received an invalid element "
-                "ID.");
-    if (DomainSchema::template attribute_belongs_to<
-            mean_field::utils::domain::Vacuum>(transformation.Attribute)) {
-      return 0.0;
-    }
+                "ID."
+            );
+            if (DomainSchema::template attribute_belongs_to<mean_field::utils::domain::Vacuum>(
+                    transformation.Attribute
+                )) {
+                return 0.0;
+            }
 
-    LoadElement(element_id);
-    const mean_field::mapping::ElementMappingData mapping_data{
-        .displacement = *m_displacement_data,
-        .compactification = *m_compactification_data};
+            LoadElement(element_id);
+            const mean_field::mapping::ElementMappingData mapping_data{
+                .displacement = *m_displacement_data, .compactification = *m_compactification_data
+            };
 
-    mean_field::mapping::VolumeMappingContext mapping_context;
+            mean_field::mapping::VolumeMappingContext mapping_context;
 
-    const mean_field::mapping::MappingStatus status =
-        m_domain_mapper.EvaluateVolume(mapping_data, transformation,
-                                       integration_point, m_workspace,
-                                       mapping_context);
+            const mean_field::mapping::MappingStatus status = m_domain_mapper.EvaluateVolume(
+                mapping_data, transformation, integration_point, m_workspace, mapping_context
+            );
 
-    if (status != mean_field::mapping::MappingStatus::valid) {
-      const mfem::FiniteElement &displacement_element =
-          *m_fem.displacementFes->GetFE(element_id);
-      const mfem::FiniteElement &compactification_element =
-          *m_fem.compactificationFes->GetFE(element_id);
+            if (status != mean_field::mapping::MappingStatus::valid) {
+                const mfem::FiniteElement &displacement_element     = *m_fem.displacementFes->GetFE(element_id);
+                const mfem::FiniteElement &compactification_element = *m_fem.compactificationFes->GetFE(element_id);
 
-      mfem::Vector displacement_shape(displacement_element.GetDof());
-      mfem::Vector compactification_shape(compactification_element.GetDof());
-      mfem::Vector reference_position(m_domain_mapper.GetDimension());
-      mfem::Vector displacement_value(m_domain_mapper.GetDimension());
+                mfem::Vector displacement_shape(displacement_element.GetDof());
+                mfem::Vector compactification_shape(compactification_element.GetDof());
+                mfem::Vector reference_position(m_domain_mapper.GetDimension());
+                mfem::Vector displacement_value(m_domain_mapper.GetDimension());
 
-      displacement_element.CalcShape(integration_point, displacement_shape);
-      compactification_element.CalcShape(integration_point,
-                                         compactification_shape);
-      transformation.Transform(integration_point, reference_position);
-      m_displacement_data->GetDofMatrix().MultTranspose(displacement_shape,
-                                                        displacement_value);
+                displacement_element.CalcShape(integration_point, displacement_shape);
+                compactification_element.CalcShape(integration_point, compactification_shape);
+                transformation.Transform(integration_point, reference_position);
+                m_displacement_data->GetDofMatrix().MultTranspose(displacement_shape, displacement_value);
 
-      const double compactification_coordinate =
-          m_compactification_data->GetDofs() * compactification_shape;
+                const double compactification_coordinate = m_compactification_data->GetDofs() * compactification_shape;
 
-      MFEM_ABORT(
-          "Stateless domain mapping failed while preparing the "
-          "gravity "
-          "source operator."
-          << "\nMapping status = " << static_cast<int>(status)
-          << "\nElement ID = " << element_id
-          << "\nElement attribute = " << transformation.Attribute
-          << "\nIntegration-point index = " << integration_point.index
-          << "\nIntegration point = <" << integration_point.x << ", "
-          << integration_point.y << ", " << integration_point.z << ">"
-          << "\nReference position = <" << reference_position(0) << ", "
-          << reference_position(1) << ", " << reference_position(2) << ">"
-          << "\nReference radius = " << reference_position.Norml2()
-          << "\nDisplacement value = <" << displacement_value(0) << ", "
-          << displacement_value(1) << ", " << displacement_value(2) << ">"
-          << "\nDisplacement magnitude = " << displacement_value.Norml2()
-          << "\nCompactification coordinate = " << compactification_coordinate
-          << "\nDisplacement ordering = "
-          << static_cast<int>(m_fem.displacementFes->GetOrdering()));
-    }
-    const double mapping_determinant =
-        mapping_context.mapping.mapping_determinant;
-    MFEM_VERIFY(std::isfinite(mapping_determinant) && mapping_determinant > 0.0,
+                MFEM_ABORT(
+                    "Stateless domain mapping failed while preparing the "
+                    "gravity "
+                    "source operator."
+                    << "\nMapping status = " << static_cast<int>(status) << "\nElement ID = " << element_id
+                    << "\nElement attribute = " << transformation.Attribute
+                    << "\nIntegration-point index = " << integration_point.index << "\nIntegration point = <"
+                    << integration_point.x << ", " << integration_point.y << ", " << integration_point.z << ">"
+                    << "\nReference position = <" << reference_position(0) << ", " << reference_position(1) << ", "
+                    << reference_position(2) << ">"
+                    << "\nReference radius = " << reference_position.Norml2() << "\nDisplacement value = <"
+                    << displacement_value(0) << ", " << displacement_value(1) << ", " << displacement_value(2) << ">"
+                    << "\nDisplacement magnitude = " << displacement_value.Norml2()
+                    << "\nCompactification coordinate = " << compactification_coordinate
+                    << "\nDisplacement ordering = " << static_cast<int>(m_fem.displacementFes->GetOrdering())
+                );
+            }
+            const double mapping_determinant = mapping_context.mapping.mapping_determinant;
+            MFEM_VERIFY(
+                std::isfinite(mapping_determinant) && mapping_determinant > 0.0,
                 "Prepared gravity source operator encountered a non-positive "
                 "or "
-                "non-finite mapping determinant.");
+                "non-finite mapping determinant."
+            );
 
-    return 4.0 * std::numbers::pi * mean_field::utils::G * mapping_determinant;
-  }
+            return 4.0 * std::numbers::pi * mean_field::utils::G * mapping_determinant;
+        }
 
-private:
-  void LoadElement(const int element_id) {
-    if (element_id == m_cached_element_id) {
-      return;
-    }
+    private:
+        void LoadElement(const int element_id) {
+            if (element_id == m_cached_element_id) {
+                return;
+            }
 
-    const mfem::FiniteElement &displacement_element =
-        *m_fem.displacementFes->GetFE(element_id);
-    const mfem::FiniteElement &compactification_element =
-        *m_fem.compactificationFes->GetFE(element_id);
+            const mfem::FiniteElement &displacement_element     = *m_fem.displacementFes->GetFE(element_id);
+            const mfem::FiniteElement &compactification_element = *m_fem.compactificationFes->GetFE(element_id);
 
-    mfem::DofTransformation *displacement_dof_transformation =
-        m_fem.displacementFes->GetElementVDofs(element_id, m_displacement_dofs);
-    mfem::DofTransformation *compactification_dof_transformation =
-        m_fem.compactificationFes->GetElementDofs(element_id,
-                                                  m_compactification_dofs);
+            mfem::DofTransformation *displacement_dof_transformation =
+                m_fem.displacementFes->GetElementVDofs(element_id, m_displacement_dofs);
+            mfem::DofTransformation *compactification_dof_transformation =
+                m_fem.compactificationFes->GetElementDofs(element_id, m_compactification_dofs);
 
-    m_displacement_local.GetSubVector(m_displacement_dofs,
-                                      m_element_displacement);
-    m_fem.compactificationCoordinate->GetSubVector(m_compactification_dofs,
-                                                   m_element_compactification);
+            m_displacement_local.GetSubVector(m_displacement_dofs, m_element_displacement);
+            m_fem.compactificationCoordinate->GetSubVector(m_compactification_dofs, m_element_compactification);
 
-    if (displacement_dof_transformation != nullptr) {
-      displacement_dof_transformation->InvTransformPrimal(
-          m_element_displacement);
-    }
+            if (displacement_dof_transformation != nullptr) {
+                displacement_dof_transformation->InvTransformPrimal(m_element_displacement);
+            }
 
-    if (compactification_dof_transformation != nullptr) {
-      compactification_dof_transformation->InvTransformPrimal(
-          m_element_compactification);
-    }
+            if (compactification_dof_transformation != nullptr) {
+                compactification_dof_transformation->InvTransformPrimal(m_element_compactification);
+            }
 
-    m_displacement_data =
-        std::make_unique<mean_field::mapping::ElementDisplacementData>(
-            mean_field::mapping::ElementDisplacementDataFromElementVDofs(
-                displacement_element, m_element_displacement));
+            m_displacement_data = std::make_unique<mean_field::mapping::ElementDisplacementData>(
+                mean_field::mapping::ElementDisplacementDataFromElementVDofs(
+                    displacement_element, m_element_displacement
+                )
+            );
 
-    m_compactification_data =
-        std::make_unique<mean_field::mapping::ElementCompactificationData>(
-            compactification_element, m_element_compactification);
+            m_compactification_data = std::make_unique<mean_field::mapping::ElementCompactificationData>(
+                compactification_element, m_element_compactification
+            );
 
-    m_cached_element_id = element_id;
-  }
+            m_cached_element_id = element_id;
+        }
 
-  const mean_field::fem::FEM &m_fem;
-  const mean_field::mapping::DomainMapper &m_domain_mapper;
+        const mean_field::fem::FEM &m_fem;
+        const mean_field::mapping::DomainMapper &m_domain_mapper;
 
-  mfem::Vector m_displacement_local;
+        mfem::Vector m_displacement_local;
 
-  mfem::Array<int> m_displacement_dofs;
-  mfem::Array<int> m_compactification_dofs;
+        mfem::Array<int> m_displacement_dofs;
+        mfem::Array<int> m_compactification_dofs;
 
-  mfem::Vector m_element_displacement;
-  mfem::Vector m_element_compactification;
+        mfem::Vector m_element_displacement;
+        mfem::Vector m_element_compactification;
 
-  std::unique_ptr<mean_field::mapping::ElementDisplacementData>
-      m_displacement_data;
-  std::unique_ptr<mean_field::mapping::ElementCompactificationData>
-      m_compactification_data;
+        std::unique_ptr<mean_field::mapping::ElementDisplacementData> m_displacement_data;
+        std::unique_ptr<mean_field::mapping::ElementCompactificationData> m_compactification_data;
 
-  mean_field::mapping::DomainMapper::Workspace m_workspace;
-  int m_cached_element_id{-1};
-};
+        mean_field::mapping::DomainMapper::Workspace m_workspace;
+        int m_cached_element_id{-1};
+    };
 } // namespace
 
 namespace mean_field::operators {
-PreparedMappedGravitySourceOperator::PreparedMappedGravitySourceOperator(
-    const fem::FEM &f, const mapping::DomainMapper &domain_mapper)
-    : Operator(get_operator_height(f), get_operator_width(f)), m_fem(f),
-      m_domain_mapper(domain_mapper),
-      m_density_map(field::make_field_dof_map<field::Density, DomainSchema>(
-          *f.densityFes)),
-      m_potential_map(field::make_field_dof_map<field::Gravity, DomainSchema>(
-          *f.gravityPotentialFes)),
-      m_displacement_map(
-          field::make_field_dof_map<field::Displacement, DomainSchema>(
-              *f.displacementFes)) {
-  MFEM_VERIFY(f.mesh != nullptr,
-              "PreparedMappedGravitySourceOperator requires a mesh.");
-  MFEM_VERIFY(f.densityFes != nullptr,
-              "PreparedMappedGravitySourceOperator requires the density "
-              "finite-element space.");
-  MFEM_VERIFY(f.gravityPotentialFes != nullptr,
-              "PreparedMappedGravitySourceOperator requires the "
-              "gravity-potential "
-              "finite-element space.");
-  MFEM_VERIFY(f.displacementFes != nullptr,
-              "PreparedMappedGravitySourceOperator requires "
-              "the displacement finite-element space.");
-  MFEM_VERIFY(
-      f.compactificationFes != nullptr,
-      "PreparedMappedGravitySourceOperator requires the compactification "
-      "finite-element space.");
-  MFEM_VERIFY(
-      f.compactificationCoordinate != nullptr,
-      "PreparedMappedGravitySourceOperator requires the compactification "
-      "coordinate.");
-  MFEM_VERIFY(f.quadratureFactory != nullptr,
-              "PreparedMappedGravitySourceOperator "
-              "requires the quadrature-rule factory.");
-  MFEM_VERIFY(domain_mapper.GetDimension() == f.mesh->Dimension(),
-              "The stateless domain-mapper dimension does not match the mesh "
-              "dimension.");
+    PreparedMappedGravitySourceOperator::PreparedMappedGravitySourceOperator(
+        const fem::FEM &f,
+        const mapping::DomainMapper &domain_mapper
+    )
+        : Operator(
+              get_operator_height(f),
+              get_operator_width(f)
+          ),
+          m_fem(f),
+          m_domain_mapper(domain_mapper),
+          m_density_map(
+              field::make_field_dof_map<
+                  field::Density,
+                  DomainSchema>(*f.densityFes)
+          ),
+          m_potential_map(
+              field::make_field_dof_map<
+                  field::Gravity,
+                  DomainSchema>(*f.gravityPotentialFes)
+          ),
+          m_displacement_map(
+              field::make_field_dof_map<
+                  field::Displacement,
+                  DomainSchema>(*f.displacementFes)
+          ) {
+        MFEM_VERIFY(f.mesh != nullptr, "PreparedMappedGravitySourceOperator requires a mesh.");
+        MFEM_VERIFY(
+            f.densityFes != nullptr, "PreparedMappedGravitySourceOperator requires the density "
+                                     "finite-element space."
+        );
+        MFEM_VERIFY(
+            f.gravityPotentialFes != nullptr, "PreparedMappedGravitySourceOperator requires the "
+                                              "gravity-potential "
+                                              "finite-element space."
+        );
+        MFEM_VERIFY(
+            f.displacementFes != nullptr, "PreparedMappedGravitySourceOperator requires "
+                                          "the displacement finite-element space."
+        );
+        MFEM_VERIFY(
+            f.compactificationFes != nullptr, "PreparedMappedGravitySourceOperator requires the compactification "
+                                              "finite-element space."
+        );
+        MFEM_VERIFY(
+            f.compactificationCoordinate != nullptr,
+            "PreparedMappedGravitySourceOperator requires the compactification "
+            "coordinate."
+        );
+        MFEM_VERIFY(
+            f.quadratureFactory != nullptr, "PreparedMappedGravitySourceOperator "
+                                            "requires the quadrature-rule factory."
+        );
+        MFEM_VERIFY(
+            domain_mapper.GetDimension() == f.mesh->Dimension(),
+            "The stateless domain-mapper dimension does not match the mesh "
+            "dimension."
+        );
 
-  m_stellar_marker =
-      utils::domain::make_attribute_marker<utils::domain::Stellar,
-                                           DomainSchema>(*f.mesh);
-}
-
-void PreparedMappedGravitySourceOperator::Prepare(
-    const mfem::Vector &displacement) {
-  MFEM_VERIFY(displacement.Size() == m_displacement_map.reduced_size(),
-              "PreparedMappedGravitySourceOperator received a displacement "
-              "vector "
-              "with the wrong size.");
-
-  for (int i = 0; i < displacement.Size(); ++i) {
-    MFEM_VERIFY(std::isfinite(displacement(i)),
-                "PreparedMappedGravitySourceOperator received a non-finite "
-                "displacement value.");
-  }
-
-  m_is_prepared = false;
-  m_displacement_true.SetSize(m_displacement_map.full_size());
-  m_displacement_map.scatter(displacement, m_displacement_true);
-  m_elements.clear();
-  m_elements.reserve(m_fem.mesh->GetNE());
-
-  FrozenMappedGravitySourceCoefficient source_coefficient(
-      m_fem, m_domain_mapper, m_displacement_true);
-
-  for (int element_id = 0; element_id < m_fem.mesh->GetNE(); ++element_id) {
-    const int attribute = m_fem.mesh->GetAttribute(element_id);
-
-    if (attribute <= 0 || attribute > m_stellar_marker.Size() ||
-        m_stellar_marker[attribute - 1] == 0) {
-      continue;
+        m_stellar_marker = utils::domain::make_attribute_marker<utils::domain::Stellar, DomainSchema>(*f.mesh);
     }
 
-    m_elements.emplace_back();
-    ElementPAData &data = m_elements.back();
+    void PreparedMappedGravitySourceOperator::Prepare(const mfem::Vector &displacement) {
+        MFEM_VERIFY(
+            displacement.Size() == m_displacement_map.reduced_size(),
+            "PreparedMappedGravitySourceOperator received a displacement "
+            "vector "
+            "with the wrong size."
+        );
 
-    data.element_id = element_id;
+        for (int i = 0; i < displacement.Size(); ++i) {
+            MFEM_VERIFY(
+                std::isfinite(displacement(i)), "PreparedMappedGravitySourceOperator received a non-finite "
+                                                "displacement value."
+            );
+        }
 
-    data.density_dof_transformation =
-        m_fem.densityFes->GetElementDofs(element_id, data.density_dofs);
+        m_is_prepared = false;
+        m_displacement_true.SetSize(m_displacement_map.full_size());
+        m_displacement_map.scatter(displacement, m_displacement_true);
+        m_elements.clear();
+        m_elements.reserve(m_fem.mesh->GetNE());
 
-    data.potential_dof_transformation =
-        m_fem.gravityPotentialFes->GetElementDofs(element_id,
-                                                  data.potential_dofs);
+        FrozenMappedGravitySourceCoefficient source_coefficient(m_fem, m_domain_mapper, m_displacement_true);
 
-    const mfem::FiniteElement &density_element =
-        *m_fem.densityFes->GetFE(element_id);
+        for (int element_id = 0; element_id < m_fem.mesh->GetNE(); ++element_id) {
+            const int attribute = m_fem.mesh->GetAttribute(element_id);
 
-    const mfem::FiniteElement &potential_element =
-        *m_fem.gravityPotentialFes->GetFE(element_id);
+            if (attribute <= 0 || attribute > m_stellar_marker.Size() || m_stellar_marker[attribute - 1] == 0) {
+                continue;
+            }
 
-    mfem::ElementTransformation &transformation =
-        *m_fem.mesh->GetElementTransformation(element_id);
+            m_elements.emplace_back();
+            ElementPAData &data             = m_elements.back();
 
-    const mfem::IntegrationRule &integration_rule = get_source_rule(
-        m_fem, density_element, potential_element, transformation);
+            data.element_id                 = element_id;
 
-    const int quadrature_point_count = integration_rule.GetNPoints();
+            data.density_dof_transformation = m_fem.densityFes->GetElementDofs(element_id, data.density_dofs);
 
-    const int density_dof_count = density_element.GetDof();
+            data.potential_dof_transformation =
+                m_fem.gravityPotentialFes->GetElementDofs(element_id, data.potential_dofs);
 
-    const int potential_dof_count = potential_element.GetDof();
+            const mfem::FiniteElement &density_element   = *m_fem.densityFes->GetFE(element_id);
 
-    data.density_basis.SetSize(quadrature_point_count, density_dof_count);
+            const mfem::FiniteElement &potential_element = *m_fem.gravityPotentialFes->GetFE(element_id);
 
-    data.potential_basis.SetSize(quadrature_point_count, potential_dof_count);
+            mfem::ElementTransformation &transformation  = *m_fem.mesh->GetElementTransformation(element_id);
 
-    data.quadrature_data.SetSize(quadrature_point_count);
+            const mfem::IntegrationRule &integration_rule =
+                get_source_rule(m_fem, density_element, potential_element, transformation);
 
-    mfem::Vector density_shape(density_dof_count);
-    mfem::Vector potential_shape(potential_dof_count);
+            const int quadrature_point_count = integration_rule.GetNPoints();
 
-    for (int quadrature_point = 0; quadrature_point < quadrature_point_count;
-         ++quadrature_point) {
-      const mfem::IntegrationPoint &integration_point =
-          integration_rule.IntPoint(quadrature_point);
+            const int density_dof_count      = density_element.GetDof();
 
-      transformation.SetIntPoint(&integration_point);
+            const int potential_dof_count    = potential_element.GetDof();
 
-      // CalcPhysShape matches the scalar mixed-mass discretization,
-      // including the finite-element map type.
-      density_element.CalcPhysShape(transformation, density_shape);
+            data.density_basis.SetSize(quadrature_point_count, density_dof_count);
 
-      potential_element.CalcPhysShape(transformation, potential_shape);
+            data.potential_basis.SetSize(quadrature_point_count, potential_dof_count);
 
-      for (int i = 0; i < density_dof_count; ++i) {
-        data.density_basis(quadrature_point, i) = density_shape(i);
-      }
+            data.quadrature_data.SetSize(quadrature_point_count);
 
-      for (int i = 0; i < potential_dof_count; ++i) {
-        data.potential_basis(quadrature_point, i) = potential_shape(i);
-      }
+            mfem::Vector density_shape(density_dof_count);
+            mfem::Vector potential_shape(potential_dof_count);
 
-      const double coefficient_value =
-          source_coefficient.Eval(transformation, integration_point);
+            for (int quadrature_point = 0; quadrature_point < quadrature_point_count; ++quadrature_point) {
+                const mfem::IntegrationPoint &integration_point = integration_rule.IntPoint(quadrature_point);
 
-      transformation.SetIntPoint(&integration_point);
+                transformation.SetIntPoint(&integration_point);
 
-      const double quadrature_value = integration_point.weight *
-                                      transformation.Weight() *
-                                      coefficient_value;
+                // CalcPhysShape matches the scalar mixed-mass discretization,
+                // including the finite-element map type.
+                density_element.CalcPhysShape(transformation, density_shape);
 
-      MFEM_VERIFY(std::isfinite(quadrature_value) && quadrature_value > 0.0,
-                  "Prepared gravity source operator encountered invalid "
-                  "quadrature data on element "
-                      << element_id << ", quadrature point " << quadrature_point
-                      << ".");
+                potential_element.CalcPhysShape(transformation, potential_shape);
 
-      data.quadrature_data(quadrature_point) = quadrature_value;
+                for (int i = 0; i < density_dof_count; ++i) {
+                    data.density_basis(quadrature_point, i) = density_shape(i);
+                }
+
+                for (int i = 0; i < potential_dof_count; ++i) {
+                    data.potential_basis(quadrature_point, i) = potential_shape(i);
+                }
+
+                const double coefficient_value = source_coefficient.Eval(transformation, integration_point);
+
+                transformation.SetIntPoint(&integration_point);
+
+                const double quadrature_value = integration_point.weight * transformation.Weight() * coefficient_value;
+
+                MFEM_VERIFY(
+                    std::isfinite(quadrature_value) && quadrature_value > 0.0,
+                    "Prepared gravity source operator encountered invalid "
+                    "quadrature data on element "
+                        << element_id << ", quadrature point " << quadrature_point << "."
+                );
+
+                data.quadrature_data(quadrature_point) = quadrature_value;
+            }
+        }
+
+        MFEM_VERIFY(!m_elements.empty(), "PreparedMappedGravitySourceOperator found no stellar elements.");
+
+        m_is_prepared = true;
+        ++m_preparation_count;
     }
-  }
+    void PreparedMappedGravitySourceOperator::Mult(
+        const mfem::Vector &density,
+        mfem::Vector &action
+    ) const {
+        MFEM_VERIFY(
+            m_is_prepared, "PreparedMappedGravitySourceOperator must be prepared before "
+                           "Mult is called."
+        );
 
-  MFEM_VERIFY(!m_elements.empty(),
-              "PreparedMappedGravitySourceOperator found no stellar elements.");
+        MFEM_VERIFY(
+            density.Size() == Width(), "PreparedMappedGravitySourceOperator received a density vector "
+                                       "with the wrong size."
+        );
 
-  m_is_prepared = true;
-  ++m_preparation_count;
-}
-void PreparedMappedGravitySourceOperator::Mult(const mfem::Vector &density,
-                                               mfem::Vector &action) const {
-  MFEM_VERIFY(m_is_prepared,
-              "PreparedMappedGravitySourceOperator must be prepared before "
-              "Mult is called.");
+        m_density_true.SetSize(m_density_map.full_size());
+        m_density_map.scatter(density, m_density_true);
 
-  MFEM_VERIFY(density.Size() == Width(),
-              "PreparedMappedGravitySourceOperator received a density vector "
-              "with the wrong size.");
+        mfem::Vector density_local;
 
-  m_density_true.SetSize(m_density_map.full_size());
-  m_density_map.scatter(density, m_density_true);
+        true_to_local(*m_fem.densityFes, m_density_true, density_local);
 
-  mfem::Vector density_local;
+        mfem::Vector local_action(m_fem.gravityPotentialFes->GetVSize());
+        local_action = 0.0;
 
-  true_to_local(*m_fem.densityFes, m_density_true, density_local);
+        mfem::Vector element_density;
+        mfem::Vector quadrature_density;
+        mfem::Vector element_action;
 
-  mfem::Vector local_action(m_fem.gravityPotentialFes->GetVSize());
-  local_action = 0.0;
+        for (const ElementPAData &data : m_elements) {
+            density_local.GetSubVector(data.density_dofs, element_density);
 
-  mfem::Vector element_density;
-  mfem::Vector quadrature_density;
-  mfem::Vector element_action;
+            if (data.density_dof_transformation != nullptr) {
+                data.density_dof_transformation->InvTransformPrimal(element_density);
+            }
 
-  for (const ElementPAData &data : m_elements) {
-    density_local.GetSubVector(data.density_dofs, element_density);
+            quadrature_density.SetSize(data.quadrature_data.Size());
 
-    if (data.density_dof_transformation != nullptr) {
-      data.density_dof_transformation->InvTransformPrimal(element_density);
+            // B_density * x_e
+            data.density_basis.Mult(element_density, quadrature_density);
+
+            // D * B_density * x_e
+            for (int q = 0; q < quadrature_density.Size(); ++q) {
+                quadrature_density(q) *= data.quadrature_data(q);
+            }
+
+            element_action.SetSize(data.potential_dofs.Size());
+
+            // B_potential^T * D * B_density * x_e
+            data.potential_basis.MultTranspose(quadrature_density, element_action);
+
+            if (data.potential_dof_transformation != nullptr) {
+                data.potential_dof_transformation->TransformDual(element_action);
+            }
+
+            local_action.AddElementVector(data.potential_dofs, element_action);
+        }
+
+        local_to_true(*m_fem.gravityPotentialFes, local_action, m_action_true);
+        action.SetSize(Height());
+        m_potential_map.gather(m_action_true, action);
     }
 
-    quadrature_density.SetSize(data.quadrature_data.Size());
+    void PreparedMappedGravitySourceOperator::MultTranspose(
+        const mfem::Vector &potential,
+        mfem::Vector &action
+    ) const {
+        MFEM_VERIFY(
+            m_is_prepared, "PreparedMappedGravitySourceOperator must be prepared before "
+                           "MultTranspose is called."
+        );
 
-    // B_density * x_e
-    data.density_basis.Mult(element_density, quadrature_density);
+        MFEM_VERIFY(
+            potential.Size() == Height(), "PreparedMappedGravitySourceOperator received a potential vector "
+                                          "with the wrong size."
+        );
 
-    // D * B_density * x_e
-    for (int q = 0; q < quadrature_density.Size(); ++q) {
-      quadrature_density(q) *= data.quadrature_data(q);
+        m_potential_true.SetSize(m_potential_map.full_size());
+        m_potential_map.scatter(potential, m_potential_true);
+
+        mfem::Vector potential_local;
+
+        true_to_local(*m_fem.gravityPotentialFes, m_potential_true, potential_local);
+
+        mfem::Vector local_action(m_fem.densityFes->GetVSize());
+        local_action = 0.0;
+
+        mfem::Vector element_potential;
+        mfem::Vector quadrature_potential;
+        mfem::Vector element_action;
+
+        for (const ElementPAData &data : m_elements) {
+            potential_local.GetSubVector(data.potential_dofs, element_potential);
+
+            if (data.potential_dof_transformation != nullptr) {
+                data.potential_dof_transformation->InvTransformPrimal(element_potential);
+            }
+
+            quadrature_potential.SetSize(data.quadrature_data.Size());
+
+            data.potential_basis.Mult(element_potential, quadrature_potential);
+
+            for (int q = 0; q < quadrature_potential.Size(); ++q) {
+                quadrature_potential(q) *= data.quadrature_data(q);
+            }
+
+            element_action.SetSize(data.density_dofs.Size());
+
+            data.density_basis.MultTranspose(quadrature_potential, element_action);
+
+            if (data.density_dof_transformation != nullptr) {
+                data.density_dof_transformation->TransformDual(element_action);
+            }
+
+            local_action.AddElementVector(data.density_dofs, element_action);
+        }
+
+        local_to_true(*m_fem.densityFes, local_action, m_action_true);
+        action.SetSize(Width());
+        m_density_map.gather(m_action_true, action);
+    }
+    bool PreparedMappedGravitySourceOperator::IsPrepared() const noexcept {
+        return m_is_prepared;
     }
 
-    element_action.SetSize(data.potential_dofs.Size());
-
-    // B_potential^T * D * B_density * x_e
-    data.potential_basis.MultTranspose(quadrature_density, element_action);
-
-    if (data.potential_dof_transformation != nullptr) {
-      data.potential_dof_transformation->TransformDual(element_action);
+    std::uint64_t PreparedMappedGravitySourceOperator::GetPreparationCount() const noexcept {
+        return m_preparation_count;
     }
 
-    local_action.AddElementVector(data.potential_dofs, element_action);
-  }
-
-  local_to_true(*m_fem.gravityPotentialFes, local_action, m_action_true);
-  action.SetSize(Height());
-  m_potential_map.gather(m_action_true, action);
-}
-
-void PreparedMappedGravitySourceOperator::MultTranspose(
-    const mfem::Vector &potential, mfem::Vector &action) const {
-  MFEM_VERIFY(m_is_prepared,
-              "PreparedMappedGravitySourceOperator must be prepared before "
-              "MultTranspose is called.");
-
-  MFEM_VERIFY(potential.Size() == Height(),
-              "PreparedMappedGravitySourceOperator received a potential vector "
-              "with the wrong size.");
-
-  m_potential_true.SetSize(m_potential_map.full_size());
-  m_potential_map.scatter(potential, m_potential_true);
-
-  mfem::Vector potential_local;
-
-  true_to_local(*m_fem.gravityPotentialFes, m_potential_true, potential_local);
-
-  mfem::Vector local_action(m_fem.densityFes->GetVSize());
-  local_action = 0.0;
-
-  mfem::Vector element_potential;
-  mfem::Vector quadrature_potential;
-  mfem::Vector element_action;
-
-  for (const ElementPAData &data : m_elements) {
-    potential_local.GetSubVector(data.potential_dofs, element_potential);
-
-    if (data.potential_dof_transformation != nullptr) {
-      data.potential_dof_transformation->InvTransformPrimal(element_potential);
+    const field::FieldDofMap &PreparedMappedGravitySourceOperator::GetDensityMap() const noexcept {
+        return m_density_map;
     }
 
-    quadrature_potential.SetSize(data.quadrature_data.Size());
-
-    data.potential_basis.Mult(element_potential, quadrature_potential);
-
-    for (int q = 0; q < quadrature_potential.Size(); ++q) {
-      quadrature_potential(q) *= data.quadrature_data(q);
+    const field::FieldDofMap &PreparedMappedGravitySourceOperator::GetPotentialMap() const noexcept {
+        return m_potential_map;
     }
 
-    element_action.SetSize(data.density_dofs.Size());
-
-    data.density_basis.MultTranspose(quadrature_potential, element_action);
-
-    if (data.density_dof_transformation != nullptr) {
-      data.density_dof_transformation->TransformDual(element_action);
+    const field::FieldDofMap &PreparedMappedGravitySourceOperator::GetDisplacementMap() const noexcept {
+        return m_displacement_map;
     }
-
-    local_action.AddElementVector(data.density_dofs, element_action);
-  }
-
-  local_to_true(*m_fem.densityFes, local_action, m_action_true);
-  action.SetSize(Width());
-  m_density_map.gather(m_action_true, action);
-}
-bool PreparedMappedGravitySourceOperator::IsPrepared() const noexcept {
-  return m_is_prepared;
-}
-
-std::uint64_t
-PreparedMappedGravitySourceOperator::GetPreparationCount() const noexcept {
-  return m_preparation_count;
-}
-
-const field::FieldDofMap &
-PreparedMappedGravitySourceOperator::GetDensityMap() const noexcept {
-  return m_density_map;
-}
-
-const field::FieldDofMap &
-PreparedMappedGravitySourceOperator::GetPotentialMap() const noexcept {
-  return m_potential_map;
-}
-
-const field::FieldDofMap &
-PreparedMappedGravitySourceOperator::GetDisplacementMap() const noexcept {
-  return m_displacement_map;
-}
 } // namespace mean_field::operators

libmeanfield/impl/operators/prepared_hdiv_mass.cpp

@@ -8,405 +8,413 @@ module mean_field;
 import :operators.prepared_hdiv_mass;
 
 namespace {
-using DomainSchema = mean_field::utils::domain::CoreEnvelopeVacuumDomainSchema;
+    using DomainSchema = mean_field::utils::domain::CoreEnvelopeVacuumDomainSchema;
 
-int get_operator_size(const mean_field::fem::FEM &f) {
-  MFEM_VERIFY(f.gravityFluxFes != nullptr,
-              "PreparedMappedHDivMassOperator requires the "
-              "gravity-gradient finite-element space.");
-  return mean_field::field::make_field_dof_map<mean_field::field::Gravity,
-                                               DomainSchema>(*f.gravityFluxFes)
-      .reduced_size();
-}
-
-void true_to_local(const mfem::ParFiniteElementSpace &finite_element_space,
-                   const mfem::Vector &true_vector,
-                   mfem::Vector &local_vector) {
-  local_vector.SetSize(finite_element_space.GetVSize());
-
-  const mfem::Operator *prolongation =
-      finite_element_space.GetProlongationMatrix();
-
-  if (prolongation != nullptr) {
-    prolongation->Mult(true_vector, local_vector);
-  } else {
-    local_vector = true_vector;
-  }
-}
-
-int find_representative_element(const mean_field::fem::FEM &f,
-                                const mfem::Array<int> &marker) {
-  for (int element_id = 0; element_id < f.mesh->GetNE(); ++element_id) {
-    const int attribute = f.mesh->GetAttribute(element_id);
-
-    if (attribute > 0 && attribute <= marker.Size() &&
-        marker[attribute - 1] != 0) {
-      return element_id;
-    }
-  }
-
-  return -1;
-}
-
-void validate_uniform_domain_discretization(
-    const mean_field::fem::FEM &f, const mfem::Array<int> &marker,
-    const int representative_element_id) {
-  const mfem::FiniteElement &representative_element =
-      *f.gravityFluxFes->GetFE(representative_element_id);
-  const mfem::ElementTransformation &representative_transformation =
-      *f.mesh->GetElementTransformation(representative_element_id);
-
-  for (int element_id = 0; element_id < f.mesh->GetNE(); ++element_id) {
-    const int attribute = f.mesh->GetAttribute(element_id);
-
-    if (attribute <= 0 || attribute > marker.Size() ||
-        marker[attribute - 1] == 0) {
-      continue;
+    int get_operator_size(const mean_field::fem::FEM &f) {
+        MFEM_VERIFY(
+            f.gravityFluxFes != nullptr, "PreparedMappedHDivMassOperator requires the "
+                                         "gravity-gradient finite-element space."
+        );
+        return mean_field::field::make_field_dof_map<mean_field::field::Gravity, DomainSchema>(*f.gravityFluxFes)
+            .reduced_size();
     }
 
-    const mfem::FiniteElement &element = *f.gravityFluxFes->GetFE(element_id);
-    const mfem::ElementTransformation &transformation =
-        *f.mesh->GetElementTransformation(element_id);
+    void true_to_local(
+        const mfem::ParFiniteElementSpace &finite_element_space,
+        const mfem::Vector &true_vector,
+        mfem::Vector &local_vector
+    ) {
+        local_vector.SetSize(finite_element_space.GetVSize());
 
-    MFEM_VERIFY(element.GetGeomType() == representative_element.GetGeomType(),
+        const mfem::Operator *prolongation = finite_element_space.GetProlongationMatrix();
+
+        if (prolongation != nullptr) {
+            prolongation->Mult(true_vector, local_vector);
+        } else {
+            local_vector = true_vector;
+        }
+    }
+
+    int find_representative_element(
+        const mean_field::fem::FEM &f,
+        const mfem::Array<int> &marker
+    ) {
+        for (int element_id = 0; element_id < f.mesh->GetNE(); ++element_id) {
+            const int attribute = f.mesh->GetAttribute(element_id);
+
+            if (attribute > 0 && attribute <= marker.Size() && marker[attribute - 1] != 0) {
+                return element_id;
+            }
+        }
+
+        return -1;
+    }
+
+    void validate_uniform_domain_discretization(
+        const mean_field::fem::FEM &f,
+        const mfem::Array<int> &marker,
+        const int representative_element_id
+    ) {
+        const mfem::FiniteElement &representative_element = *f.gravityFluxFes->GetFE(representative_element_id);
+        const mfem::ElementTransformation &representative_transformation =
+            *f.mesh->GetElementTransformation(representative_element_id);
+
+        for (int element_id = 0; element_id < f.mesh->GetNE(); ++element_id) {
+            const int attribute = f.mesh->GetAttribute(element_id);
+
+            if (attribute <= 0 || attribute > marker.Size() || marker[attribute - 1] == 0) {
+                continue;
+            }
+
+            const mfem::FiniteElement &element                = *f.gravityFluxFes->GetFE(element_id);
+            const mfem::ElementTransformation &transformation = *f.mesh->GetElementTransformation(element_id);
+
+            MFEM_VERIFY(
+                element.GetGeomType() == representative_element.GetGeomType(),
                 "Prepared H(div) mass domains currently require a uniform "
                 "element "
-                "geometry.");
-    MFEM_VERIFY(element.GetOrder() == representative_element.GetOrder(),
+                "geometry."
+            );
+            MFEM_VERIFY(
+                element.GetOrder() == representative_element.GetOrder(),
                 "Prepared H(div) mass domains currently require a uniform "
-                "finite-element order.");
-    MFEM_VERIFY(transformation.OrderW() ==
-                    representative_transformation.OrderW(),
+                "finite-element order."
+            );
+            MFEM_VERIFY(
+                transformation.OrderW() == representative_transformation.OrderW(),
                 "Prepared H(div) mass domains currently require a uniform "
-                "geometry-weight order.");
-  }
-}
-
-class FrozenMappedHDivMassCoefficient final : public mfem::MatrixCoefficient {
-public:
-  FrozenMappedHDivMassCoefficient(
-      const mean_field::fem::FEM &f,
-      const mean_field::mapping::DomainMapper &domain_mapper,
-      const mfem::Vector &displacement_true, bool elevates_vacuum)
-      : MatrixCoefficient(domain_mapper.GetDimension()), m_fem(f),
-        m_domain_mapper(domain_mapper),
-        m_workspace(domain_mapper.GetDimension()),
-        m_elevates_vacuum(elevates_vacuum) {
-    true_to_local(*m_fem.displacementFes, displacement_true,
-                  m_displacement_local);
-  }
-
-  void Eval(mfem::DenseMatrix &mass_tensor,
-            mfem::ElementTransformation &transformation,
-            const mfem::IntegrationPoint &integration_point) override {
-    transformation.SetIntPoint(&integration_point);
-
-    const int element_id = transformation.ElementNo;
-    MFEM_VERIFY(
-        element_id >= 0 && element_id < m_fem.mesh->GetNE(),
-        "Mapped H(div) mass coefficient received an invalid element ID.");
-
-    const bool element_is_vacuum = DomainSchema::template attribute_belongs_to<
-        mean_field::utils::domain::Vacuum>(transformation.Attribute);
-
-    if (element_is_vacuum != m_elevates_vacuum) {
-      mass_tensor.SetSize(m_domain_mapper.GetDimension());
-      mass_tensor = 0.0;
-      return;
+                "geometry-weight order."
+            );
+        }
     }
 
-    LoadElement(element_id);
+    class FrozenMappedHDivMassCoefficient final : public mfem::MatrixCoefficient {
+    public:
+        FrozenMappedHDivMassCoefficient(
+            const mean_field::fem::FEM &f,
+            const mean_field::mapping::DomainMapper &domain_mapper,
+            const mfem::Vector &displacement_true,
+            bool elevates_vacuum
+        )
+            : MatrixCoefficient(domain_mapper.GetDimension()),
+              m_fem(f),
+              m_domain_mapper(domain_mapper),
+              m_workspace(domain_mapper.GetDimension()),
+              m_elevates_vacuum(elevates_vacuum) {
+            true_to_local(*m_fem.displacementFes, displacement_true, m_displacement_local);
+        }
 
-    const mean_field::mapping::ElementMappingData mapping_data{
-        .displacement = *m_displacement_data,
-        .compactification = *m_compactification_data};
+        void Eval(
+            mfem::DenseMatrix &mass_tensor,
+            mfem::ElementTransformation &transformation,
+            const mfem::IntegrationPoint &integration_point
+        ) override {
+            transformation.SetIntPoint(&integration_point);
 
-    mean_field::mapping::VolumeMappingContext mapping_context;
+            const int element_id = transformation.ElementNo;
+            MFEM_VERIFY(
+                element_id >= 0 && element_id < m_fem.mesh->GetNE(),
+                "Mapped H(div) mass coefficient received an invalid element ID."
+            );
 
-    const mean_field::mapping::MappingStatus status =
-        m_domain_mapper.EvaluateVolume(mapping_data, transformation,
-                                       integration_point, m_workspace,
-                                       mapping_context);
+            const bool element_is_vacuum =
+                DomainSchema::template attribute_belongs_to<mean_field::utils::domain::Vacuum>(
+                    transformation.Attribute
+                );
 
-    MFEM_VERIFY(status == mean_field::mapping::MappingStatus::valid,
+            if (element_is_vacuum != m_elevates_vacuum) {
+                mass_tensor.SetSize(m_domain_mapper.GetDimension());
+                mass_tensor = 0.0;
+                return;
+            }
+
+            LoadElement(element_id);
+
+            const mean_field::mapping::ElementMappingData mapping_data{
+                .displacement = *m_displacement_data, .compactification = *m_compactification_data
+            };
+
+            mean_field::mapping::VolumeMappingContext mapping_context;
+
+            const mean_field::mapping::MappingStatus status = m_domain_mapper.EvaluateVolume(
+                mapping_data, transformation, integration_point, m_workspace, mapping_context
+            );
+
+            MFEM_VERIFY(
+                status == mean_field::mapping::MappingStatus::valid,
                 "Stateless domain mapping failed while preparing the H(div) "
                 "mass "
                 "operator. Mapping status = "
-                    << static_cast<int>(status)
-                    << ", element ID = " << element_id
+                    << static_cast<int>(status) << ", element ID = " << element_id
                     << ", element attribute = " << transformation.Attribute
-                    << ", coefficient domain = "
-                    << (m_elevates_vacuum ? "vacuum" : "stellar"));
+                    << ", coefficient domain = " << (m_elevates_vacuum ? "vacuum" : "stellar")
+            );
 
-    const mfem::DenseMatrix &mapping_jacobian =
-        mapping_context.mapping.mapping_jacobian;
-    const double mapping_determinant =
-        mapping_context.mapping.mapping_determinant;
+            const mfem::DenseMatrix &mapping_jacobian = mapping_context.mapping.mapping_jacobian;
+            const double mapping_determinant          = mapping_context.mapping.mapping_determinant;
 
-    MFEM_VERIFY(std::isfinite(mapping_determinant) && mapping_determinant > 0.0,
+            MFEM_VERIFY(
+                std::isfinite(mapping_determinant) && mapping_determinant > 0.0,
                 "Prepared H(div) mass operator encountered a non-positive or "
-                "non-finite mapping determinant.");
+                "non-finite mapping determinant."
+            );
 
-    mfem::MultAtB(mapping_jacobian, mapping_jacobian, mass_tensor);
-    mass_tensor *= 1.0 / mapping_determinant;
-  }
+            mfem::MultAtB(mapping_jacobian, mapping_jacobian, mass_tensor);
+            mass_tensor *= 1.0 / mapping_determinant;
+        }
 
-private:
-  void LoadElement(const int element_id) {
-    if (element_id == m_cached_element_id) {
-      return;
-    }
+    private:
+        void LoadElement(const int element_id) {
+            if (element_id == m_cached_element_id) {
+                return;
+            }
 
-    const mfem::FiniteElement &displacement_element =
-        *m_fem.displacementFes->GetFE(element_id);
-    const mfem::FiniteElement &compactification_element =
-        *m_fem.compactificationFes->GetFE(element_id);
+            const mfem::FiniteElement &displacement_element     = *m_fem.displacementFes->GetFE(element_id);
+            const mfem::FiniteElement &compactification_element = *m_fem.compactificationFes->GetFE(element_id);
 
-    mfem::DofTransformation *displacement_dof_transformation =
-        m_fem.displacementFes->GetElementVDofs(element_id, m_displacement_dofs);
-    mfem::DofTransformation *compactification_dof_transformation =
-        m_fem.compactificationFes->GetElementDofs(element_id,
-                                                  m_compactification_dofs);
+            mfem::DofTransformation *displacement_dof_transformation =
+                m_fem.displacementFes->GetElementVDofs(element_id, m_displacement_dofs);
+            mfem::DofTransformation *compactification_dof_transformation =
+                m_fem.compactificationFes->GetElementDofs(element_id, m_compactification_dofs);
 
-    m_displacement_local.GetSubVector(m_displacement_dofs,
-                                      m_element_displacement);
-    m_fem.compactificationCoordinate->GetSubVector(m_compactification_dofs,
-                                                   m_element_compactification);
+            m_displacement_local.GetSubVector(m_displacement_dofs, m_element_displacement);
+            m_fem.compactificationCoordinate->GetSubVector(m_compactification_dofs, m_element_compactification);
 
-    if (displacement_dof_transformation != nullptr) {
-      displacement_dof_transformation->InvTransformPrimal(
-          m_element_displacement);
-    }
+            if (displacement_dof_transformation != nullptr) {
+                displacement_dof_transformation->InvTransformPrimal(m_element_displacement);
+            }
 
-    if (compactification_dof_transformation != nullptr) {
-      compactification_dof_transformation->InvTransformPrimal(
-          m_element_compactification);
-    }
+            if (compactification_dof_transformation != nullptr) {
+                compactification_dof_transformation->InvTransformPrimal(m_element_compactification);
+            }
 
-    m_displacement_data =
-        std::make_unique<mean_field::mapping::ElementDisplacementData>(
-            mean_field::mapping::ElementDisplacementDataFromElementVDofs(
-                displacement_element, m_element_displacement));
+            m_displacement_data = std::make_unique<mean_field::mapping::ElementDisplacementData>(
+                mean_field::mapping::ElementDisplacementDataFromElementVDofs(
+                    displacement_element, m_element_displacement
+                )
+            );
 
-    m_compactification_data =
-        std::make_unique<mean_field::mapping::ElementCompactificationData>(
-            compactification_element, m_element_compactification);
+            m_compactification_data = std::make_unique<mean_field::mapping::ElementCompactificationData>(
+                compactification_element, m_element_compactification
+            );
 
-    m_cached_element_id = element_id;
-  }
+            m_cached_element_id = element_id;
+        }
 
-  const mean_field::fem::FEM &m_fem;
-  const mean_field::mapping::DomainMapper &m_domain_mapper;
+        const mean_field::fem::FEM &m_fem;
+        const mean_field::mapping::DomainMapper &m_domain_mapper;
 
-  mfem::Vector m_displacement_local;
+        mfem::Vector m_displacement_local;
 
-  mfem::Array<int> m_displacement_dofs;
-  mfem::Array<int> m_compactification_dofs;
+        mfem::Array<int> m_displacement_dofs;
+        mfem::Array<int> m_compactification_dofs;
 
-  mfem::Vector m_element_displacement;
-  mfem::Vector m_element_compactification;
+        mfem::Vector m_element_displacement;
+        mfem::Vector m_element_compactification;
 
-  std::unique_ptr<mean_field::mapping::ElementDisplacementData>
-      m_displacement_data;
-  std::unique_ptr<mean_field::mapping::ElementCompactificationData>
-      m_compactification_data;
+        std::unique_ptr<mean_field::mapping::ElementDisplacementData> m_displacement_data;
+        std::unique_ptr<mean_field::mapping::ElementCompactificationData> m_compactification_data;
 
-  mean_field::mapping::DomainMapper::Workspace m_workspace;
-  int m_cached_element_id{-1};
-  bool m_elevates_vacuum;
-};
+        mean_field::mapping::DomainMapper::Workspace m_workspace;
+        int m_cached_element_id{-1};
+        bool m_elevates_vacuum;
+    };
 } // namespace
 
 namespace mean_field::operators {
-PreparedMappedHDivMassOperator::PreparedMappedHDivMassOperator(
-    const fem::FEM &f, const mapping::DomainMapper &domain_mapper)
-    : Operator(get_operator_size(f)), m_fem(f), m_domain_mapper(domain_mapper),
-      m_flux_map(field::make_field_dof_map<field::Gravity, DomainSchema>(
-          *f.gravityFluxFes)),
-      m_displacement_map(
-          field::make_field_dof_map<field::Displacement, DomainSchema>(
-              *f.displacementFes)) {
-  MFEM_VERIFY(f.mesh != nullptr,
-              "PreparedMappedHDivMassOperator requires a mesh.");
-  MFEM_VERIFY(f.gravityFluxFes != nullptr,
-              "PreparedMappedHDivMassOperator requires the "
-              "gravity-gradient finite-element space.");
-  MFEM_VERIFY(f.displacementFes != nullptr,
-              "PreparedMappedHDivMassOperator requires the "
-              "displacement finite-element space.");
-  MFEM_VERIFY(f.compactificationFes != nullptr,
-              "PreparedMappedHDivMassOperator requires the compactification "
-              "finite-element space.");
-  MFEM_VERIFY(f.compactificationCoordinate != nullptr,
-              "PreparedMappedHDivMassOperator requires the compactification "
-              "coordinate.");
-  MFEM_VERIFY(f.quadratureFactory != nullptr,
-              "PreparedMappedHDivMassOperator requires the quadrature-rule "
-              "factory.");
-  MFEM_VERIFY(domain_mapper.GetDimension() == f.mesh->Dimension(),
-              "The stateless domain-mapper dimension does not match the mesh "
-              "dimension.");
+    PreparedMappedHDivMassOperator::PreparedMappedHDivMassOperator(
+        const fem::FEM &f,
+        const mapping::DomainMapper &domain_mapper
+    )
+        : Operator(get_operator_size(f)),
+          m_fem(f),
+          m_domain_mapper(domain_mapper),
+          m_flux_map(
+              field::make_field_dof_map<
+                  field::Gravity,
+                  DomainSchema>(*f.gravityFluxFes)
+          ),
+          m_displacement_map(
+              field::make_field_dof_map<
+                  field::Displacement,
+                  DomainSchema>(*f.displacementFes)
+          ) {
+        MFEM_VERIFY(f.mesh != nullptr, "PreparedMappedHDivMassOperator requires a mesh.");
+        MFEM_VERIFY(
+            f.gravityFluxFes != nullptr, "PreparedMappedHDivMassOperator requires the "
+                                         "gravity-gradient finite-element space."
+        );
+        MFEM_VERIFY(
+            f.displacementFes != nullptr, "PreparedMappedHDivMassOperator requires the "
+                                          "displacement finite-element space."
+        );
+        MFEM_VERIFY(
+            f.compactificationFes != nullptr, "PreparedMappedHDivMassOperator requires the compactification "
+                                              "finite-element space."
+        );
+        MFEM_VERIFY(
+            f.compactificationCoordinate != nullptr, "PreparedMappedHDivMassOperator requires the compactification "
+                                                     "coordinate."
+        );
+        MFEM_VERIFY(
+            f.quadratureFactory != nullptr, "PreparedMappedHDivMassOperator requires the quadrature-rule "
+                                            "factory."
+        );
+        MFEM_VERIFY(
+            domain_mapper.GetDimension() == f.mesh->Dimension(),
+            "The stateless domain-mapper dimension does not match the mesh "
+            "dimension."
+        );
 
-  m_stellar_marker =
-      utils::domain::make_attribute_marker<utils::domain::Stellar,
-                                           DomainSchema>(*f.mesh);
-  m_vacuum_marker =
-      utils::domain::make_attribute_marker<utils::domain::Vacuum, DomainSchema>(
-          *f.mesh);
+        m_stellar_marker = utils::domain::make_attribute_marker<utils::domain::Stellar, DomainSchema>(*f.mesh);
+        m_vacuum_marker  = utils::domain::make_attribute_marker<utils::domain::Vacuum, DomainSchema>(*f.mesh);
 
-  const int stellar_element_id =
-      find_representative_element(f, m_stellar_marker);
-  const int vacuum_element_id = find_representative_element(f, m_vacuum_marker);
+        const int stellar_element_id = find_representative_element(f, m_stellar_marker);
+        const int vacuum_element_id  = find_representative_element(f, m_vacuum_marker);
 
-  MFEM_VERIFY(stellar_element_id >= 0,
-              "PreparedMappedHDivMassOperator requires "
-              "at least one stellar element.");
-  MFEM_VERIFY(vacuum_element_id >= 0,
-              "PreparedMappedHDivMassOperator requires at "
-              "least one compactified vacuum element.");
+        MFEM_VERIFY(
+            stellar_element_id >= 0, "PreparedMappedHDivMassOperator requires "
+                                     "at least one stellar element."
+        );
+        MFEM_VERIFY(
+            vacuum_element_id >= 0, "PreparedMappedHDivMassOperator requires at "
+                                    "least one compactified vacuum element."
+        );
 
-  validate_uniform_domain_discretization(f, m_stellar_marker,
-                                         stellar_element_id);
-  validate_uniform_domain_discretization(f, m_vacuum_marker, vacuum_element_id);
-}
+        validate_uniform_domain_discretization(f, m_stellar_marker, stellar_element_id);
+        validate_uniform_domain_discretization(f, m_vacuum_marker, vacuum_element_id);
+    }
 
-void PreparedMappedHDivMassOperator::Prepare(const mfem::Vector &displacement) {
-  MFEM_VERIFY(displacement.Size() == m_displacement_map.reduced_size(),
-              "PreparedMappedHDivMassOperator received a displacement vector "
-              "with "
-              "the wrong size.");
+    void PreparedMappedHDivMassOperator::Prepare(const mfem::Vector &displacement) {
+        MFEM_VERIFY(
+            displacement.Size() == m_displacement_map.reduced_size(),
+            "PreparedMappedHDivMassOperator received a displacement vector "
+            "with "
+            "the wrong size."
+        );
 
-  for (int i = 0; i < displacement.Size(); ++i) {
-    MFEM_VERIFY(std::isfinite(displacement(i)),
-                "PreparedMappedHDivMassOperator received a non-finite "
-                "displacement "
-                "value.");
-  }
+        for (int i = 0; i < displacement.Size(); ++i) {
+            MFEM_VERIFY(
+                std::isfinite(displacement(i)), "PreparedMappedHDivMassOperator received a non-finite "
+                                                "displacement "
+                                                "value."
+            );
+        }
 
-  m_displacement_true.SetSize(m_displacement_map.full_size());
-  m_displacement_map.scatter(displacement, m_displacement_true);
+        m_displacement_true.SetSize(m_displacement_map.full_size());
+        m_displacement_map.scatter(displacement, m_displacement_true);
 
-  const int stellar_element_id =
-      find_representative_element(m_fem, m_stellar_marker);
-  const int vacuum_element_id =
-      find_representative_element(m_fem, m_vacuum_marker);
+        const int stellar_element_id                        = find_representative_element(m_fem, m_stellar_marker);
+        const int vacuum_element_id                         = find_representative_element(m_fem, m_vacuum_marker);
 
-  const mfem::FiniteElement &stellar_element =
-      *m_fem.gravityFluxFes->GetFE(stellar_element_id);
-  const mfem::FiniteElement &vacuum_element =
-      *m_fem.gravityFluxFes->GetFE(vacuum_element_id);
+        const mfem::FiniteElement &stellar_element          = *m_fem.gravityFluxFes->GetFE(stellar_element_id);
+        const mfem::FiniteElement &vacuum_element           = *m_fem.gravityFluxFes->GetFE(vacuum_element_id);
 
-  mfem::ElementTransformation &stellar_transformation =
-      *m_fem.mesh->GetElementTransformation(stellar_element_id);
-  mfem::ElementTransformation &vacuum_transformation =
-      *m_fem.mesh->GetElementTransformation(vacuum_element_id);
+        mfem::ElementTransformation &stellar_transformation = *m_fem.mesh->GetElementTransformation(stellar_element_id);
+        mfem::ElementTransformation &vacuum_transformation  = *m_fem.mesh->GetElementTransformation(vacuum_element_id);
 
-  m_stellar_mass_form.reset();
-  m_vacuum_mass_form.reset();
-  m_stellar_mass_coefficient.reset();
-  m_vacuum_mass_coefficient.reset();
+        m_stellar_mass_form.reset();
+        m_vacuum_mass_form.reset();
+        m_stellar_mass_coefficient.reset();
+        m_vacuum_mass_coefficient.reset();
 
-  m_stellar_mass_coefficient =
-      std::make_unique<FrozenMappedHDivMassCoefficient>(
-          m_fem, m_domain_mapper, m_displacement_true, false);
-  m_vacuum_mass_coefficient = std::make_unique<FrozenMappedHDivMassCoefficient>(
-      m_fem, m_domain_mapper, m_displacement_true, true);
+        m_stellar_mass_coefficient =
+            std::make_unique<FrozenMappedHDivMassCoefficient>(m_fem, m_domain_mapper, m_displacement_true, false);
+        m_vacuum_mass_coefficient =
+            std::make_unique<FrozenMappedHDivMassCoefficient>(m_fem, m_domain_mapper, m_displacement_true, true);
 
-  m_stellar_mass_form =
-      std::make_unique<mfem::ParBilinearForm>(m_fem.gravityFluxFes.get());
-  m_vacuum_mass_form =
-      std::make_unique<mfem::ParBilinearForm>(m_fem.gravityFluxFes.get());
-  m_stellar_mass_form->SetAssemblyLevel(mfem::AssemblyLevel::PARTIAL);
-  m_vacuum_mass_form->SetAssemblyLevel(mfem::AssemblyLevel::PARTIAL);
+        m_stellar_mass_form = std::make_unique<mfem::ParBilinearForm>(m_fem.gravityFluxFes.get());
+        m_vacuum_mass_form  = std::make_unique<mfem::ParBilinearForm>(m_fem.gravityFluxFes.get());
+        m_stellar_mass_form->SetAssemblyLevel(mfem::AssemblyLevel::PARTIAL);
+        m_vacuum_mass_form->SetAssemblyLevel(mfem::AssemblyLevel::PARTIAL);
 
-  auto stellar_integrator = std::make_unique<mfem::VectorFEMassIntegrator>(
-      *m_stellar_mass_coefficient);
-  auto vacuum_integrator = std::make_unique<mfem::VectorFEMassIntegrator>(
-      *m_vacuum_mass_coefficient);
+        auto stellar_integrator = std::make_unique<mfem::VectorFEMassIntegrator>(*m_stellar_mass_coefficient);
+        auto vacuum_integrator  = std::make_unique<mfem::VectorFEMassIntegrator>(*m_vacuum_mass_coefficient);
 
-  m_fem.quadratureFactory->configure_gravity_hdiv_mass(
-      *stellar_integrator, quadrature::QuadratureRole::discretization,
-      stellar_element, stellar_transformation, utils::DOMAINS::STELLAR,
-      quadrature::MappingKind::general);
+        m_fem.quadratureFactory->configure_gravity_hdiv_mass(
+            *stellar_integrator, quadrature::QuadratureRole::discretization, stellar_element, stellar_transformation,
+            utils::DOMAINS::STELLAR, quadrature::MappingKind::general
+        );
 
-  m_fem.quadratureFactory->configure_gravity_hdiv_mass(
-      *vacuum_integrator, quadrature::QuadratureRole::discretization,
-      vacuum_element, vacuum_transformation, utils::DOMAINS::VACUUM,
-      quadrature::MappingKind::kelvin);
+        m_fem.quadratureFactory->configure_gravity_hdiv_mass(
+            *vacuum_integrator, quadrature::QuadratureRole::discretization, vacuum_element, vacuum_transformation,
+            utils::DOMAINS::VACUUM, quadrature::MappingKind::kelvin
+        );
 
-  m_stellar_mass_form->AddDomainIntegrator(stellar_integrator.release(),
-                                           m_stellar_marker);
-  m_vacuum_mass_form->AddDomainIntegrator(vacuum_integrator.release(),
-                                          m_vacuum_marker);
-  m_stellar_mass_form->Assemble();
-  m_vacuum_mass_form->Assemble();
+        m_stellar_mass_form->AddDomainIntegrator(stellar_integrator.release(), m_stellar_marker);
+        m_vacuum_mass_form->AddDomainIntegrator(vacuum_integrator.release(), m_vacuum_marker);
+        m_stellar_mass_form->Assemble();
+        m_vacuum_mass_form->Assemble();
 
-  m_is_prepared = true;
-  ++m_preparation_count;
-}
+        m_is_prepared = true;
+        ++m_preparation_count;
+    }
 
-void PreparedMappedHDivMassOperator::Mult(const mfem::Vector &gravity_gradient,
-                                          mfem::Vector &action) const {
-  MFEM_VERIFY(m_is_prepared, "PreparedMappedHDivMassOperator must be prepared "
-                             "before Mult is called.");
-  MFEM_VERIFY(
-      m_stellar_mass_form != nullptr && m_vacuum_mass_form != nullptr,
-      "PreparedMappedHDivMassOperator has incomplete domain mass forms.");
-  MFEM_VERIFY(
-      gravity_gradient.Size() == Width(),
-      "PreparedMappedHDivMassOperator received a gravity-gradient vector "
-      "with the wrong size.");
+    void PreparedMappedHDivMassOperator::Mult(
+        const mfem::Vector &gravity_gradient,
+        mfem::Vector &action
+    ) const {
+        MFEM_VERIFY(
+            m_is_prepared, "PreparedMappedHDivMassOperator must be prepared "
+                           "before Mult is called."
+        );
+        MFEM_VERIFY(
+            m_stellar_mass_form != nullptr && m_vacuum_mass_form != nullptr,
+            "PreparedMappedHDivMassOperator has incomplete domain mass forms."
+        );
+        MFEM_VERIFY(
+            gravity_gradient.Size() == Width(), "PreparedMappedHDivMassOperator received a gravity-gradient vector "
+                                                "with the wrong size."
+        );
 
-  m_flux_true.SetSize(m_flux_map.full_size());
-  m_action_true.SetSize(m_flux_map.full_size());
-  m_domain_action_true.SetSize(m_flux_map.full_size());
-  m_flux_map.scatter(gravity_gradient, m_flux_true);
-  m_stellar_mass_form->Mult(m_flux_true, m_action_true);
-  m_vacuum_mass_form->Mult(m_flux_true, m_domain_action_true);
-  m_action_true += m_domain_action_true;
-  action.SetSize(Height());
-  m_flux_map.gather(m_action_true, action);
-}
+        m_flux_true.SetSize(m_flux_map.full_size());
+        m_action_true.SetSize(m_flux_map.full_size());
+        m_domain_action_true.SetSize(m_flux_map.full_size());
+        m_flux_map.scatter(gravity_gradient, m_flux_true);
+        m_stellar_mass_form->Mult(m_flux_true, m_action_true);
+        m_vacuum_mass_form->Mult(m_flux_true, m_domain_action_true);
+        m_action_true += m_domain_action_true;
+        action.SetSize(Height());
+        m_flux_map.gather(m_action_true, action);
+    }
 
-void PreparedMappedHDivMassOperator::AssembleDiagonal(
-    mfem::Vector &diagonal) const {
-  mfem::Vector true_diagonal;
-  AssembleTrueDiagonal(true_diagonal);
-  diagonal.SetSize(Height());
-  m_flux_map.gather(true_diagonal, diagonal);
-}
+    void PreparedMappedHDivMassOperator::AssembleDiagonal(mfem::Vector &diagonal) const {
+        mfem::Vector true_diagonal;
+        AssembleTrueDiagonal(true_diagonal);
+        diagonal.SetSize(Height());
+        m_flux_map.gather(true_diagonal, diagonal);
+    }
 
-void PreparedMappedHDivMassOperator::AssembleTrueDiagonal(
-    mfem::Vector &diagonal) const {
-  MFEM_VERIFY(m_is_prepared, "PreparedMappedHDivMassOperator must be prepared "
-                             "before assembling its diagonal.");
-  MFEM_VERIFY(
-      m_stellar_mass_form != nullptr && m_vacuum_mass_form != nullptr,
-      "PreparedMappedHDivMassOperator has incomplete domain mass forms.");
+    void PreparedMappedHDivMassOperator::AssembleTrueDiagonal(mfem::Vector &diagonal) const {
+        MFEM_VERIFY(
+            m_is_prepared, "PreparedMappedHDivMassOperator must be prepared "
+                           "before assembling its diagonal."
+        );
+        MFEM_VERIFY(
+            m_stellar_mass_form != nullptr && m_vacuum_mass_form != nullptr,
+            "PreparedMappedHDivMassOperator has incomplete domain mass forms."
+        );
 
-  diagonal.SetSize(m_flux_map.full_size());
-  mfem::Vector domain_diagonal(m_flux_map.full_size());
-  m_stellar_mass_form->AssembleDiagonal(diagonal);
-  m_vacuum_mass_form->AssembleDiagonal(domain_diagonal);
-  diagonal += domain_diagonal;
-}
+        diagonal.SetSize(m_flux_map.full_size());
+        mfem::Vector domain_diagonal(m_flux_map.full_size());
+        m_stellar_mass_form->AssembleDiagonal(diagonal);
+        m_vacuum_mass_form->AssembleDiagonal(domain_diagonal);
+        diagonal += domain_diagonal;
+    }
 
-bool PreparedMappedHDivMassOperator::IsPrepared() const noexcept {
-  return m_is_prepared;
-}
+    bool PreparedMappedHDivMassOperator::IsPrepared() const noexcept {
+        return m_is_prepared;
+    }
 
-std::uint64_t
-PreparedMappedHDivMassOperator::GetPreparationCount() const noexcept {
-  return m_preparation_count;
-}
+    std::uint64_t PreparedMappedHDivMassOperator::GetPreparationCount() const noexcept {
+        return m_preparation_count;
+    }
 
-const field::FieldDofMap &
-PreparedMappedHDivMassOperator::GetFluxMap() const noexcept {
-  return m_flux_map;
-}
+    const field::FieldDofMap &PreparedMappedHDivMassOperator::GetFluxMap() const noexcept {
+        return m_flux_map;
+    }
 
-const field::FieldDofMap &
-PreparedMappedHDivMassOperator::GetDisplacementMap() const noexcept {
-  return m_displacement_map;
-}
+    const field::FieldDofMap &PreparedMappedHDivMassOperator::GetDisplacementMap() const noexcept {
+        return m_displacement_map;
+    }
 } // namespace mean_field::operators

libmeanfield/impl/operators/prepared_pressure_force.cpp

@@ -617,13 +617,19 @@ namespace mean_field::operators {
             data.enthalpyJacobian = 0.0;
 
             for (int quadraturePoint = 0; quadraturePoint < quadraturePointCount; ++quadraturePoint) {
-                const double enthalpy           = quadratureEnthalpy(quadraturePoint);
+                const double enthalpy = quadratureEnthalpy(quadraturePoint);
 
-                const double pressure           = m_equationOfState.pressure_from_enthalpy(enthalpy);
+                const eos::SpecificEnthalpyValue specificEnthalpy{enthalpy};
+                const double pressure =
+                    eos::evaluate<eos::quantity::Pressure>(m_equationOfState, specificEnthalpy).value();
 
-                const double pressureDerivative = m_equationOfState.pressure_derivative_from_enthalpy(enthalpy);
+                const double pressureDerivative =
+                    eos::partialDerivative<eos::quantity::Pressure, eos::quantity::SpecificEnthalpy>(
+                        m_equationOfState, specificEnthalpy
+                    )
+                        .value();
 
-                const double quadratureWeight   = data.quadratureWeights(quadraturePoint);
+                const double quadratureWeight = data.quadratureWeights(quadraturePoint);
 
                 MFEM_VERIFY(
                     std::isfinite(pressure) && std::isfinite(pressureDerivative),

libmeanfield/impl/operators/prepared_stellar_equilibrium.cpp

@@ -21,6 +21,12 @@ namespace {
         );
     }
 
+    [[nodiscard]] mfem::Vector make_computational_origin(const mfem::ParMesh &mesh) {
+        mfem::Vector origin(mesh.SpaceDimension());
+        origin = 0.0;
+        return origin;
+    }
+
     [[nodiscard]] mean_field::operators::StellarEquilibriumLayout make_layout(
         const mean_field::field::FieldDofMap &densityMap,
         const mean_field::field::FieldDofMap &displacementMap,
@@ -253,6 +259,8 @@ namespace mean_field::operators {
         field::FieldDofMap gravityFluxMap;
         field::FieldDofMap gravityPotentialMap;
         field::FieldDofMap enthalpyMap;
+        field::FieldBoundaryDofMap pressureSurfaceRows;
+        field::FieldPointDofMap centerDisplacementRows;
 
         StellarEquilibriumLayout layout;
         mfem::Array<int> gravityStateOffsets;
@@ -284,6 +292,23 @@ namespace mean_field::operators {
                       field::Enthalpy,
                       DomainSchema>(*f.enthalpyFes)
               ),
+              pressureSurfaceRows(
+                  field::make_field_boundary_dof_map<
+                      field::Enthalpy,
+                      utils::domain::StellarSurface,
+                      DomainSchema>(
+                      *f.enthalpyFes,
+                      enthalpyMap
+                  )
+              ),
+              centerDisplacementRows(
+                  field::make_field_point_dof_map<field::Displacement>(
+                      *f.displacementFes,
+                      displacementMap,
+                      make_computational_origin(*f.mesh),
+                      1.0e-12
+                  )
+              ),
               layout(make_layout(
                   densityMap,
                   displacementMap,
@@ -314,27 +339,15 @@ namespace mean_field::operators {
         fem::FEM &f,
         const mapping::DomainMapper &domainMapper,
         const eos::Polytrope &equationOfState,
-        const models::StellarModel &stellarModel
-    )
-        : PreparedStellarEquilibriumOperator(
-              f,
-              domainMapper,
-              equationOfState,
-              stellarModel.targetMass()
-          ) {
-    }
-
-    PreparedStellarEquilibriumOperator::PreparedStellarEquilibriumOperator(
-        fem::FEM &f,
-        const mapping::DomainMapper &domainMapper,
-        const eos::Polytrope &equationOfState,
-        const double targetMass
+        const double targetMass,
+        const PressureSurfaceConstraintView surfaceConstraint
     )
         : PreparedStellarEquilibriumOperator(
               f,
               domainMapper,
               equationOfState,
               targetMass,
+              surfaceConstraint,
               MakeConstructionData(f)
           ) {
     }
@@ -344,6 +357,7 @@ namespace mean_field::operators {
         const mapping::DomainMapper &domainMapper,
         const eos::Polytrope &equationOfState,
         const double targetMass,
+        const PressureSurfaceConstraintView surfaceConstraint,
         ConstructionData constructionData
     )
         : mfem::Operator(
@@ -390,6 +404,11 @@ namespace mean_field::operators {
               domainMapper,
               m_gravityContext
           ),
+          m_surfaceConstraintOperator(
+              constructionData.pressureSurfaceRows,
+              surfaceConstraint
+          ),
+          m_centeringConstraintOperator(constructionData.centerDisplacementRows),
           m_targetMass(targetMass) {
         MFEM_VERIFY(
             std::isfinite(m_targetMass) && m_targetMass > 0.0,
@@ -506,6 +525,14 @@ namespace mean_field::operators {
         report.massNormalization =
             m_massNormalizationOperator.Prepare({.targetMass = m_targetMass}, make_mass_dependencies(dependencies));
 
+        report.surfaceConstraint = m_surfaceConstraintOperator.Prepare(
+            reducedEnthalpy, !wasPrepared || dependencies.enthalpy != m_preparedDependencies.enthalpy
+        );
+
+        report.centeringConstraint = m_centeringConstraintOperator.Prepare(
+            displacement, !wasPrepared || dependencies.displacement != m_preparedDependencies.displacement
+        );
+
         const bool dependenciesChanged = !wasPrepared || dependencies != m_preparedDependencies;
         if (dependenciesChanged || report.DidAnyChildWork()) {
             AssembleResidual();
@@ -542,7 +569,9 @@ namespace mean_field::operators {
         m_gravityOperator.Mult(m_gravityState, gravity);
         m_barotropicClosureOperator.BuildResidual(closure);
         m_displacementOperator.BuildResidual(displacement);
+        m_centeringConstraintOperator.ApplyResidualRows(displacement);
         m_hydrostaticOperator.BuildResidual(hydrostatic);
+        m_surfaceConstraintOperator.ApplyResidualRows(hydrostatic);
         m_massNormalizationOperator.BuildResidual(mass);
 
         m_cachedResidual.SetSize(Height());
@@ -659,11 +688,13 @@ namespace mean_field::operators {
             reducedDensityDirection, displacementDirection, gravityGradientDirection, reducedEnthalpyDirection,
             displacementAction
         );
+        m_centeringConstraintOperator.ApplyJacobianRows(displacementDirection, displacementAction);
 
         m_hydrostaticOperator.ApplyCompleteJacobianAction(
             reducedEnthalpyDirection, gravityPotentialDirection, bernoulliDirection(0), displacementDirection,
             hydrostaticAction
         );
+        m_surfaceConstraintOperator.ApplyJacobianRows(reducedEnthalpyDirection, hydrostaticAction);
 
         m_massNormalizationOperator.ApplyCompleteJacobianAction(
             reducedDensityDirection, displacementDirection, massAction
@@ -712,7 +743,8 @@ namespace mean_field::operators {
     bool PreparedStellarEquilibriumOperator::IsPrepared() const noexcept {
         return m_isPrepared && m_gravityContext.IsPrepared() && m_barotropicClosureOperator.IsPrepared() &&
                m_hydrostaticOperator.IsPrepared() && m_displacementOperator.IsPrepared() &&
-               m_massNormalizationOperator.IsPrepared();
+               m_massNormalizationOperator.IsPrepared() && m_surfaceConstraintOperator.IsPrepared() &&
+               m_centeringConstraintOperator.IsPrepared();
     }
 
     double PreparedStellarEquilibriumOperator::GetTargetMass() const noexcept {
@@ -771,6 +803,16 @@ namespace mean_field::operators {
         return m_massNormalizationOperator;
     }
 
+    const PreparedPressureSurfaceConstraint &
+    PreparedStellarEquilibriumOperator::GetSurfaceConstraintOperator() const noexcept {
+        return m_surfaceConstraintOperator;
+    }
+
+    const PreparedCenteringConstraint &
+    PreparedStellarEquilibriumOperator::GetCenteringConstraintOperator() const noexcept {
+        return m_centeringConstraintOperator;
+    }
+
     void PreparedStellarEquilibriumOperator::VerifyPrepared() const {
         MFEM_VERIFY(
             IsPrepared(), "PreparedStellarEquilibriumOperator must be prepared before residual or Jacobian application."

libmeanfield/impl/physics/gravity.cpp

@@ -13,16 +13,14 @@ namespace mean_field::physics {
     ) {
         const int dim = fem.mesh->Dimension();
         mfem::DenseMatrix local_Q(dim, dim);
-        local_Q = 0.0;
+        local_Q            = 0.0;
         using DomainSchema = utils::domain::CoreEnvelopeVacuumDomainSchema;
         mapping::GridFunctionMappingEvaluator mapping_evaluator(
-            *fem.domainMapperStateless, *fem.displacement,
-            *fem.compactificationCoordinate
+            *fem.domainMapperStateless, *fem.displacement, *fem.compactificationCoordinate
         );
 
         for (int i = 0; i < fem.mesh->GetNE(); ++i) {
-            if (!DomainSchema::template attribute_belongs_to<utils::domain::Stellar>(
-                    fem.mesh->GetAttribute(i)))
+            if (!DomainSchema::template attribute_belongs_to<utils::domain::Stellar>(fem.mesh->GetAttribute(i)))
                 continue;
 
             mfem::ElementTransformation *trans = fem.mesh->GetElementTransformation(i);
@@ -40,13 +38,12 @@ namespace mean_field::physics {
 
                 mapping::VolumeMappingContext mapping_context;
                 MFEM_VERIFY(
-                    mapping_evaluator.EvaluateVolume(*trans, ip, mapping_context) ==
-                        mapping::MappingStatus::valid,
+                    mapping_evaluator.EvaluateVolume(*trans, ip, mapping_context) == mapping::MappingStatus::valid,
                     "Quadrupole integration encountered an invalid mapping."
                 );
-                const double weight = mapping_context.quadrature.weight;
+                const double weight            = mapping_context.quadrature.weight;
 
-                const double rho_val = rho.GetValue(i, ip);
+                const double rho_val           = rho.GetValue(i, ip);
 
                 const mfem::Vector &phys_point = mapping_context.mapping.physical_position;
 
@@ -145,7 +142,7 @@ namespace mean_field::physics {
         constexpr auto gravity_poisson_residual_block =
             utils::blocks::get_residual_block<form>(utils::blocks::gravity_field.poisson_term);
 
-        using DomainSchema                   = utils::domain::CoreEnvelopeVacuumDomainSchema;
+        using DomainSchema = utils::domain::CoreEnvelopeVacuumDomainSchema;
         const field::FieldDofGridFunctionAdapter density_adapter =
             field::make_field_dof_grid_function_adapter<field::Density, DomainSchema>(*f.densityFes);
         const field::FieldDofGridFunctionAdapter displacement_adapter =
@@ -220,12 +217,8 @@ namespace mean_field::physics {
 
         GravitySolution solution(f);
 
-        gravity_flux_adapter.scatter(
-            gravity_state.GetBlock(gravity_gradient_residual_block), solution.gradPhi
-        );
-        gravity_potential_adapter.scatter(
-            gravity_state.GetBlock(gravity_poisson_residual_block), solution.phi
-        );
+        gravity_flux_adapter.scatter(gravity_state.GetBlock(gravity_gradient_residual_block), solution.gradPhi);
+        gravity_potential_adapter.scatter(gravity_state.GetBlock(gravity_poisson_residual_block), solution.phi);
 
         return solution;
     }

libmeanfield/impl/physics/solid.cpp

@@ -9,16 +9,14 @@ namespace mean_field::physics {
         const fem::FEM &fem,
         const mfem::GridFunction &rho_ref
     ) {
-        double local_I = 0.0;
+        double local_I     = 0.0;
         using DomainSchema = utils::domain::CoreEnvelopeVacuumDomainSchema;
         mapping::GridFunctionMappingEvaluator mapping_evaluator(
-            *fem.domainMapperStateless, *fem.displacement,
-            *fem.compactificationCoordinate
+            *fem.domainMapperStateless, *fem.displacement, *fem.compactificationCoordinate
         );
 
         for (int i = 0; i < fem.mesh->GetNE(); i++) {
-            if (!DomainSchema::template attribute_belongs_to<utils::domain::Stellar>(
-                    fem.mesh->GetAttribute(i)))
+            if (!DomainSchema::template attribute_belongs_to<utils::domain::Stellar>(fem.mesh->GetAttribute(i)))
                 continue;
 
             mfem::ElementTransformation *T = fem.mesh->GetElementTransformation(i);
@@ -37,14 +35,13 @@ namespace mean_field::physics {
 
                 mapping::VolumeMappingContext mapping_context;
                 MFEM_VERIFY(
-                    mapping_evaluator.EvaluateVolume(*T, ip, mapping_context) ==
-                        mapping::MappingStatus::valid,
+                    mapping_evaluator.EvaluateVolume(*T, ip, mapping_context) == mapping::MappingStatus::valid,
                     "Moment-of-inertia integration encountered an invalid mapping."
                 );
                 const mfem::Vector &x_phys = mapping_context.mapping.physical_position;
 
-                const double r_cyl_sq = x_phys(0) * x_phys(0) + x_phys(1) * x_phys(1);
-                const double weight   = mapping_context.quadrature.weight;
+                const double r_cyl_sq      = x_phys(0) * x_phys(0) + x_phys(1) * x_phys(1);
+                const double weight        = mapping_context.quadrature.weight;
 
                 local_I += rho_hat * r_cyl_sq * weight;
             }

libmeanfield/impl/utils/domain.cpp

@@ -13,8 +13,7 @@ namespace mean_field::utils {
         const int dim = fem.mesh->Dimension();
         x_ref         = x_phys_target;
         mapping::GridFunctionMappingEvaluator mapping_evaluator(
-            *fem.domainMapperStateless, *fem.displacement,
-            *fem.compactificationCoordinate
+            *fem.domainMapperStateless, *fem.displacement, *fem.compactificationCoordinate
         );
 
         mfem::Array<int> init_elem;
@@ -39,8 +38,7 @@ namespace mean_field::utils {
 
                 mapping::MappingPointContext context;
                 MFEM_VERIFY(
-                    mapping_evaluator.EvaluatePoint(*T0, origin_ip[0], context) ==
-                        mapping::MappingStatus::valid,
+                    mapping_evaluator.EvaluatePoint(*T0, origin_ip[0], context) == mapping::MappingStatus::valid,
                     "Reference-point initialization encountered an invalid mapping."
                 );
 
@@ -104,8 +102,7 @@ namespace mean_field::utils {
             T->SetIntPoint(&ip);
 
             mapping::MappingPointContext context;
-            if (mapping_evaluator.EvaluatePoint(*T, ip, context) !=
-                mapping::MappingStatus::valid) {
+            if (mapping_evaluator.EvaluatePoint(*T, ip, context) != mapping::MappingStatus::valid) {
                 return false;
             }
             const mfem::Vector &current_x_phys = context.physical_position;

libmeanfield/impl/utils/misc.cpp

@@ -4,21 +4,25 @@ module;
 module mean_field;
 
 namespace mean_field::utils {
-DOMAINS operator|(DOMAINS lhs, DOMAINS rhs) {
-  return static_cast<DOMAINS>(static_cast<uint8_t>(lhs) |
-                              static_cast<uint8_t>(rhs));
-}
+    DOMAINS operator|(
+        DOMAINS lhs,
+        DOMAINS rhs
+    ) {
+        return static_cast<DOMAINS>(static_cast<uint8_t>(lhs) | static_cast<uint8_t>(rhs));
+    }
 
-DOMAINS operator&(DOMAINS lhs, DOMAINS rhs) {
-  return static_cast<DOMAINS>(static_cast<uint8_t>(lhs) &
-                              static_cast<uint8_t>(rhs));
-}
+    DOMAINS operator&(
+        DOMAINS lhs,
+        DOMAINS rhs
+    ) {
+        return static_cast<DOMAINS>(static_cast<uint8_t>(lhs) & static_cast<uint8_t>(rhs));
+    }
 
-int get_mesh_order(const mfem::Mesh &mesh) {
-  if (mesh.GetNodes() != nullptr) {
-    return mesh.GetNodes()->FESpace()->GetMaxElementOrder();
-  }
-  return 1;
-}
+    int get_mesh_order(const mfem::Mesh &mesh) {
+        if (mesh.GetNodes() != nullptr) {
+            return mesh.GetNodes()->FESpace()->GetMaxElementOrder();
+        }
+        return 1;
+    }
 
 } // namespace mean_field::utils

libmeanfield/interface/eos/concepts.cppm

@@ -0,0 +1,100 @@
+module;
+
+#include <concepts>
+#include <type_traits>
+
+export module mean_field:eos.concepts;
+export import :eos.relations;
+
+export namespace mean_field::eos {
+    namespace detail {
+        template <typename EquationOfState, typename RelationType> struct ImplementsRelation : std::false_type { };
+
+        template <
+            typename EquationOfState,
+            typename Output,
+            typename... Inputs>
+            struct ImplementsRelation<
+                EquationOfState,
+                Relation<
+                    Output,
+                    Inputs...>> : std::bool_constant <
+                                  requires(
+                                      const std::remove_cvref_t<EquationOfState> &equationOfState,
+                                      QuantityValue<Inputs>... inputValues
+                                  ) {
+            {equationOfState.evaluate(Relation<Output, Inputs...>{}, inputValues...)}
+                ->std::same_as<QuantityValue<Output>>;
+        }>{};
+
+        template <typename EquationOfState, typename Catalog> struct ImplementsRelationCatalog : std::false_type { };
+
+        template <typename EquationOfState, typename... Relations>
+        struct ImplementsRelationCatalog<EquationOfState, RelationCatalog<Relations...>>
+            : std::bool_constant<(ImplementsRelation<EquationOfState, Relations>::value && ...)> { };
+
+        template <typename Candidate, typename = void> struct IsEquationOfStateModel : std::false_type { };
+
+        template <typename Candidate>
+        struct IsEquationOfStateModel<Candidate, std::void_t<typename std::remove_cvref_t<Candidate>::Relations>>
+            : std::bool_constant<
+                  ValidRelationCatalog<typename std::remove_cvref_t<Candidate>::Relations> &&
+                  ImplementsRelationCatalog<
+                      std::remove_cvref_t<Candidate>,
+                      typename std::remove_cvref_t<Candidate>::Relations>::value> { };
+
+        template <typename EquationOfState, typename RelationType, typename InputQuantity>
+        struct ImplementsPartialDerivative : std::false_type { };
+
+        template <
+            typename EquationOfState,
+            typename Output,
+            typename... Inputs,
+            typename InputQuantity>
+                struct ImplementsPartialDerivative<
+                    EquationOfState,
+                    Relation<
+                        Output,
+                        Inputs...>,
+                    InputQuantity> : std::bool_constant <
+                                     (std::same_as<
+                                          InputQuantity,
+                                          Inputs> ||
+                                      ...) &&
+            requires(
+                const std::remove_cvref_t<EquationOfState> &equationOfState,
+                QuantityValue<Inputs>... inputValues
+            ) {
+            {equationOfState
+                 .partialDerivative(Relation<Output, Inputs...>{}, WithRespectTo<InputQuantity>{}, inputValues...)}
+                ->std::same_as<PartialDerivative<Output, InputQuantity>>;
+        }>{};
+    } // namespace detail
+
+    template <typename Candidate>
+    concept EquationOfStateModel = detail::IsEquationOfStateModel<Candidate>::value;
+
+    template <typename EquationOfState, typename RelationType>
+    concept SupportsRelation =
+        EquationOfStateModel<EquationOfState> && ThermodynamicRelationType<RelationType> &&
+        relationCatalogContains<typename std::remove_cvref_t<EquationOfState>::Relations, RelationType>;
+
+    template <typename EquationOfState, typename RelationType, typename InputQuantity>
+    concept SupportsPartialDerivative =
+        SupportsRelation<EquationOfState, RelationType> && ThermodynamicQuantityType<InputQuantity> &&
+        detail::ImplementsPartialDerivative<EquationOfState, RelationType, InputQuantity>::value;
+
+    template <typename Candidate>
+    concept StructureSeedEquationOfState =
+        EquationOfStateModel<Candidate> && SupportsRelation<Candidate, SpecificEnthalpyFromDensity>;
+
+    template <typename Candidate>
+    concept BarotropicClosureEquationOfState =
+        EquationOfStateModel<Candidate> && SupportsRelation<Candidate, DensityFromSpecificEnthalpy> &&
+        SupportsPartialDerivative<Candidate, DensityFromSpecificEnthalpy, quantity::SpecificEnthalpy>;
+
+    template <typename Candidate>
+    concept PressureForceEquationOfState =
+        EquationOfStateModel<Candidate> && SupportsRelation<Candidate, PressureFromSpecificEnthalpy> &&
+        SupportsPartialDerivative<Candidate, PressureFromSpecificEnthalpy, quantity::SpecificEnthalpy>;
+} // namespace mean_field::eos

libmeanfield/interface/eos/eos_base.cppm

@@ -1,16 +0,0 @@
-export module mean_field:eos.base;
-
-export namespace mean_field::eos {
-    class EquationOfState {
-    public:
-        virtual ~EquationOfState()                                                            = default;
-        [[nodiscard]] virtual double pressure_from_density(double density) const              = 0;
-        [[nodiscard]] virtual double pressure_from_enthalpy(double enthalpy) const            = 0;
-        [[nodiscard]] virtual double enthalpy_from_density(double density) const              = 0;
-        [[nodiscard]] virtual double enthalpy_from_pressure(double pressure) const            = 0;
-        [[nodiscard]] virtual double density_from_enthalpy(double enthalpy) const             = 0;
-        [[nodiscard]] virtual double density_derivative_from_enthalpy(double enthalpy) const  = 0;
-        [[nodiscard]] virtual double pressure_derivative_from_enthalpy(double enthalpy) const = 0;
-        [[nodiscard]] virtual double pressure_derivative_from_density(double density) const   = 0;
-    };
-} // namespace mean_field::eos

libmeanfield/interface/eos/evaluation.cppm

@@ -0,0 +1,90 @@
+module;
+
+#include <stdexcept>
+#include <string>
+#include <utility>
+
+export module mean_field:eos.evaluation;
+export import :eos.concepts;
+
+export namespace mean_field::eos {
+    enum class EvaluationErrorCode {
+        unsupported_relation,
+        unsupported_derivative,
+        wrong_input_count,
+        wrong_input_quantity,
+        nonfinite_input,
+        outside_domain,
+        nonfinite_result
+    };
+
+    class EvaluationError final : public std::domain_error {
+    public:
+        explicit EvaluationError(
+            const EvaluationErrorCode code,
+            std::string message
+        )
+            : std::domain_error(std::move(message)),
+              m_code(code) {
+        }
+
+        [[nodiscard]] EvaluationErrorCode code() const noexcept {
+            return m_code;
+        }
+
+    private:
+        EvaluationErrorCode m_code;
+    };
+
+    template <
+        ThermodynamicQuantityType OutputQuantity,
+        EquationOfStateModel EquationOfState,
+        QuantityValueType... InputValues>
+        requires SupportsRelation<
+            EquationOfState,
+            Relation<
+                OutputQuantity,
+                QuantityOfT<InputValues>...>>
+    [[nodiscard]] constexpr QuantityValue<OutputQuantity> evaluate(
+        const EquationOfState &equationOfState,
+        const InputValues... inputValues
+    ) noexcept(noexcept(equationOfState
+                            .evaluate(
+                                Relation<
+                                    OutputQuantity,
+                                    QuantityOfT<InputValues>...>{},
+                                inputValues...
+                            ))) {
+        return equationOfState.evaluate(Relation<OutputQuantity, QuantityOfT<InputValues>...>{}, inputValues...);
+    }
+
+    template <
+        ThermodynamicQuantityType OutputQuantity,
+        ThermodynamicQuantityType InputQuantity,
+        EquationOfStateModel EquationOfState,
+        QuantityValueType... InputValues>
+        requires SupportsPartialDerivative<
+            EquationOfState,
+            Relation<
+                OutputQuantity,
+                QuantityOfT<InputValues>...>,
+            InputQuantity>
+    [[nodiscard]] constexpr PartialDerivative<
+        OutputQuantity,
+        InputQuantity>
+    partialDerivative(
+        const EquationOfState &equationOfState,
+        const InputValues... inputValues
+    ) noexcept(noexcept(equationOfState
+                            .partialDerivative(
+                                Relation<
+                                    OutputQuantity,
+                                    QuantityOfT<InputValues>...>{},
+                                WithRespectTo<InputQuantity>{},
+                                inputValues...
+                            ))) {
+        return equationOfState.partialDerivative(
+            Relation<OutputQuantity, QuantityOfT<InputValues>...>{}, WithRespectTo<InputQuantity>{}, inputValues...
+        );
+    }
+} // namespace mean_field::eos

libmeanfield/interface/eos/polytropic.cppm

@@ -3,11 +3,18 @@ module;
 #include <format>
 #include <stdexcept>
 export module mean_field:eos.polytrope;
-export import :eos.base;
+export import :eos.evaluation;
 
 export namespace mean_field::eos {
-    class Polytrope final : public EquationOfState {
+    class Polytrope final {
     public:
+        using Relations = RelationCatalog<
+            PressureFromDensity,
+            PressureFromSpecificEnthalpy,
+            SpecificEnthalpyFromDensity,
+            SpecificEnthalpyFromPressure,
+            DensityFromSpecificEnthalpy>;
+
         Polytrope(
             const double polytropic_index,
             const double polytropic_constant
@@ -49,82 +56,128 @@ export namespace mean_field::eos {
             return m_enthalpy_scale;
         }
 
-        [[nodiscard]] double pressure_from_density(const double density) const override {
-            validate_nonnegativity(density, "density");
-            if (density == 0.0) {
-                return 0.0;
+        [[nodiscard]] PressureValue evaluate(
+            PressureFromDensity,
+            const DensityValue density
+        ) const {
+            validate_nonnegativity(density.value(), "density");
+            if (density.value() == 0.0) {
+                return PressureValue{0.0};
             }
 
-            return m_polytropic_constant * std::pow(density, 1.0 + 1.0 / m_polytropic_index);
+            return PressureValue{m_polytropic_constant * std::pow(density.value(), 1.0 + 1.0 / m_polytropic_index)};
         }
 
-        [[nodiscard]] double enthalpy_from_density(const double density) const override {
-            validate_nonnegativity(density, "density");
-            if (density == 0.0) {
-                return 0.0;
+        [[nodiscard]] SpecificEnthalpyValue evaluate(
+            SpecificEnthalpyFromDensity,
+            const DensityValue density
+        ) const {
+            validate_nonnegativity(density.value(), "density");
+            if (density.value() == 0.0) {
+                return SpecificEnthalpyValue{0.0};
             }
 
-            return m_enthalpy_scale * std::pow(density, 1.0 / m_polytropic_index);
+            return SpecificEnthalpyValue{m_enthalpy_scale * std::pow(density.value(), 1.0 / m_polytropic_index)};
         }
 
-        [[nodiscard]] double density_from_enthalpy(const double enthalpy) const override {
-            validate_finite(enthalpy, "enthalpy");
+        [[nodiscard]] DensityValue evaluate(
+            DensityFromSpecificEnthalpy,
+            const SpecificEnthalpyValue specificEnthalpy
+        ) const {
+            validate_finite(specificEnthalpy.value(), "specific enthalpy");
 
-            if (enthalpy <= 0.0) {
-                return 0.0;
+            if (specificEnthalpy.value() <= 0.0) {
+                return DensityValue{0.0};
             }
 
-            return std::pow(enthalpy / m_enthalpy_scale, m_polytropic_index);
+            return DensityValue{std::pow(specificEnthalpy.value() / m_enthalpy_scale, m_polytropic_index)};
         }
 
-        [[nodiscard]] double pressure_from_enthalpy(const double enthalpy) const override {
-            validate_finite(enthalpy, "enthalpy");
+        [[nodiscard]] PressureValue evaluate(
+            PressureFromSpecificEnthalpy,
+            const SpecificEnthalpyValue specificEnthalpy
+        ) const {
+            const DensityValue density = evaluate(DensityFromSpecificEnthalpy{}, specificEnthalpy);
 
-            if (enthalpy <= 0.0) {
-                return 0.0;
+            if (specificEnthalpy.value() <= 0.0) {
+                return PressureValue{0.0};
             }
 
-            return density_from_enthalpy(enthalpy) * enthalpy / (m_polytropic_index + 1.0);
+            return PressureValue{density.value() * specificEnthalpy.value() / (m_polytropic_index + 1.0)};
         }
 
-        [[nodiscard]] double density_derivative_from_enthalpy(const double enthalpy) const override {
-            validate_finite(enthalpy, "enthalpy");
-            if (enthalpy < 0.0) {
-                return 0.0;
+        [[nodiscard]] SpecificEnthalpyValue evaluate(
+            SpecificEnthalpyFromPressure,
+            const PressureValue pressure
+        ) const {
+            validate_nonnegativity(pressure.value(), "pressure");
+            if (pressure.value() == 0.0) {
+                return SpecificEnthalpyValue{0.0};
             }
 
-            if (enthalpy == 0.0) {
-                return m_polytropic_index == 1.0 ? 1.0 / m_enthalpy_scale : 0.0;
-            }
+            const double indexPlusOne = m_polytropic_index + 1.0;
 
-            return m_polytropic_index / m_enthalpy_scale *
-                   std::pow(enthalpy / m_enthalpy_scale, m_polytropic_index - 1.0);
+            return SpecificEnthalpyValue{
+                indexPlusOne * std::pow(m_polytropic_constant, m_polytropic_index / indexPlusOne) *
+                std::pow(pressure.value(), 1.0 / indexPlusOne)
+            };
         }
 
-        [[nodiscard]] double pressure_derivative_from_enthalpy(const double enthalpy) const override {
-            validate_finite(enthalpy, "enthalpy");
-
-            if (enthalpy <= 0.0) {
-                return 0.0;
+        [[nodiscard]] PartialDerivative<
+            quantity::Density,
+            quantity::SpecificEnthalpy>
+        partialDerivative(
+            DensityFromSpecificEnthalpy,
+            WithRespectTo<quantity::SpecificEnthalpy>,
+            const SpecificEnthalpyValue specificEnthalpy
+        ) const {
+            validate_finite(specificEnthalpy.value(), "specific enthalpy");
+            if (specificEnthalpy.value() < 0.0) {
+                return PartialDerivative<quantity::Density, quantity::SpecificEnthalpy>{0.0};
             }
 
-            return density_from_enthalpy(enthalpy);
-        }
-
-        [[nodiscard]] double pressure_derivative_from_density(const double density) const override {
-            validate_nonnegativity(density, "density");
-            if (density == 0.0) {
-                return 0.0;
+            if (specificEnthalpy.value() == 0.0) {
+                return PartialDerivative<quantity::Density, quantity::SpecificEnthalpy>{
+                    m_polytropic_index == 1.0 ? 1.0 / m_enthalpy_scale : 0.0
+                };
             }
 
-            return m_polytropic_constant * (1.0 + 1.0 / m_polytropic_index) *
-                   std::pow(density, 1.0 / m_polytropic_index);
+            return PartialDerivative<quantity::Density, quantity::SpecificEnthalpy>{
+                m_polytropic_index / m_enthalpy_scale *
+                std::pow(specificEnthalpy.value() / m_enthalpy_scale, m_polytropic_index - 1.0)
+            };
         }
 
-        [[nodiscard]] double enthalpy_from_pressure(const double pressure) const override {
-            validate_nonnegativity(pressure, "pressure");
-            const double np1 = m_polytropic_index + 1;
-            return np1 * std::pow(m_polytropic_constant, m_polytropic_index / np1) * std::pow(pressure, 1.0 / np1);
+        [[nodiscard]] PartialDerivative<
+            quantity::Pressure,
+            quantity::SpecificEnthalpy>
+        partialDerivative(
+            PressureFromSpecificEnthalpy,
+            WithRespectTo<quantity::SpecificEnthalpy>,
+            const SpecificEnthalpyValue specificEnthalpy
+        ) const {
+            const DensityValue density = evaluate(DensityFromSpecificEnthalpy{}, specificEnthalpy);
+
+            return PartialDerivative<quantity::Pressure, quantity::SpecificEnthalpy>{density.value()};
+        }
+
+        [[nodiscard]] PartialDerivative<
+            quantity::Pressure,
+            quantity::Density>
+        partialDerivative(
+            PressureFromDensity,
+            WithRespectTo<quantity::Density>,
+            const DensityValue density
+        ) const {
+            validate_nonnegativity(density.value(), "density");
+            if (density.value() == 0.0) {
+                return PartialDerivative<quantity::Pressure, quantity::Density>{0.0};
+            }
+
+            return PartialDerivative<quantity::Pressure, quantity::Density>{
+                m_polytropic_constant * (1.0 + 1.0 / m_polytropic_index) *
+                std::pow(density.value(), 1.0 / m_polytropic_index)
+            };
         }
 
     private:
@@ -133,12 +186,12 @@ export namespace mean_field::eos {
             const char *quantity
         ) {
             if (!std::isfinite(value)) {
-                throw std::domain_error(
-                    std::format(
-                        "The {} must be finite. Instead a value of {} has been "
-                        "provided",
-                        quantity, value
-                    )
+                throw EvaluationError(
+                    EvaluationErrorCode::nonfinite_input, std::format(
+                                                              "The {} must be finite. Instead a value of {} has been "
+                                                              "provided",
+                                                              quantity, value
+                                                          )
                 );
             }
         }
@@ -149,13 +202,13 @@ export namespace mean_field::eos {
         ) {
             validate_finite(value, quantity);
             if (value < 0.0) {
-                throw std::domain_error(
-                    std::format(
-                        "The {} must be non-negative. Instead a value of {} "
-                        "has been "
-                        "provided",
-                        quantity, value
-                    )
+                throw EvaluationError(
+                    EvaluationErrorCode::outside_domain, std::format(
+                                                             "The {} must be non-negative. Instead a value of {} "
+                                                             "has been "
+                                                             "provided",
+                                                             quantity, value
+                                                         )
                 );
             }
         }

libmeanfield/interface/eos/pressure_surface.cppm

@@ -0,0 +1,128 @@
+module;
+
+#include <memory>
+#include <type_traits>
+
+export module mean_field:eos.pressure_surface;
+
+export import :eos.evaluation;
+
+export namespace mean_field::eos {
+    namespace detail {
+        template <
+            ThermodynamicQuantityType InputQuantity,
+            typename SurfaceState>
+        [[nodiscard]] constexpr auto pressureSurfaceRelationInput(
+            const PressureValue targetPressure,
+            const SurfaceState &state
+        ) {
+            if constexpr (std::same_as<InputQuantity, quantity::Pressure>) {
+                return targetPressure;
+            } else {
+                return state.value(InputQuantity{});
+            }
+        }
+
+        template <typename RelationType> struct PressureSurfaceRelationOperations;
+
+        template <typename CarrierQuantity, typename... InputQuantities>
+        struct PressureSurfaceRelationOperations<Relation<CarrierQuantity, InputQuantities...>> {
+            template <
+                typename EquationOfState,
+                typename SurfaceState>
+            [[nodiscard]] static QuantityValue<CarrierQuantity> requiredCarrierValue(
+                const EquationOfState &equationOfState,
+                const PressureValue targetPressure,
+                const SurfaceState &state
+            ) {
+                return evaluate<CarrierQuantity>(
+                    equationOfState, pressureSurfaceRelationInput<InputQuantities>(targetPressure, state)...
+                );
+            }
+
+            template <
+                typename InputQuantity,
+                typename EquationOfState,
+                typename SurfaceState,
+                typename SurfaceVariation>
+            [[nodiscard]] static double inputJacobianContribution(
+                const EquationOfState &equationOfState,
+                const PressureValue targetPressure,
+                const SurfaceState &state,
+                const SurfaceVariation &variation
+            ) {
+                if constexpr (std::same_as<InputQuantity, quantity::Pressure>) {
+                    return 0.0;
+                } else {
+                    const auto derivative = partialDerivative<CarrierQuantity, InputQuantity>(
+                        equationOfState, pressureSurfaceRelationInput<InputQuantities>(targetPressure, state)...
+                    );
+                    return derivative.value() * variation.value(InputQuantity{}).value();
+                }
+            }
+
+            template <
+                typename EquationOfState,
+                typename SurfaceState,
+                typename SurfaceVariation>
+            [[nodiscard]] static double carrierCorrectionJacobianAction(
+                const EquationOfState &equationOfState,
+                const PressureValue targetPressure,
+                const SurfaceState &state,
+                const SurfaceVariation &variation
+            ) {
+                return (
+                    0.0 + ... +
+                    inputJacobianContribution<InputQuantities>(equationOfState, targetPressure, state, variation)
+                );
+            }
+        };
+    } // namespace detail
+
+    /*
+     * EOS-owned resolution of a constant-pressure condition into the carrier
+     * quantity used by an equation formulation. No field or solver concepts
+     * enter this type.
+     */
+    template <EquationOfStateModel EquationOfState, ThermodynamicRelationType SelectedRelation>
+    class ResolvedPressureSurfaceRelation final {
+    public:
+        using RelationType    = SelectedRelation;
+        using CarrierQuantity = RelationOutputT<RelationType>;
+
+        ResolvedPressureSurfaceRelation(
+            const EquationOfState &equationOfState,
+            const PressureValue targetPressure
+        ) noexcept
+            : m_equationOfState(std::addressof(equationOfState)),
+              m_targetPressure(targetPressure) {
+        }
+
+        [[nodiscard]] PressureValue targetPressure() const noexcept {
+            return m_targetPressure;
+        }
+
+        template <typename SurfaceState>
+        [[nodiscard]] QuantityValue<CarrierQuantity> requiredCarrierValue(const SurfaceState &state) const {
+            return detail::PressureSurfaceRelationOperations<RelationType>::requiredCarrierValue(
+                *m_equationOfState, m_targetPressure, state
+            );
+        }
+
+        template <
+            typename SurfaceState,
+            typename SurfaceVariation>
+        [[nodiscard]] double carrierCorrectionJacobianAction(
+            const SurfaceState &state,
+            const SurfaceVariation &variation
+        ) const {
+            return detail::PressureSurfaceRelationOperations<RelationType>::carrierCorrectionJacobianAction(
+                *m_equationOfState, m_targetPressure, state, variation
+            );
+        }
+
+    private:
+        const EquationOfState *m_equationOfState;
+        PressureValue m_targetPressure;
+    };
+} // namespace mean_field::eos

libmeanfield/interface/eos/quantities.cppm

@@ -0,0 +1,235 @@
+module;
+
+#include <compare>
+#include <concepts>
+#include <string_view>
+#include <type_traits>
+
+export module mean_field:eos.quantities;
+
+export namespace mean_field::eos {
+    struct ThermodynamicQuantity { };
+
+    template <typename Candidate>
+    concept ThermodynamicQuantityType =
+        std::same_as<Candidate, std::remove_cv_t<Candidate>> && std::derived_from<Candidate, ThermodynamicQuantity>;
+
+    namespace quantity {
+        struct Density final : ThermodynamicQuantity {
+            static constexpr std::string_view identifier = "density";
+        };
+
+        struct Pressure final : ThermodynamicQuantity {
+            static constexpr std::string_view identifier = "pressure";
+        };
+
+        struct SpecificEnthalpy final : ThermodynamicQuantity {
+            static constexpr std::string_view identifier = "specific_enthalpy";
+        };
+    } // namespace quantity
+
+    template <typename T>
+    concept Numeric = std::integral<T> || std::floating_point<T>;
+
+    template <ThermodynamicQuantityType Quantity> class QuantityValue final {
+    public:
+        explicit constexpr QuantityValue(const double value) noexcept : m_value(value) {
+        }
+
+        [[nodiscard]] constexpr double value() const noexcept {
+            return m_value;
+        }
+
+        [[nodiscard]] friend constexpr bool operator==(
+            const QuantityValue &,
+            const QuantityValue &
+        ) noexcept = default;
+
+        friend constexpr QuantityValue<Quantity> operator+(
+            const QuantityValue<Quantity> &lhs,
+            const QuantityValue<Quantity> &rhs
+        ) noexcept {
+            return QuantityValue<Quantity>{lhs.m_value + rhs.m_value};
+        }
+
+        friend constexpr QuantityValue<Quantity> operator-(
+            const QuantityValue<Quantity> &lhs,
+            const QuantityValue<Quantity> &rhs
+        ) noexcept {
+            return QuantityValue<Quantity>{lhs.m_value - rhs.m_value};
+        }
+
+        template <Numeric rhsT>
+        friend constexpr QuantityValue<Quantity> operator*(
+            const QuantityValue<Quantity> &lhs,
+            rhsT rhs
+        ) noexcept {
+            return QuantityValue<Quantity>{lhs.m_value * static_cast<double>(rhs)};
+        }
+
+        template <Numeric lhsT>
+        friend constexpr QuantityValue<Quantity> operator*(
+            lhsT lhs,
+            const QuantityValue<Quantity> &rhs
+        ) noexcept {
+            return QuantityValue<Quantity>{static_cast<double>(lhs) * rhs.m_value};
+        }
+
+        template <Numeric rhsT>
+        friend constexpr QuantityValue<Quantity> operator/(
+            const QuantityValue<Quantity> &lhs,
+            rhsT rhs
+        ) noexcept {
+            return QuantityValue<Quantity>{lhs.m_value / static_cast<double>(rhs)};
+        }
+
+        template <Numeric compT>
+        friend constexpr std::partial_ordering operator<=>(
+            const QuantityValue<Quantity> &lhs,
+            compT rhs
+        ) noexcept {
+            return lhs.m_value <=> static_cast<double>(rhs);
+        }
+
+        template <Numeric compT>
+        friend constexpr std::partial_ordering operator<=>(
+            compT lhs,
+            const QuantityValue<Quantity> &rhs
+        ) noexcept {
+            return static_cast<double>(lhs) <=> rhs.m_value;
+        }
+
+        friend constexpr std::partial_ordering operator<=>(
+            const QuantityValue<Quantity> &lhs,
+            const QuantityValue<Quantity> &rhs
+        ) noexcept {
+            return lhs.m_value <=> rhs.m_value;
+        }
+
+    private:
+        double m_value;
+    };
+
+    using DensityValue          = QuantityValue<quantity::Density>;
+    using PressureValue         = QuantityValue<quantity::Pressure>;
+    using SpecificEnthalpyValue = QuantityValue<quantity::SpecificEnthalpy>;
+
+    template <typename Candidate> struct IsQuantityValue : std::false_type { };
+
+    template <ThermodynamicQuantityType Quantity> struct IsQuantityValue<QuantityValue<Quantity>> : std::true_type { };
+
+    template <typename Candidate>
+    concept QuantityValueType = IsQuantityValue<std::remove_cvref_t<Candidate>>::value;
+
+    template <typename Candidate> struct QuantityOf;
+
+    template <ThermodynamicQuantityType Quantity> struct QuantityOf<QuantityValue<Quantity>> {
+        using Type = Quantity;
+    };
+
+    template <QuantityValueType Value> using QuantityOfT = typename QuantityOf<std::remove_cvref_t<Value>>::Type;
+
+    template <ThermodynamicQuantityType OutputQuantity, ThermodynamicQuantityType InputQuantity>
+    class PartialDerivative final {
+    public:
+        explicit constexpr PartialDerivative(const double value) noexcept : m_value(value) {
+        }
+
+        [[nodiscard]] constexpr double value() const noexcept {
+            return m_value;
+        }
+
+        friend constexpr PartialDerivative<
+            OutputQuantity,
+            InputQuantity>
+        operator+(
+            const PartialDerivative<
+                OutputQuantity,
+                InputQuantity> &lhs,
+            const PartialDerivative<
+                OutputQuantity,
+                InputQuantity> &rhs
+        ) noexcept;
+
+        friend constexpr PartialDerivative<
+            OutputQuantity,
+            InputQuantity>
+        operator-(
+            const PartialDerivative<
+                OutputQuantity,
+                InputQuantity> &lhs,
+            const PartialDerivative<
+                OutputQuantity,
+                InputQuantity> &rhs
+        ) noexcept;
+
+        template <Numeric rhsT>
+        friend constexpr PartialDerivative<
+            OutputQuantity,
+            InputQuantity>
+        operator*(
+            const PartialDerivative<
+                OutputQuantity,
+                InputQuantity> &,
+            rhsT
+        ) noexcept;
+
+        template <Numeric lhsT>
+        friend constexpr PartialDerivative<
+            OutputQuantity,
+            InputQuantity>
+        operator*(
+            lhsT,
+            const PartialDerivative<
+                OutputQuantity,
+                InputQuantity> &
+        ) noexcept;
+
+        template <Numeric rhsT>
+        friend constexpr PartialDerivative<
+            OutputQuantity,
+            InputQuantity>
+        operator/(
+            const PartialDerivative<
+                OutputQuantity,
+                InputQuantity> &,
+            rhsT
+        ) noexcept;
+
+        template <Numeric cmpT>
+        friend constexpr std::partial_ordering operator<=>(
+            const PartialDerivative<
+                OutputQuantity,
+                InputQuantity> &lhs,
+            cmpT rhs
+        ) noexcept {
+            return lhs.m_value <=> static_cast<double>(rhs);
+        }
+
+        template <Numeric cmpT>
+        friend constexpr std::partial_ordering operator<=>(
+            cmpT lhs,
+            const PartialDerivative<
+                OutputQuantity,
+                InputQuantity> &rhs
+        ) noexcept {
+            return static_cast<double>(lhs) <=> rhs.m_value;
+        }
+
+        friend constexpr std::partial_ordering operator<=>(
+            const PartialDerivative<
+                OutputQuantity,
+                InputQuantity> &lhs,
+            const PartialDerivative<
+                OutputQuantity,
+                InputQuantity> &rhs
+        ) noexcept {
+            return lhs.m_value <=> rhs.m_value;
+        }
+
+    private:
+        double m_value;
+    };
+
+    template <ThermodynamicQuantityType Quantity> struct WithRespectTo final { };
+} // namespace mean_field::eos

libmeanfield/interface/eos/relations.cppm

@@ -0,0 +1,93 @@
+module;
+
+#include <concepts>
+#include <cstddef>
+#include <tuple>
+#include <type_traits>
+
+export module mean_field:eos.relations;
+export import :eos.quantities;
+
+export namespace mean_field::eos {
+    template <typename... Quantities> struct QuantityList final { };
+
+    template <typename Output, typename... Inputs> struct Relation final {
+        using OutputQuantity                    = Output;
+        using InputQuantities                   = QuantityList<Inputs...>;
+
+        static constexpr std::size_t inputCount = sizeof...(Inputs);
+    };
+
+    template <typename... Relations> struct RelationCatalog final {
+        static constexpr std::size_t size = sizeof...(Relations);
+    };
+
+    namespace detail {
+        template <typename... Types> struct TypesAreUnique;
+
+        template <typename Candidate> struct IsThermodynamicRelation : std::false_type { };
+
+        template <typename Output, typename... Inputs>
+        struct IsThermodynamicRelation<Relation<Output, Inputs...>>
+            : std::bool_constant<
+                  ThermodynamicQuantityType<Output> && (ThermodynamicQuantityType<Inputs> && ...) &&
+                  TypesAreUnique<Inputs...>::value> { };
+
+        template <typename... Types> struct TypesAreUnique : std::true_type { };
+
+        template <typename First, typename... Remaining>
+        struct TypesAreUnique<First, Remaining...>
+            : std::bool_constant<(!std::same_as<First, Remaining> && ...) && TypesAreUnique<Remaining...>::value> { };
+
+        template <typename Candidate> struct IsValidRelationCatalog : std::false_type { };
+
+        template <typename... Relations>
+        struct IsValidRelationCatalog<RelationCatalog<Relations...>>
+            : std::bool_constant<
+                  (sizeof...(Relations) > 0) && (IsThermodynamicRelation<Relations>::value && ...) &&
+                  TypesAreUnique<Relations...>::value> { };
+
+        template <typename Catalog, typename RelationType> struct CatalogContainsRelation : std::false_type { };
+
+        template <typename... Relations, typename RelationType>
+        struct CatalogContainsRelation<RelationCatalog<Relations...>, RelationType>
+            : std::bool_constant<(std::same_as<RelationType, Relations> || ...)> { };
+
+        template <typename RelationType, typename Quantity> struct RelationContainsInput : std::false_type { };
+
+        template <typename Output, typename... Inputs, typename Quantity>
+        struct RelationContainsInput<Relation<Output, Inputs...>, Quantity>
+            : std::bool_constant<(std::same_as<Quantity, Inputs> || ...)> { };
+
+        template <std::size_t Index, typename Quantities> struct QuantityAt;
+
+        template <std::size_t Index, typename... Quantities> struct QuantityAt<Index, QuantityList<Quantities...>> {
+            using Type = std::tuple_element_t<Index, std::tuple<Quantities...>>;
+        };
+    } // namespace detail
+
+    template <typename Candidate>
+    concept ThermodynamicRelationType = detail::IsThermodynamicRelation<std::remove_cv_t<Candidate>>::value;
+
+    template <typename Candidate>
+    concept ValidRelationCatalog = detail::IsValidRelationCatalog<std::remove_cv_t<Candidate>>::value;
+
+    template <typename Catalog, typename RelationType>
+    inline constexpr bool relationCatalogContains =
+        detail::CatalogContainsRelation<std::remove_cv_t<Catalog>, std::remove_cv_t<RelationType>>::value;
+
+    template <typename RelationType, typename Quantity>
+    inline constexpr bool relationContainsInput =
+        detail::RelationContainsInput<std::remove_cv_t<RelationType>, std::remove_cv_t<Quantity>>::value;
+
+    template <ThermodynamicRelationType RelationType> using RelationOutputT = typename RelationType::OutputQuantity;
+
+    template <std::size_t Index, ThermodynamicRelationType RelationType>
+    using RelationInputT      = typename detail::QuantityAt<Index, typename RelationType::InputQuantities>::Type;
+
+    using PressureFromDensity = Relation<quantity::Pressure, quantity::Density>;
+    using PressureFromSpecificEnthalpy = Relation<quantity::Pressure, quantity::SpecificEnthalpy>;
+    using SpecificEnthalpyFromDensity  = Relation<quantity::SpecificEnthalpy, quantity::Density>;
+    using SpecificEnthalpyFromPressure = Relation<quantity::SpecificEnthalpy, quantity::Pressure>;
+    using DensityFromSpecificEnthalpy  = Relation<quantity::Density, quantity::SpecificEnthalpy>;
+} // namespace mean_field::eos

libmeanfield/interface/eos/runtime.cppm

@@ -0,0 +1,645 @@
+module;
+
+#include <array>
+#include <concepts>
+#include <cstddef>
+#include <cstdint>
+#include <expected>
+#include <memory>
+#include <span>
+#include <string>
+#include <string_view>
+#include <tuple>
+#include <type_traits>
+#include <utility>
+
+export module mean_field:eos.runtime;
+export import :eos.evaluation;
+
+export namespace mean_field::eos {
+    class ThermodynamicQuantityId final {
+    public:
+        explicit constexpr ThermodynamicQuantityId(const std::string_view name) noexcept : m_name(name) {
+        }
+
+        [[nodiscard]] constexpr std::string_view name() const noexcept {
+            return m_name;
+        }
+
+        [[nodiscard]] friend constexpr bool operator==(
+            const ThermodynamicQuantityId &,
+            const ThermodynamicQuantityId &
+        ) noexcept = default;
+
+    private:
+        std::string_view m_name;
+    };
+
+    template <typename Quantity>
+    concept RuntimeIdentifiedThermodynamicQuantity = ThermodynamicQuantityType<Quantity> && requires {
+        { Quantity::identifier } -> std::convertible_to<std::string_view>;
+    } && (std::string_view{Quantity::identifier}.size() > 0);
+
+    template <RuntimeIdentifiedThermodynamicQuantity Quantity>
+    inline constexpr ThermodynamicQuantityId thermodynamicQuantityId{std::string_view{Quantity::identifier}};
+
+    struct RuntimeQuantityValue final {
+        ThermodynamicQuantityId quantity;
+        double value;
+    };
+
+    struct RuntimeRelationDescriptor final {
+        ThermodynamicQuantityId outputQuantity;
+        std::span<const ThermodynamicQuantityId> inputQuantities;
+        std::uint64_t partialDerivativeMask;
+
+        [[nodiscard]] constexpr bool hasPartialDerivative(const std::size_t inputIndex) const noexcept {
+            return inputIndex < inputQuantities.size() &&
+                   (partialDerivativeMask & (std::uint64_t{1} << inputIndex)) != 0;
+        }
+    };
+
+    namespace detail {
+        template <typename RelationType> struct HasRuntimeQuantityIdentifiers : std::false_type { };
+
+        template <typename Output, typename... Inputs>
+        struct HasRuntimeQuantityIdentifiers<Relation<Output, Inputs...>>
+            : std::bool_constant<
+                  RuntimeIdentifiedThermodynamicQuantity<Output> &&
+                  (RuntimeIdentifiedThermodynamicQuantity<Inputs> && ...)> { };
+
+        template <typename RelationType> struct RuntimeRelationQuantities;
+
+        template <typename Output, typename... Inputs> struct RuntimeRelationQuantities<Relation<Output, Inputs...>> {
+            using Type = std::tuple<Output, Inputs...>;
+        };
+
+        template <typename... Relations>
+        using RuntimeCatalogQuantityTuple =
+            decltype(std::tuple_cat(std::declval<typename RuntimeRelationQuantities<Relations>::Type>()...));
+
+        template <
+            typename FirstQuantity,
+            typename SecondQuantity>
+        [[nodiscard]] consteval bool runtimeQuantityIdentifiersAreCompatible() {
+            if constexpr (std::same_as<FirstQuantity, SecondQuantity>) {
+                return true;
+            } else {
+                return thermodynamicQuantityId<FirstQuantity> != thermodynamicQuantityId<SecondQuantity>;
+            }
+        }
+
+        template <
+            typename QuantityTuple,
+            std::size_t First,
+            std::size_t... Offsets>
+        [[nodiscard]] consteval bool runtimeQuantityIdentifierIsUnambiguous(std::index_sequence<Offsets...>) {
+            return (
+                runtimeQuantityIdentifiersAreCompatible<
+                    std::tuple_element_t<First, QuantityTuple>,
+                    std::tuple_element_t<First + 1 + Offsets, QuantityTuple>>() &&
+                ...
+            );
+        }
+
+        template <
+            typename QuantityTuple,
+            std::size_t... Indices>
+        [[nodiscard]] consteval bool runtimeQuantityIdentifiersAreUnambiguous(std::index_sequence<Indices...>) {
+            return (
+                runtimeQuantityIdentifierIsUnambiguous<QuantityTuple, Indices>(
+                    std::make_index_sequence<std::tuple_size_v<QuantityTuple> - Indices - 1>{}
+                ) &&
+                ...
+            );
+        }
+
+        template <bool QuantitiesAreIdentified, typename... Relations>
+        struct RuntimeRelationsAreSupported : std::false_type { };
+
+        template <typename... Relations>
+        struct RuntimeRelationsAreSupported<true, Relations...>
+            : std::bool_constant<runtimeQuantityIdentifiersAreUnambiguous<RuntimeCatalogQuantityTuple<Relations...>>(
+                  std::make_index_sequence<std::tuple_size_v<RuntimeCatalogQuantityTuple<Relations...>>>{}
+              )> { };
+
+        template <typename Catalog> struct RuntimeCatalogIsSupported : std::false_type { };
+
+        template <typename... Relations>
+        struct RuntimeCatalogIsSupported<RelationCatalog<Relations...>>
+            : RuntimeRelationsAreSupported<(HasRuntimeQuantityIdentifiers<Relations>::value && ...), Relations...> { };
+    } // namespace detail
+
+    template <typename Candidate>
+    concept RuntimeEquationOfStateModel =
+        EquationOfStateModel<Candidate> &&
+        detail::RuntimeCatalogIsSupported<typename std::remove_cvref_t<Candidate>::Relations>::value;
+
+    namespace detail {
+        template <typename EquationOfState, typename RelationType> struct RuntimeRelationStorage;
+
+        template <typename EquationOfState, typename Output, typename... Inputs>
+        struct RuntimeRelationStorage<EquationOfState, Relation<Output, Inputs...>> {
+            using RelationType = Relation<Output, Inputs...>;
+
+            static_assert(
+                sizeof...(Inputs) <= 64,
+                "Runtime EOS relation descriptors support at most 64 inputs."
+            );
+
+            inline static constexpr std::array<ThermodynamicQuantityId, sizeof...(Inputs)> inputQuantityIds{
+                thermodynamicQuantityId<Inputs>...
+            };
+
+            template <std::size_t... Indices>
+            [[nodiscard]] static consteval std::uint64_t makePartialDerivativeMask(std::index_sequence<Indices...>) {
+                using InputTuple = std::tuple<Inputs...>;
+
+                return (
+                    std::uint64_t{0} | ... |
+                    (SupportsPartialDerivative<EquationOfState, RelationType, std::tuple_element_t<Indices, InputTuple>>
+                         ? (std::uint64_t{1} << Indices)
+                         : std::uint64_t{0})
+                );
+            }
+
+            inline static constexpr std::uint64_t partialDerivativeMask =
+                makePartialDerivativeMask(std::index_sequence_for<Inputs...>{});
+
+            inline static constexpr RuntimeRelationDescriptor descriptor{
+                thermodynamicQuantityId<Output>, std::span<const ThermodynamicQuantityId>{inputQuantityIds},
+                partialDerivativeMask
+            };
+        };
+
+        template <typename EquationOfState, typename Catalog> struct RuntimeCatalogStorage;
+
+        template <typename EquationOfState, typename... Relations>
+        struct RuntimeCatalogStorage<EquationOfState, RelationCatalog<Relations...>> {
+            inline static constexpr std::array descriptors{
+                RuntimeRelationStorage<EquationOfState, Relations>::descriptor...
+            };
+        };
+
+        [[nodiscard]] inline std::expected<
+            double,
+            EvaluationError>
+        runtimeEvaluationFailure(
+            const EvaluationErrorCode code,
+            std::string message
+        ) {
+            return std::unexpected<EvaluationError>{EvaluationError{code, std::move(message)}};
+        }
+
+        template <
+            typename EquationOfState,
+            typename Output,
+            typename... Inputs>
+        [[nodiscard]] std::expected<
+            double,
+            EvaluationError>
+        evaluateRuntimeRelation(
+            const EquationOfState &equationOfState,
+            Relation<
+                Output,
+                Inputs...>,
+            const std::span<const RuntimeQuantityValue> inputValues
+        ) {
+            const auto invoke = [&]<std::size_t... Indices>(std::index_sequence<Indices...>) {
+                return eos::evaluate<Output>(equationOfState, QuantityValue<Inputs>{inputValues[Indices].value}...)
+                    .value();
+            };
+
+            try {
+                return invoke(std::index_sequence_for<Inputs...>{});
+            } catch (const EvaluationError &error) {
+                return std::unexpected<EvaluationError>{error};
+            }
+        }
+
+        template <
+            typename InputQuantity,
+            typename EquationOfState,
+            typename Output,
+            typename... Inputs>
+        [[nodiscard]] bool tryRuntimePartialDerivative(
+            const EquationOfState &equationOfState,
+            Relation<
+                Output,
+                Inputs...> relation,
+            const ThermodynamicQuantityId withRespectTo,
+            const std::span<const RuntimeQuantityValue> inputValues,
+            std::expected<
+                double,
+                EvaluationError> &result
+        ) {
+            if (withRespectTo != thermodynamicQuantityId<InputQuantity>) {
+                return false;
+            }
+
+            if constexpr (SupportsPartialDerivative<EquationOfState, Relation<Output, Inputs...>, InputQuantity>) {
+                const auto invoke = [&]<std::size_t... Indices>(std::index_sequence<Indices...>) {
+                    return eos::partialDerivative<Output, InputQuantity>(
+                               equationOfState, QuantityValue<Inputs>{inputValues[Indices].value}...
+                    )
+                        .value();
+                };
+
+                try {
+                    result = invoke(std::index_sequence_for<Inputs...>{});
+                } catch (const EvaluationError &error) {
+                    result = std::unexpected<EvaluationError>{error};
+                }
+            } else {
+                result = runtimeEvaluationFailure(
+                    EvaluationErrorCode::unsupported_derivative,
+                    "The requested EOS partial derivative is not available."
+                );
+            }
+
+            return true;
+        }
+
+        template <
+            typename EquationOfState,
+            typename Output,
+            typename... Inputs>
+        [[nodiscard]] std::expected<
+            double,
+            EvaluationError>
+        evaluateRuntimePartialDerivative(
+            const EquationOfState &equationOfState,
+            Relation<
+                Output,
+                Inputs...> relation,
+            const ThermodynamicQuantityId withRespectTo,
+            const std::span<const RuntimeQuantityValue> inputValues
+        ) {
+            std::expected<double, EvaluationError> result = runtimeEvaluationFailure(
+                EvaluationErrorCode::unsupported_derivative,
+                "The requested quantity is not an input to the EOS relation."
+            );
+
+            const bool matched =
+                (tryRuntimePartialDerivative<Inputs>(equationOfState, relation, withRespectTo, inputValues, result) ||
+                 ...);
+
+            static_cast<void>(matched);
+            return result;
+        }
+
+        template <
+            typename EquationOfState,
+            typename RelationType>
+        [[nodiscard]] bool runtimeRelationMatches(
+            const ThermodynamicQuantityId outputQuantity,
+            const std::span<const RuntimeQuantityValue> inputValues
+        ) {
+            const RuntimeRelationDescriptor &descriptor =
+                RuntimeRelationStorage<EquationOfState, RelationType>::descriptor;
+
+            if (descriptor.outputQuantity != outputQuantity ||
+                descriptor.inputQuantities.size() != inputValues.size()) {
+                return false;
+            }
+
+            for (std::size_t index = 0; index < inputValues.size(); ++index) {
+                if (descriptor.inputQuantities[index] != inputValues[index].quantity) {
+                    return false;
+                }
+            }
+
+            return true;
+        }
+
+        template <typename EquationOfState, typename Catalog> struct RuntimeCatalogDispatch;
+
+        template <typename EquationOfState, typename... Relations>
+        struct RuntimeCatalogDispatch<EquationOfState, RelationCatalog<Relations...>> {
+            [[nodiscard]] static std::expected<
+                double,
+                EvaluationError>
+            evaluate(
+                const void *object,
+                const ThermodynamicQuantityId outputQuantity,
+                const std::span<const RuntimeQuantityValue> inputValues
+            ) {
+                const auto &equationOfState                   = *static_cast<const EquationOfState *>(object);
+
+                std::expected<double, EvaluationError> result = runtimeEvaluationFailure(
+                    EvaluationErrorCode::unsupported_relation, "The requested EOS relation is not available."
+                );
+
+                const bool matched =
+                    ((runtimeRelationMatches<EquationOfState, Relations>(outputQuantity, inputValues)
+                          ? (result = evaluateRuntimeRelation(equationOfState, Relations{}, inputValues), true)
+                          : false) ||
+                     ...);
+
+                static_cast<void>(matched);
+                return result;
+            }
+
+            [[nodiscard]] static std::expected<
+                double,
+                EvaluationError>
+            partialDerivative(
+                const void *object,
+                const ThermodynamicQuantityId outputQuantity,
+                const ThermodynamicQuantityId withRespectTo,
+                const std::span<const RuntimeQuantityValue> inputValues
+            ) {
+                const auto &equationOfState                   = *static_cast<const EquationOfState *>(object);
+
+                std::expected<double, EvaluationError> result = runtimeEvaluationFailure(
+                    EvaluationErrorCode::unsupported_relation, "The requested EOS relation is not available."
+                );
+
+                const bool matched =
+                    ((runtimeRelationMatches<EquationOfState, Relations>(outputQuantity, inputValues)
+                          ? (result = evaluateRuntimePartialDerivative(
+                                 equationOfState, Relations{}, withRespectTo, inputValues
+                             ),
+                             true)
+                          : false) ||
+                     ...);
+
+                static_cast<void>(matched);
+                return result;
+            }
+        };
+
+        template <RuntimeEquationOfStateModel EquationOfState>
+        using RuntimeAdapter = RuntimeCatalogDispatch<EquationOfState, typename EquationOfState::Relations>;
+
+        template <RuntimeEquationOfStateModel EquationOfState>
+        [[nodiscard]] constexpr std::span<const RuntimeRelationDescriptor> runtimeRelationDescriptors() noexcept {
+            return RuntimeCatalogStorage<EquationOfState, typename EquationOfState::Relations>::descriptors;
+        }
+    } // namespace detail
+
+    class EquationOfStateView final {
+    public:
+        template <RuntimeEquationOfStateModel EquationOfState>
+        explicit EquationOfStateView(EquationOfState &equationOfState) noexcept
+            : m_object(std::addressof(equationOfState)),
+              m_relations(detail::runtimeRelationDescriptors<std::remove_cv_t<EquationOfState>>()),
+              m_evaluate(&detail::RuntimeAdapter<std::remove_cv_t<EquationOfState>>::evaluate),
+              m_partialDerivative(&detail::RuntimeAdapter<std::remove_cv_t<EquationOfState>>::partialDerivative) {
+        }
+
+        [[nodiscard]] std::span<const RuntimeRelationDescriptor> relations() const noexcept {
+            return m_relations;
+        }
+
+        [[nodiscard]] bool supports(
+            const ThermodynamicQuantityId outputQuantity,
+            const std::span<const ThermodynamicQuantityId> inputQuantities
+        ) const noexcept {
+            return findRelation(outputQuantity, inputQuantities) != nullptr;
+        }
+
+        template <
+            RuntimeIdentifiedThermodynamicQuantity OutputQuantity,
+            RuntimeIdentifiedThermodynamicQuantity... InputQuantities>
+        [[nodiscard]] bool supports() const noexcept {
+            constexpr std::array<ThermodynamicQuantityId, sizeof...(InputQuantities)> inputs{
+                thermodynamicQuantityId<InputQuantities>...
+            };
+
+            return supports(thermodynamicQuantityId<OutputQuantity>, std::span<const ThermodynamicQuantityId>{inputs});
+        }
+
+        [[nodiscard]] std::expected<
+            RuntimeQuantityValue,
+            EvaluationError>
+        tryEvaluate(
+            const ThermodynamicQuantityId outputQuantity,
+            const std::span<const RuntimeQuantityValue> inputValues
+        ) const {
+            const auto validation = validateRelationRequest(outputQuantity, inputValues);
+
+            if (!validation.has_value()) {
+                return std::unexpected<EvaluationError>{validation.error()};
+            }
+
+            auto result = m_evaluate(m_object, outputQuantity, inputValues);
+            if (!result.has_value()) {
+                return std::unexpected<EvaluationError>{result.error()};
+            }
+
+            return RuntimeQuantityValue{outputQuantity, *result};
+        }
+
+        template <
+            RuntimeIdentifiedThermodynamicQuantity OutputQuantity,
+            QuantityValueType... InputValues>
+        [[nodiscard]] std::expected<
+            QuantityValue<OutputQuantity>,
+            EvaluationError>
+        tryEvaluate(const InputValues... inputValues) const {
+            constexpr bool inputsHaveRuntimeIdentifiers =
+                (RuntimeIdentifiedThermodynamicQuantity<QuantityOfT<InputValues>> && ...);
+
+            static_assert(inputsHaveRuntimeIdentifiers, "Every runtime EOS input quantity needs a stable identifier.");
+
+            const std::array<RuntimeQuantityValue, sizeof...(InputValues)> runtimeInputs{
+                RuntimeQuantityValue{thermodynamicQuantityId<QuantityOfT<InputValues>>, inputValues.value()}...
+            };
+
+            auto result = tryEvaluate(
+                thermodynamicQuantityId<OutputQuantity>, std::span<const RuntimeQuantityValue>{runtimeInputs}
+            );
+
+            if (!result.has_value()) {
+                return std::unexpected<EvaluationError>{result.error()};
+            }
+
+            return QuantityValue<OutputQuantity>{result->value};
+        }
+
+        [[nodiscard]] std::expected<
+            double,
+            EvaluationError>
+        tryPartialDerivative(
+            const ThermodynamicQuantityId outputQuantity,
+            const ThermodynamicQuantityId withRespectTo,
+            const std::span<const RuntimeQuantityValue> inputValues
+        ) const {
+            const auto validation = validateRelationRequest(outputQuantity, inputValues);
+
+            if (!validation.has_value()) {
+                return std::unexpected<EvaluationError>{validation.error()};
+            }
+
+            const RuntimeRelationDescriptor &descriptor = **validation;
+            bool derivativeAvailable                    = false;
+
+            for (std::size_t index = 0; index < descriptor.inputQuantities.size(); ++index) {
+                if (descriptor.inputQuantities[index] == withRespectTo) {
+                    derivativeAvailable = descriptor.hasPartialDerivative(index);
+                    break;
+                }
+            }
+
+            if (!derivativeAvailable) {
+                return runtimeFailure<double>(
+                    EvaluationErrorCode::unsupported_derivative,
+                    "The requested EOS partial derivative is not available."
+                );
+            }
+
+            return m_partialDerivative(m_object, outputQuantity, withRespectTo, inputValues);
+        }
+
+        template <
+            RuntimeIdentifiedThermodynamicQuantity OutputQuantity,
+            RuntimeIdentifiedThermodynamicQuantity InputQuantity,
+            QuantityValueType... InputValues>
+        [[nodiscard]] std::expected<
+            PartialDerivative<
+                OutputQuantity,
+                InputQuantity>,
+            EvaluationError>
+        tryPartialDerivative(const InputValues... inputValues) const {
+            constexpr bool inputsHaveRuntimeIdentifiers =
+                (RuntimeIdentifiedThermodynamicQuantity<QuantityOfT<InputValues>> && ...);
+
+            static_assert(inputsHaveRuntimeIdentifiers, "Every runtime EOS input quantity needs a stable identifier.");
+
+            const std::array<RuntimeQuantityValue, sizeof...(InputValues)> runtimeInputs{
+                RuntimeQuantityValue{thermodynamicQuantityId<QuantityOfT<InputValues>>, inputValues.value()}...
+            };
+
+            auto result = tryPartialDerivative(
+                thermodynamicQuantityId<OutputQuantity>, thermodynamicQuantityId<InputQuantity>,
+                std::span<const RuntimeQuantityValue>{runtimeInputs}
+            );
+
+            if (!result.has_value()) {
+                return std::unexpected<EvaluationError>{result.error()};
+            }
+
+            return PartialDerivative<OutputQuantity, InputQuantity>{*result};
+        }
+
+    private:
+        using RuntimeEvaluateFunction = std::expected<
+            double,
+            EvaluationError> (*)(
+            const void *,
+            ThermodynamicQuantityId,
+            std::span<const RuntimeQuantityValue>
+        );
+
+        using RuntimePartialDerivativeFunction = std::expected<
+            double,
+            EvaluationError> (*)(
+            const void *,
+            ThermodynamicQuantityId,
+            ThermodynamicQuantityId,
+            std::span<const RuntimeQuantityValue>
+        );
+
+        [[nodiscard]] const RuntimeRelationDescriptor *findRelation(
+            const ThermodynamicQuantityId outputQuantity,
+            const std::span<const ThermodynamicQuantityId> inputQuantities
+        ) const noexcept {
+            for (const RuntimeRelationDescriptor &descriptor : m_relations) {
+                if (descriptor.outputQuantity != outputQuantity ||
+                    descriptor.inputQuantities.size() != inputQuantities.size()) {
+                    continue;
+                }
+
+                bool matches = true;
+                for (std::size_t index = 0; index < inputQuantities.size(); ++index) {
+                    if (descriptor.inputQuantities[index] != inputQuantities[index]) {
+                        matches = false;
+                        break;
+                    }
+                }
+
+                if (matches) {
+                    return std::addressof(descriptor);
+                }
+            }
+
+            return nullptr;
+        }
+
+        [[nodiscard]] std::expected<
+            const RuntimeRelationDescriptor *,
+            EvaluationError>
+        validateRelationRequest(
+            const ThermodynamicQuantityId outputQuantity,
+            const std::span<const RuntimeQuantityValue> inputValues
+        ) const {
+            bool outputAvailable     = false;
+            bool inputCountAvailable = false;
+
+            for (const RuntimeRelationDescriptor &descriptor : m_relations) {
+                if (descriptor.outputQuantity != outputQuantity) {
+                    continue;
+                }
+
+                outputAvailable = true;
+
+                if (descriptor.inputQuantities.size() != inputValues.size()) {
+                    continue;
+                }
+
+                inputCountAvailable = true;
+                bool matches        = true;
+
+                for (std::size_t index = 0; index < inputValues.size(); ++index) {
+                    if (descriptor.inputQuantities[index] != inputValues[index].quantity) {
+                        matches = false;
+                        break;
+                    }
+                }
+
+                if (matches) {
+                    return std::addressof(descriptor);
+                }
+            }
+
+            if (!outputAvailable) {
+                return runtimeFailure<const RuntimeRelationDescriptor *>(
+                    EvaluationErrorCode::unsupported_relation,
+                    "The EOS does not provide a relation for output quantity '" + std::string{outputQuantity.name()} +
+                        "'."
+                );
+            }
+
+            if (!inputCountAvailable) {
+                return runtimeFailure<const RuntimeRelationDescriptor *>(
+                    EvaluationErrorCode::wrong_input_count, "No EOS relation for output quantity '" +
+                                                                std::string{outputQuantity.name()} +
+                                                                "' accepts the supplied number of inputs."
+                );
+            }
+
+            return runtimeFailure<const RuntimeRelationDescriptor *>(
+                EvaluationErrorCode::wrong_input_quantity, "No EOS relation for output quantity '" +
+                                                               std::string{outputQuantity.name()} +
+                                                               "' accepts the supplied input quantities."
+            );
+        }
+
+        template <typename Value>
+        [[nodiscard]] static std::expected<
+            Value,
+            EvaluationError>
+        runtimeFailure(
+            const EvaluationErrorCode code,
+            std::string message
+        ) {
+            return std::unexpected<EvaluationError>{EvaluationError{code, std::move(message)}};
+        }
+
+        const void *m_object;
+        std::span<const RuntimeRelationDescriptor> m_relations;
+        RuntimeEvaluateFunction m_evaluate;
+        RuntimePartialDerivativeFunction m_partialDerivative;
+    };
+} // namespace mean_field::eos

libmeanfield/interface/field/field_mfem.cppm

@@ -1,6 +1,7 @@
 module;
 
 #include <array>
+#include <cmath>
 #include <concepts>
 #include <cstddef>
 #include <memory>
@@ -888,6 +889,282 @@ export namespace mean_field::field {
         mfem::Array<int> m_trueToReduced;
     };
 
+    /*
+     * Boundary rows expressed in a field's reduced solver ordering.
+     *
+     * This object is deliberately independent of any particular physical
+     * surface condition.  Its template constructor below combines a field,
+     * a semantic boundary, and a domain schema.  Consequently the same
+     * topology machinery can be used by any compiled surface formulation;
+     * it is not tied to enthalpy or pressure.
+     */
+    class FieldBoundaryDofMap final {
+    public:
+        FieldBoundaryDofMap() = default;
+
+        FieldBoundaryDofMap(
+            const int fieldReducedSize,
+            const mfem::Array<int> &boundaryReducedDofs
+        )
+            : m_fieldReducedSize(fieldReducedSize),
+              m_boundaryReducedDofs(boundaryReducedDofs) {
+            if (m_fieldReducedSize < 0) {
+                throw std::invalid_argument("FieldBoundaryDofMap requires a non-negative field size.");
+            }
+
+            m_boundaryReducedDofMarker.SetSize(m_fieldReducedSize);
+            m_boundaryReducedDofMarker = 0;
+
+            int previousReducedDof     = -1;
+            for (const int reducedDof : m_boundaryReducedDofs) {
+                if (reducedDof < 0 || reducedDof >= m_fieldReducedSize) {
+                    throw std::invalid_argument("FieldBoundaryDofMap contains a DOF outside the reduced field vector.");
+                }
+                if (reducedDof <= previousReducedDof) {
+                    throw std::invalid_argument("FieldBoundaryDofMap indices must be strictly increasing and unique.");
+                }
+
+                m_boundaryReducedDofMarker[reducedDof] = 1;
+                previousReducedDof                     = reducedDof;
+            }
+        }
+
+        [[nodiscard]] int field_size() const noexcept {
+            return m_fieldReducedSize;
+        }
+
+        [[nodiscard]] int size() const noexcept {
+            return m_boundaryReducedDofs.Size();
+        }
+
+        [[nodiscard]] bool empty() const noexcept {
+            return size() == 0;
+        }
+
+        [[nodiscard]] const mfem::Array<int> &reduced_dofs() const noexcept {
+            return m_boundaryReducedDofs;
+        }
+
+        [[nodiscard]] const mfem::Array<int> &reduced_dof_marker() const noexcept {
+            return m_boundaryReducedDofMarker;
+        }
+
+        [[nodiscard]] bool contains(const int reducedDof) const {
+            if (reducedDof < 0 || reducedDof >= m_fieldReducedSize) {
+                throw std::out_of_range("Reduced DOF index is outside FieldBoundaryDofMap.");
+            }
+            return m_boundaryReducedDofMarker[reducedDof] != 0;
+        }
+
+    private:
+        int m_fieldReducedSize{0};
+        mfem::Array<int> m_boundaryReducedDofs;
+        mfem::Array<int> m_boundaryReducedDofMarker;
+    };
+
+    /* Point-supported rows in a field's reduced solver ordering. */
+    class FieldPointDofMap final {
+    public:
+        FieldPointDofMap() = default;
+
+        FieldPointDofMap(
+            const int fieldReducedSize,
+            const mfem::Array<int> &pointReducedDofs
+        )
+            : m_selectedDofs(
+                  fieldReducedSize,
+                  pointReducedDofs
+              ) {
+        }
+
+        [[nodiscard]] int field_size() const noexcept {
+            return m_selectedDofs.field_size();
+        }
+
+        [[nodiscard]] int size() const noexcept {
+            return m_selectedDofs.size();
+        }
+
+        [[nodiscard]] bool empty() const noexcept {
+            return m_selectedDofs.empty();
+        }
+
+        [[nodiscard]] const mfem::Array<int> &reduced_dofs() const noexcept {
+            return m_selectedDofs.reduced_dofs();
+        }
+
+        [[nodiscard]] const mfem::Array<int> &reduced_dof_marker() const noexcept {
+            return m_selectedDofs.reduced_dof_marker();
+        }
+
+        [[nodiscard]] bool contains(const int reducedDof) const {
+            return m_selectedDofs.contains(reducedDof);
+        }
+
+    private:
+        FieldBoundaryDofMap m_selectedDofs;
+    };
+
+    template <
+        MfemDomainField FieldT,
+        utils::domain::IsBoundary BoundaryT,
+        utils::domain::IsSchema SchemaT>
+    [[nodiscard]] FieldBoundaryDofMap make_field_boundary_dof_map(
+        const mfem::ParFiniteElementSpace &finiteElementSpace,
+        const FieldDofMap &fieldDofMap
+    ) {
+        static_assert(
+            SchemaT::template contains_boundary<BoundaryT>(),
+            "The requested boundary is not registered in the supplied DomainSchema."
+        );
+
+        MFEM_VERIFY(
+            !finiteElementSpace.Nonconforming(),
+            "Field boundary true-DOF resolution currently requires a conforming mfem::ParFiniteElementSpace."
+        );
+        MFEM_VERIFY(
+            fieldDofMap.full_size() == finiteElementSpace.GetTrueVSize(),
+            "The field map and finite-element space have incompatible true-DOF sizes."
+        );
+
+        const mfem::Mesh *mesh = finiteElementSpace.GetMesh();
+        MFEM_VERIFY(mesh != nullptr, "Field boundary DOF resolution requires an MFEM mesh.");
+
+        mfem::Array<int> boundaryVDofMarker(finiteElementSpace.GetVSize());
+        boundaryVDofMarker = 0;
+
+        mfem::Array<int> boundaryElementVDofs;
+        for (int boundaryElement = 0; boundaryElement < mesh->GetNBE(); ++boundaryElement) {
+            if (!SchemaT::template boundary_attribute_matches<BoundaryT>(mesh->GetBdrAttribute(boundaryElement))) {
+                continue;
+            }
+
+            finiteElementSpace.GetBdrElementVDofs(boundaryElement, boundaryElementVDofs);
+            for (const int encodedVDof : boundaryElementVDofs) {
+                const int vdof = mfem::FiniteElementSpace::DecodeDof(encodedVDof);
+                MFEM_VERIFY(
+                    vdof >= 0 && vdof < finiteElementSpace.GetVSize(), "MFEM returned an invalid boundary vector DOF."
+                );
+                boundaryVDofMarker[vdof] = 1;
+            }
+        }
+
+        finiteElementSpace.Synchronize(boundaryVDofMarker);
+
+        mfem::Array<int> boundaryReducedDofMarker(fieldDofMap.reduced_size());
+        boundaryReducedDofMarker = 0;
+
+        for (int vdof = 0; vdof < boundaryVDofMarker.Size(); ++vdof) {
+            if (boundaryVDofMarker[vdof] == 0) {
+                continue;
+            }
+
+            const int trueDof = finiteElementSpace.GetLocalTDofNumber(vdof);
+            if (trueDof < 0) {
+                continue;
+            }
+
+            const std::optional<int> reducedDof = fieldDofMap.reduced_dof(trueDof);
+            MFEM_VERIFY(
+                reducedDof.has_value(),
+                "A boundary DOF selected for the field is absent from that field's reduced solver map."
+            );
+            boundaryReducedDofMarker[*reducedDof] = 1;
+        }
+
+        mfem::Array<int> boundaryReducedDofs;
+        mfem::FiniteElementSpace::MarkerToList(boundaryReducedDofMarker, boundaryReducedDofs);
+        return FieldBoundaryDofMap(fieldDofMap.reduced_size(), boundaryReducedDofs);
+    }
+
+    template <MfemDomainField FieldT>
+    [[nodiscard]] FieldPointDofMap make_field_point_dof_map(
+        const mfem::ParFiniteElementSpace &finiteElementSpace,
+        const FieldDofMap &fieldDofMap,
+        const mfem::Vector &point,
+        const double tolerance
+    ) {
+        MFEM_VERIFY(
+            !finiteElementSpace.Nonconforming(),
+            "Field point true-DOF resolution currently requires a conforming mfem::ParFiniteElementSpace."
+        );
+        MFEM_VERIFY(
+            fieldDofMap.full_size() == finiteElementSpace.GetTrueVSize(),
+            "The field map and finite-element space have incompatible true-DOF sizes."
+        );
+        MFEM_VERIFY(
+            std::isfinite(tolerance) && tolerance >= 0.0, "The field point tolerance must be finite and non-negative."
+        );
+
+        const mfem::Mesh *mesh = finiteElementSpace.GetMesh();
+        MFEM_VERIFY(mesh != nullptr, "Field point DOF resolution requires an MFEM mesh.");
+        MFEM_VERIFY(
+            point.Size() == mesh->SpaceDimension(), "The requested field point has the wrong coordinate dimension."
+        );
+
+        mfem::Array<int> pointVDofMarker(finiteElementSpace.GetVSize());
+        pointVDofMarker = 0;
+
+        mfem::Array<int> vertexVDofs;
+        for (int vertex = 0; vertex < mesh->GetNV(); ++vertex) {
+            const mfem::real_t *coordinates = mesh->GetVertex(vertex);
+            double distanceSquared          = 0.0;
+            for (int component = 0; component < point.Size(); ++component) {
+                const double difference = coordinates[component] - point(component);
+                distanceSquared += difference * difference;
+            }
+            if (std::sqrt(distanceSquared) > tolerance) {
+                continue;
+            }
+
+            finiteElementSpace.GetVertexVDofs(vertex, vertexVDofs);
+            for (const int encodedVDof : vertexVDofs) {
+                const int vdof = mfem::FiniteElementSpace::DecodeDof(encodedVDof);
+                MFEM_VERIFY(
+                    vdof >= 0 && vdof < finiteElementSpace.GetVSize(), "MFEM returned an invalid point vector DOF."
+                );
+                pointVDofMarker[vdof] = 1;
+            }
+        }
+
+        finiteElementSpace.Synchronize(pointVDofMarker);
+
+        mfem::Array<int> pointReducedDofMarker(fieldDofMap.reduced_size());
+        pointReducedDofMarker = 0;
+        for (int vdof = 0; vdof < pointVDofMarker.Size(); ++vdof) {
+            if (pointVDofMarker[vdof] == 0) {
+                continue;
+            }
+
+            const int trueDof = finiteElementSpace.GetLocalTDofNumber(vdof);
+            if (trueDof < 0) {
+                continue;
+            }
+
+            const std::optional<int> reducedDof = fieldDofMap.reduced_dof(trueDof);
+            MFEM_VERIFY(
+                reducedDof.has_value(),
+                "A point DOF selected for the field is absent from that field's reduced solver map."
+            );
+            pointReducedDofMarker[*reducedDof] = 1;
+        }
+
+        mfem::Array<int> pointReducedDofs;
+        mfem::FiniteElementSpace::MarkerToList(pointReducedDofMarker, pointReducedDofs);
+
+        const long long localPointDofCount = pointReducedDofs.Size();
+        long long globalPointDofCount      = 0;
+        MPI_Allreduce(
+            &localPointDofCount, &globalPointDofCount, 1, MPI_LONG_LONG, MPI_SUM, finiteElementSpace.GetComm()
+        );
+        MFEM_VERIFY(
+            globalPointDofCount == finiteElementSpace.GetVDim(),
+            "The requested geometric point must identify exactly one field vertex globally."
+        );
+
+        return FieldPointDofMap(fieldDofMap.reduced_size(), pointReducedDofs);
+    }
+
     /*
      * Canonical adapter between an MFEM GridFunction and a reduced field
      * vector.
@@ -1015,9 +1292,6 @@ export namespace mean_field::field {
     [[nodiscard]]
     FieldDofGridFunctionAdapter
     make_field_dof_grid_function_adapter(const mfem::ParFiniteElementSpace &finiteElementSpace) {
-        return FieldDofGridFunctionAdapter(
-            make_field_dof_map<FieldT, SchemaT>(finiteElementSpace),
-            finiteElementSpace
-        );
+        return FieldDofGridFunctionAdapter(make_field_dof_map<FieldT, SchemaT>(finiteElementSpace), finiteElementSpace);
     }
 } // namespace mean_field::field

libmeanfield/interface/integrators/pressure_gradient.cppm

@@ -41,7 +41,11 @@ export namespace mean_field::integrators {
         const mfem::GridFunction &compactification_coordinate,
         utils::EOS_P<EOS_T> eos
     )
-        : m_mapping(mapper, displacement, compactification_coordinate),
+        : m_mapping(
+              mapper,
+              displacement,
+              compactification_coordinate
+          ),
           m_eos(std::move(eos)) {
     }
 

libmeanfield/interface/mapping/domain_mapper.cppm

@@ -8,259 +8,288 @@ import :mapping.compactification;
 import :utils.user;
 
 export namespace mean_field::mapping {
-enum class FaceElementSide : uint8_t { element_1, element_2 };
+    enum class FaceElementSide : uint8_t { element_1, element_2 };
 
-class ElementDisplacementData {
-public:
-  ElementDisplacementData(
-      const mfem::FiniteElement &element, const mfem::Vector &displacement_dofs,
-      mfem::Ordering::Type ordering = mfem::Ordering::byNODES);
+    class ElementDisplacementData {
+    public:
+        ElementDisplacementData(
+            const mfem::FiniteElement &element,
+            const mfem::Vector &displacement_dofs,
+            mfem::Ordering::Type ordering = mfem::Ordering::byNODES
+        );
 
-  [[nodiscard]] const mfem::FiniteElement &GetElement() const noexcept;
-  [[nodiscard]] const mfem::DenseMatrix &GetDofMatrix() const noexcept;
-  [[nodiscard]] int GetDimension() const noexcept;
-  [[nodiscard]] int GetDofCount() const noexcept;
-  [[nodiscard]] mfem::Ordering::Type GetOrdering() const noexcept;
+        [[nodiscard]] const mfem::FiniteElement &GetElement() const noexcept;
+        [[nodiscard]] const mfem::DenseMatrix &GetDofMatrix() const noexcept;
+        [[nodiscard]] int GetDimension() const noexcept;
+        [[nodiscard]] int GetDofCount() const noexcept;
+        [[nodiscard]] mfem::Ordering::Type GetOrdering() const noexcept;
 
-private:
-  const mfem::FiniteElement *m_element;
-  mfem::DenseMatrix m_dof_matrix;
-  int m_dimension;
-  mfem::Ordering::Type m_ordering;
-};
+    private:
+        const mfem::FiniteElement *m_element;
+        mfem::DenseMatrix m_dof_matrix;
+        int m_dimension;
+        mfem::Ordering::Type m_ordering;
+    };
 
-struct CompactificationPointData {
-  double coordinate{0.0};
-  mfem::Vector coordinate_gradient;
-};
+    struct CompactificationPointData {
+        double coordinate{0.0};
+        mfem::Vector coordinate_gradient;
+    };
 
-[[nodiscard]] ElementDisplacementData
-ElementDisplacementDataFromElementVDofs(const mfem::FiniteElement &element,
-                                        const mfem::Vector &displacement_dofs);
+    [[nodiscard]] ElementDisplacementData ElementDisplacementDataFromElementVDofs(
+        const mfem::FiniteElement &element,
+        const mfem::Vector &displacement_dofs
+    );
 
-class ElementCompactificationData {
-public:
-  ElementCompactificationData(const mfem::FiniteElement &element,
-                              const mfem::Vector &dofs);
+    class ElementCompactificationData {
+    public:
+        ElementCompactificationData(
+            const mfem::FiniteElement &element,
+            const mfem::Vector &dofs
+        );
 
-  [[nodiscard]] const mfem::FiniteElement &GetElement() const noexcept;
-  [[nodiscard]] const mfem::Vector &GetDofs() const noexcept;
-  [[nodiscard]] int GetDofCount() const noexcept;
+        [[nodiscard]] const mfem::FiniteElement &GetElement() const noexcept;
+        [[nodiscard]] const mfem::Vector &GetDofs() const noexcept;
+        [[nodiscard]] int GetDofCount() const noexcept;
 
-private:
-  const mfem::FiniteElement *m_element;
-  mfem::Vector m_dofs;
-};
+    private:
+        const mfem::FiniteElement *m_element;
+        mfem::Vector m_dofs;
+    };
 
-struct ElementMappingData {
-  const ElementDisplacementData &displacement;
-  const ElementCompactificationData &compactification;
-};
+    struct ElementMappingData {
+        const ElementDisplacementData &displacement;
+        const ElementCompactificationData &compactification;
+    };
 
-class DomainMapper {
-public:
-  class Workspace {
-  public:
-    explicit Workspace(int dimension = 3);
+    class DomainMapper {
+    public:
+        class Workspace {
+        public:
+            explicit Workspace(int dimension = 3);
 
-    void SetDimension(int dimension);
+            void SetDimension(int dimension);
 
-    [[nodiscard]] int GetDimension() const noexcept;
+            [[nodiscard]] int GetDimension() const noexcept;
 
-  private:
-    friend class DomainMapper;
+        private:
+            friend class DomainMapper;
 
-    int m_dimension;
+            int m_dimension;
 
-    mfem::Vector m_shape;
-    mfem::DenseMatrix m_mesh_dshape;
-    mfem::Vector m_field_value;
-    mfem::DenseMatrix m_field_jacobian;
+            mfem::Vector m_shape;
+            mfem::DenseMatrix m_mesh_dshape;
+            mfem::Vector m_field_value;
+            mfem::DenseMatrix m_field_jacobian;
 
-    mfem::Vector m_compactification_shape;
-    mfem::DenseMatrix m_compactification_dshape;
-    CompactificationPointData m_compactification_point;
+            mfem::Vector m_compactification_shape;
+            mfem::DenseMatrix m_compactification_dshape;
+            CompactificationPointData m_compactification_point;
 
-    mfem::Vector m_reference_normal;
-    mfem::Vector m_mapped_normal;
-    mfem::DenseMatrix m_full_element_jacobian;
+            mfem::Vector m_reference_normal;
+            mfem::Vector m_mapped_normal;
+            mfem::DenseMatrix m_full_element_jacobian;
 
-    mfem::Vector m_vector_temp;
-    mfem::DenseMatrix m_matrix_temp_1;
-    mfem::DenseMatrix m_matrix_temp_2;
+            mfem::Vector m_vector_temp;
+            mfem::DenseMatrix m_matrix_temp_1;
+            mfem::DenseMatrix m_matrix_temp_2;
 
-    compactification::ExteriorMapResult m_exterior_result;
-    compactification::ExteriorMapVariation m_exterior_variation;
-  };
+            compactification::ExteriorMapResult m_exterior_result;
+            compactification::ExteriorMapVariation m_exterior_variation;
+        };
 
-public:
-  DomainMapper(
-      utils::DomainMapperOptions options,
-      std::unique_ptr<const compactification::ExteriorDomainMap> exterior_map);
+    public:
+        DomainMapper(
+            utils::DomainMapperOptions options,
+            std::unique_ptr<const compactification::ExteriorDomainMap> exterior_map
+        );
 
-  DomainMapper(const DomainMapper &) = delete;
-  DomainMapper &operator=(const DomainMapper &) = delete;
-  DomainMapper(DomainMapper &&) = default;
-  DomainMapper &operator=(DomainMapper &&) = default;
+        DomainMapper(const DomainMapper &)            = delete;
+        DomainMapper &operator=(const DomainMapper &) = delete;
+        DomainMapper(DomainMapper &&)                 = default;
+        DomainMapper &operator=(DomainMapper &&)      = default;
 
-  [[nodiscard]] MappingStatus
-  EvaluatePoint(const ElementMappingData &element_data,
-                mfem::ElementTransformation &transformation,
-                const mfem::IntegrationPoint &integration_point,
-                Workspace &workspace, MappingPointContext &context) const;
+        [[nodiscard]] MappingStatus EvaluatePoint(
+            const ElementMappingData &element_data,
+            mfem::ElementTransformation &transformation,
+            const mfem::IntegrationPoint &integration_point,
+            Workspace &workspace,
+            MappingPointContext &context
+        ) const;
 
-  [[nodiscard]] MappingStatus
-  EvaluateVolume(const ElementMappingData &element_data,
-                 mfem::ElementTransformation &transformation,
-                 const mfem::IntegrationPoint &integration_point,
-                 Workspace &workspace, VolumeMappingContext &context) const;
+        [[nodiscard]] MappingStatus EvaluateVolume(
+            const ElementMappingData &element_data,
+            mfem::ElementTransformation &transformation,
+            const mfem::IntegrationPoint &integration_point,
+            Workspace &workspace,
+            VolumeMappingContext &context
+        ) const;
 
-  [[nodiscard]] MappingStatus
-  EvaluateFace(const ElementMappingData &element_data,
-               mfem::FaceElementTransformations &transformation,
-               FaceElementSide side,
-               const mfem::IntegrationPoint &integration_point,
-               Workspace &workspace, FaceMappingContext &context) const;
+        [[nodiscard]] MappingStatus EvaluateFace(
+            const ElementMappingData &element_data,
+            mfem::FaceElementTransformations &transformation,
+            FaceElementSide side,
+            const mfem::IntegrationPoint &integration_point,
+            Workspace &workspace,
+            FaceMappingContext &context
+        ) const;
 
-  [[nodiscard]] MappingStatus
-  EvaluatePointVariation(const ElementMappingData &element_data,
-                         const ElementDisplacementData &direction,
-                         mfem::ElementTransformation &transformation,
-                         const mfem::IntegrationPoint &integration_point,
-                         const MappingPointContext &base_context,
-                         Workspace &workspace,
-                         MappingPointVariation &variation) const;
+        [[nodiscard]] MappingStatus EvaluatePointVariation(
+            const ElementMappingData &element_data,
+            const ElementDisplacementData &direction,
+            mfem::ElementTransformation &transformation,
+            const mfem::IntegrationPoint &integration_point,
+            const MappingPointContext &base_context,
+            Workspace &workspace,
+            MappingPointVariation &variation
+        ) const;
 
-  [[nodiscard]] MappingStatus
-  EvaluateVolumeVariation(const ElementMappingData &element_data,
-                          const ElementDisplacementData &direction,
-                          mfem::ElementTransformation &transformation,
-                          const mfem::IntegrationPoint &integration_point,
-                          const VolumeMappingContext &base_context,
-                          Workspace &workspace,
-                          VolumeMappingVariation &variation) const;
+        [[nodiscard]] MappingStatus EvaluateVolumeVariation(
+            const ElementMappingData &element_data,
+            const ElementDisplacementData &direction,
+            mfem::ElementTransformation &transformation,
+            const mfem::IntegrationPoint &integration_point,
+            const VolumeMappingContext &base_context,
+            Workspace &workspace,
+            VolumeMappingVariation &variation
+        ) const;
 
-  [[nodiscard]] MappingStatus EvaluateFaceVariation(
-      const ElementMappingData &element_data,
-      const ElementDisplacementData &direction,
-      mfem::FaceElementTransformations &transformation, FaceElementSide side,
-      const mfem::IntegrationPoint &integration_point,
-      const FaceMappingContext &base_context, Workspace &workspace,
-      FaceMappingVariation &variation) const;
+        [[nodiscard]] MappingStatus EvaluateFaceVariation(
+            const ElementMappingData &element_data,
+            const ElementDisplacementData &direction,
+            mfem::FaceElementTransformations &transformation,
+            FaceElementSide side,
+            const mfem::IntegrationPoint &integration_point,
+            const FaceMappingContext &base_context,
+            Workspace &workspace,
+            FaceMappingVariation &variation
+        ) const;
 
-  [[nodiscard]] bool IsCompactifiedElement(
-      const mfem::ElementTransformation &transformation) const noexcept;
-  [[nodiscard]] int GetDimension() const noexcept;
-  [[nodiscard]] const compactification::ExteriorDomainMap &
-  GetExteriorMap() const noexcept;
+        [[nodiscard]] bool IsCompactifiedElement(const mfem::ElementTransformation &transformation) const noexcept;
+        [[nodiscard]] int GetDimension() const noexcept;
+        [[nodiscard]] const compactification::ExteriorDomainMap &GetExteriorMap() const noexcept;
 
-private:
-  void ValidateElementData(const ElementMappingData &element_data) const;
+    private:
+        void ValidateElementData(const ElementMappingData &element_data) const;
 
-  void EvaluateField(const ElementDisplacementData &field,
-                     mfem::ElementTransformation &transformation,
-                     const mfem::IntegrationPoint &integration_point,
-                     Workspace &workspace, mfem::Vector &value,
-                     mfem::DenseMatrix &jacobian) const;
+        void EvaluateField(
+            const ElementDisplacementData &field,
+            mfem::ElementTransformation &transformation,
+            const mfem::IntegrationPoint &integration_point,
+            Workspace &workspace,
+            mfem::Vector &value,
+            mfem::DenseMatrix &jacobian
+        ) const;
 
-  [[nodiscard]] MappingStatus EvaluateCompactificationCoordinate(
-      const ElementCompactificationData &compactification,
-      mfem::ElementTransformation &transformation,
-      const mfem::IntegrationPoint &integration_point, Workspace &workspace,
-      CompactificationPointData &point_data) const;
+        [[nodiscard]] MappingStatus EvaluateCompactificationCoordinate(
+            const ElementCompactificationData &compactification,
+            mfem::ElementTransformation &transformation,
+            const mfem::IntegrationPoint &integration_point,
+            Workspace &workspace,
+            CompactificationPointData &point_data
+        ) const;
 
-  [[nodiscard]] static mfem::ElementTransformation &
-  SelectFaceElementTransformation(
-      mfem::FaceElementTransformations &transformation, FaceElementSide side);
+        [[nodiscard]] static mfem::ElementTransformation &SelectFaceElementTransformation(
+            mfem::FaceElementTransformations &transformation,
+            FaceElementSide side
+        );
 
-  [[nodiscard]] static const mfem::IntegrationPoint &
-  SelectFaceElementIntegrationPoint(
-      mfem::FaceElementTransformations &transformation, FaceElementSide side);
+        [[nodiscard]] static const mfem::IntegrationPoint &SelectFaceElementIntegrationPoint(
+            mfem::FaceElementTransformations &transformation,
+            FaceElementSide side
+        );
 
-  utils::DomainMapperOptions m_options;
-  std::unique_ptr<const compactification::ExteriorDomainMap> m_exterior_map;
-};
+        utils::DomainMapperOptions m_options;
+        std::unique_ptr<const compactification::ExteriorDomainMap> m_exterior_map;
+    };
 
-class GridFunctionMappingEvaluator {
-public:
-  /*
-   * The evaluator references the supplied grid functions and caches copies of
-   * their element-local DOFs. Call InvalidateCache() or Refresh() after either
-   * grid function's values are modified. Finite-element-space sequence changes
-   * are detected automatically.
-   *
-   * This object owns mutable workspace and cache state and is not thread-safe.
-   */
-  GridFunctionMappingEvaluator(
-      const DomainMapper &mapper,
-      const mfem::GridFunction &displacement,
-      const mfem::GridFunction &compactification_coordinate);
+    class GridFunctionMappingEvaluator {
+    public:
+        /*
+         * The evaluator references the supplied grid functions and caches copies of
+         * their element-local DOFs. Call InvalidateCache() or Refresh() after either
+         * grid function's values are modified. Finite-element-space sequence changes
+         * are detected automatically.
+         *
+         * This object owns mutable workspace and cache state and is not thread-safe.
+         */
+        GridFunctionMappingEvaluator(
+            const DomainMapper &mapper,
+            const mfem::GridFunction &displacement,
+            const mfem::GridFunction &compactification_coordinate
+        );
 
-  /*
-   * Discard all element-local field data. The next evaluation reloads its
-   * requested element lazily. This operation is idempotent.
-   */
-  void InvalidateCache() noexcept;
+        /*
+         * Discard all element-local field data. The next evaluation reloads its
+         * requested element lazily. This operation is idempotent.
+         */
+        void InvalidateCache() noexcept;
 
-  /*
-   * Reload the currently cached element immediately. If no element has been
-   * evaluated yet, Refresh() is a validated no-op. If either finite-element
-   * space changed sequence, the old element ID is discarded and the next
-   * evaluation reloads lazily against the updated spaces.
-   */
-  void Refresh();
+        /*
+         * Reload the currently cached element immediately. If no element has been
+         * evaluated yet, Refresh() is a validated no-op. If either finite-element
+         * space changed sequence, the old element ID is discarded and the next
+         * evaluation reloads lazily against the updated spaces.
+         */
+        void Refresh();
 
-  [[nodiscard]] MappingStatus
-  EvaluatePoint(mfem::ElementTransformation &transformation,
-                const mfem::IntegrationPoint &integration_point,
-                MappingPointContext &context);
+        [[nodiscard]] MappingStatus EvaluatePoint(
+            mfem::ElementTransformation &transformation,
+            const mfem::IntegrationPoint &integration_point,
+            MappingPointContext &context
+        );
 
-  [[nodiscard]] MappingStatus
-  EvaluateVolume(mfem::ElementTransformation &transformation,
-                 const mfem::IntegrationPoint &integration_point,
-                 VolumeMappingContext &context);
+        [[nodiscard]] MappingStatus EvaluateVolume(
+            mfem::ElementTransformation &transformation,
+            const mfem::IntegrationPoint &integration_point,
+            VolumeMappingContext &context
+        );
 
-  [[nodiscard]] MappingStatus
-  EvaluateFace(mfem::FaceElementTransformations &transformation,
-               FaceElementSide side,
-               const mfem::IntegrationPoint &integration_point,
-               FaceMappingContext &context);
+        [[nodiscard]] MappingStatus EvaluateFace(
+            mfem::FaceElementTransformations &transformation,
+            FaceElementSide side,
+            const mfem::IntegrationPoint &integration_point,
+            FaceMappingContext &context
+        );
 
-  [[nodiscard]] VolumeQuadratureContext
-  GetQuadratureContext(mfem::ElementTransformation &transformation,
-                       const mfem::IntegrationPoint &integration_point);
+        [[nodiscard]] VolumeQuadratureContext GetQuadratureContext(
+            mfem::ElementTransformation &transformation,
+            const mfem::IntegrationPoint &integration_point
+        );
 
-  [[nodiscard]] FaceQuadratureContext
-  GetFaceQuadratureContext(
-      mfem::FaceElementTransformations &transformation,
-      const mfem::IntegrationPoint &integration_point,
-      FaceElementSide side = FaceElementSide::element_1);
+        [[nodiscard]] FaceQuadratureContext GetFaceQuadratureContext(
+            mfem::FaceElementTransformations &transformation,
+            const mfem::IntegrationPoint &integration_point,
+            FaceElementSide side = FaceElementSide::element_1
+        );
 
-  void GetPhysicalPoint(mfem::ElementTransformation &transformation,
-                        const mfem::IntegrationPoint &integration_point,
-                        mfem::Vector &physical_position);
+        void GetPhysicalPoint(
+            mfem::ElementTransformation &transformation,
+            const mfem::IntegrationPoint &integration_point,
+            mfem::Vector &physical_position
+        );
 
-private:
-  void ValidateFieldBindings() const;
-  [[nodiscard]] bool InvalidateForChangedSpaces();
-  void LoadElement(int element_id);
+    private:
+        void ValidateFieldBindings() const;
+        [[nodiscard]] bool InvalidateForChangedSpaces();
+        void LoadElement(int element_id);
 
-  const DomainMapper &m_mapper;
-  const mfem::GridFunction &m_displacement;
-  const mfem::GridFunction &m_compactification_coordinate;
-  const mfem::FiniteElementSpace *m_displacement_space;
-  const mfem::FiniteElementSpace *m_compactification_space;
-  long m_displacement_space_sequence;
-  long m_compactification_space_sequence;
-  DomainMapper::Workspace m_workspace;
+        const DomainMapper &m_mapper;
+        const mfem::GridFunction &m_displacement;
+        const mfem::GridFunction &m_compactification_coordinate;
+        const mfem::FiniteElementSpace *m_displacement_space;
+        const mfem::FiniteElementSpace *m_compactification_space;
+        long m_displacement_space_sequence;
+        long m_compactification_space_sequence;
+        DomainMapper::Workspace m_workspace;
 
-  mfem::Array<int> m_displacement_dofs;
-  mfem::Array<int> m_compactification_dofs;
-  mfem::Vector m_element_displacement;
-  mfem::Vector m_element_compactification;
-  std::unique_ptr<ElementDisplacementData> m_displacement_data;
-  std::unique_ptr<ElementCompactificationData> m_compactification_data;
-  int m_cached_element_id{-1};
-};
+        mfem::Array<int> m_displacement_dofs;
+        mfem::Array<int> m_compactification_dofs;
+        mfem::Vector m_element_displacement;
+        mfem::Vector m_element_compactification;
+        std::unique_ptr<ElementDisplacementData> m_displacement_data;
+        std::unique_ptr<ElementCompactificationData> m_compactification_data;
+        int m_cached_element_id{-1};
+    };
 
 } // namespace mean_field::mapping

libmeanfield/interface/mean_field.cppm

@@ -54,10 +54,19 @@ export import :operators.prepared_displacement_residual;
 export import :model.structure_profile;
 export import :model.structure.base;
 export import :model.structure.polytropic;
-export import :eos.base;
+export import :eos.quantities;
+export import :eos.relations;
+export import :eos.concepts;
+export import :eos.evaluation;
+export import :eos.pressure_surface;
+export import :eos.runtime;
 export import :eos.polytrope;
-export import :surface.base;
-export import :surface.isobaric;
+export import :surface.constant;
+export import :surface.dependencies;
+export import :surface.compiled;
+export import :surface.compiler;
 export import :model.stellar;
 export import :operators.prepared_mass_normalization;
+export import :operators.prepared_centering_constraint;
+export import :operators.prepared_surface_constraint;
 export import :operators.prepared_stellar_equilibrium;

libmeanfield/interface/models/stellar_model.cppm

@@ -7,62 +7,84 @@ module;
 
 export module mean_field:model.stellar;
 
-export import :eos.base;
+export import :eos.runtime;
 export import :model.structure.base;
-export import :surface.base;
+export import :surface.compiler;
 
 export namespace mean_field::models {
-    template <typename Candidate>
-    concept StructurePrescription =
-        std::derived_from<std::remove_cvref_t<Candidate>, mean_field::models::structure::StructureBase>;
+    namespace detail {
+        template <typename Candidate>
+        concept ConstEquationOfStateReference =
+            std::is_lvalue_reference_v<Candidate> && std::is_const_v<std::remove_reference_t<Candidate>> &&
+            eos::EquationOfStateModel<std::remove_cvref_t<Candidate>>;
+    } // namespace detail
 
     template <typename Candidate>
-    concept SurfacePrescription = std::derived_from<std::remove_cvref_t<Candidate>, mean_field::surface::SurfaceBase>;
+    concept StructurePrescription = requires(
+        const std::remove_cvref_t<Candidate> &structurePrescription,
+        const structure::StructureSeedRequest &seedRequest
+    ) {
+        { structurePrescription.equationOfState() } noexcept -> detail::ConstEquationOfStateReference;
+        { structurePrescription.targetMass() } noexcept -> std::same_as<double>;
+        { structurePrescription.makeInitialSeed(seedRequest) } -> std::same_as<structure::StructureSeed>;
+        { structurePrescription.validate() } -> std::same_as<void>;
+    };
 
-    /*
-     * Public ownership facade for a physical structure prescription and its
-     * stellar-surface prescription.
-     *
-     * The concrete prescriptions are allocated once at construction. Their
-     * stable addresses allow future prepared operators and contexts to borrow
-     * references without making ownership part of the user-facing API.
-     */
+    template <StructurePrescription Candidate>
+    using StructureEquationOfStateT =
+        std::remove_cvref_t<decltype(std::declval<const std::remove_cvref_t<Candidate> &>().equationOfState())>;
+
+    template <typename Candidate, typename EquationOfState>
+    concept SurfacePrescription =
+        surface::ConstantPressureSurfaceType<Candidate> &&
+        surface::PressureSurfaceCompilable<surface::BarotropicSurfaceFormulation, std::remove_cvref_t<EquationOfState>>;
+
+    template <StructurePrescription Structure>
+        requires SurfacePrescription<surface::ConstantPressureSurface, StructureEquationOfStateT<Structure>>
     class StellarModel final {
     public:
-        template <
-            StructurePrescription StructureType,
-            SurfacePrescription SurfaceType>
+        using StructurePrescriptionType = Structure;
+        using SurfacePrescriptionType   = surface::ConstantPressureSurface;
+        using EquationOfStateType       = StructureEquationOfStateT<Structure>;
+        using SurfaceConstraintType =
+            surface::CompiledPressureSurfaceConstraintT<surface::BarotropicSurfaceFormulation, EquationOfStateType>;
+
+        template <typename StructureArgument>
+            requires std::same_as<
+                         std::remove_cvref_t<StructureArgument>,
+                         Structure>
         explicit StellarModel(
-            StructureType &&structurePrescription,
-            SurfaceType &&surfacePrescription
+            StructureArgument &&structurePrescription,
+            const surface::ConstantPressureSurface surfacePrescription
         )
-            : StellarModel(
-                  std::make_unique<std::remove_cvref_t<StructureType>>(
-                      std::forward<StructureType>(structurePrescription)
-                  ),
-                  std::make_unique<std::remove_cvref_t<SurfaceType>>(std::forward<SurfaceType>(surfacePrescription))
+            : m_structurePrescription(
+                  std::make_unique<Structure>(std::forward<StructureArgument>(structurePrescription))
+              ),
+              m_surfacePrescription(std::make_unique<surface::ConstantPressureSurface>(surfacePrescription)),
+              m_compiledSurfaceConstraint(
+                  std::make_unique<SurfaceConstraintType>(validateAndCompileSurface(
+                      *m_structurePrescription,
+                      *m_surfacePrescription
+                  ))
               ) {
         }
 
         ~StellarModel()                                   = default;
 
         StellarModel(const StellarModel &)                = delete;
-
         StellarModel &operator=(const StellarModel &)     = delete;
-
         StellarModel(StellarModel &&) noexcept            = default;
-
         StellarModel &operator=(StellarModel &&) noexcept = default;
 
-        [[nodiscard]] const mean_field::models::structure::StructureBase &structurePrescription() const noexcept {
+        [[nodiscard]] const Structure &structurePrescription() const noexcept {
             return *m_structurePrescription;
         }
 
-        [[nodiscard]] const mean_field::surface::SurfaceBase &surfacePrescription() const noexcept {
+        [[nodiscard]] const surface::ConstantPressureSurface &surfacePrescription() const noexcept {
             return *m_surfacePrescription;
         }
 
-        [[nodiscard]] const mean_field::eos::EquationOfState &equationOfState() const noexcept {
+        [[nodiscard]] const EquationOfStateType &equationOfState() const noexcept {
             return m_structurePrescription->equationOfState();
         }
 
@@ -70,45 +92,99 @@ export namespace mean_field::models {
             return m_structurePrescription->targetMass();
         }
 
-        [[nodiscard]] mean_field::models::structure::StructureSeed
-        makeInitialSeed(const mean_field::models::structure::StructureSeedRequest &request) const {
+        [[nodiscard]] structure::StructureSeed makeInitialSeed(const structure::StructureSeedRequest &request) const {
             return m_structurePrescription->makeInitialSeed(request);
         }
 
-        [[nodiscard]] const mean_field::surface::ResolvedSurfaceCondition &resolvedSurfaceCondition() const noexcept {
-            return m_resolvedSurfaceCondition;
+        [[nodiscard]] const SurfaceConstraintType &compiledSurfaceConstraint() const noexcept {
+            return *m_compiledSurfaceConstraint;
         }
 
     private:
-        explicit StellarModel(
-            std::unique_ptr<mean_field::models::structure::StructureBase> structurePrescription,
-            std::unique_ptr<mean_field::surface::SurfaceBase> surfacePrescription
-        )
-            : m_structurePrescription(std::move(structurePrescription)),
-              m_surfacePrescription(std::move(surfacePrescription)),
-              m_resolvedSurfaceCondition(validateAndResolve(
-                  *m_structurePrescription,
-                  *m_surfacePrescription
-              )) {
-        }
-
-        [[nodiscard]] static mean_field::surface::ResolvedSurfaceCondition validateAndResolve(
-            const mean_field::models::structure::StructureBase &structurePrescription,
-            const mean_field::surface::SurfaceBase &surfacePrescription
+        [[nodiscard]] static SurfaceConstraintType validateAndCompileSurface(
+            const Structure &structurePrescription,
+            const surface::ConstantPressureSurface &surfacePrescription
         ) {
             structurePrescription.validate();
 
-            const mean_field::eos::EquationOfState &equationOfState = structurePrescription.equationOfState();
-
-            surfacePrescription.validate(equationOfState);
-
-            return surfacePrescription.resolve(equationOfState);
+            return surface::compilePressureSurfaceConstraint<surface::BarotropicSurfaceFormulation>(
+                surfacePrescription, structurePrescription.equationOfState()
+            );
         }
 
-        std::unique_ptr<mean_field::models::structure::StructureBase> m_structurePrescription;
+        std::unique_ptr<Structure> m_structurePrescription;
+        std::unique_ptr<surface::ConstantPressureSurface> m_surfacePrescription;
+        std::unique_ptr<SurfaceConstraintType> m_compiledSurfaceConstraint;
+    };
 
-        std::unique_ptr<mean_field::surface::SurfaceBase> m_surfacePrescription;
+    template <typename Structure>
+    StellarModel(
+        Structure &&,
+        surface::ConstantPressureSurface
+    ) -> StellarModel<std::remove_cvref_t<Structure>>;
 
-        mean_field::surface::ResolvedSurfaceCondition m_resolvedSurfaceCondition;
+    namespace detail {
+        template <typename Candidate> struct IsStellarModel : std::false_type { };
+
+        template <typename Structure> struct IsStellarModel<StellarModel<Structure>> : std::true_type { };
+    } // namespace detail
+
+    template <typename Candidate>
+    concept StellarModelType = detail::IsStellarModel<std::remove_cvref_t<Candidate>>::value;
+
+    class StellarModelView final {
+    public:
+        template <typename Model>
+            requires StellarModelType<Model> &&
+                         eos::RuntimeEquationOfStateModel<typename std::remove_cvref_t<Model>::EquationOfStateType>
+        explicit StellarModelView(Model &model) noexcept
+            : m_equationOfState(model.equationOfState()),
+              m_structurePrescription(std::addressof(model.structurePrescription())),
+              m_makeInitialSeed(&makeInitialSeedFor<typename std::remove_cvref_t<Model>::StructurePrescriptionType>),
+              m_targetMass(model.targetMass()),
+              m_surfaceCondition(model.compiledSurfaceConstraint().descriptor()),
+              m_surfaceDependencies(model.compiledSurfaceConstraint().runtimeDependencies()) {
+        }
+
+        [[nodiscard]] eos::EquationOfStateView equationOfState() const noexcept {
+            return m_equationOfState;
+        }
+
+        [[nodiscard]] double targetMass() const noexcept {
+            return m_targetMass;
+        }
+
+        [[nodiscard]] structure::StructureSeed makeInitialSeed(const structure::StructureSeedRequest &request) const {
+            return m_makeInitialSeed(m_structurePrescription, request);
+        }
+
+        [[nodiscard]] surface::PressureSurfaceDescriptor surfaceCondition() const noexcept {
+            return m_surfaceCondition;
+        }
+
+        [[nodiscard]] surface::RuntimeSurfaceConstraintDependencies surfaceDependencies() const noexcept {
+            return m_surfaceDependencies;
+        }
+
+    private:
+        using MakeInitialSeedFunction = structure::StructureSeed (*)(
+            const void *,
+            const structure::StructureSeedRequest &
+        );
+
+        template <StructurePrescription Structure>
+        [[nodiscard]] static structure::StructureSeed makeInitialSeedFor(
+            const void *structurePrescription,
+            const structure::StructureSeedRequest &request
+        ) {
+            return static_cast<const Structure *>(structurePrescription)->makeInitialSeed(request);
+        }
+
+        eos::EquationOfStateView m_equationOfState;
+        const void *m_structurePrescription;
+        MakeInitialSeedFunction m_makeInitialSeed;
+        double m_targetMass;
+        surface::PressureSurfaceDescriptor m_surfaceCondition;
+        surface::RuntimeSurfaceConstraintDependencies m_surfaceDependencies;
     };
 } // namespace mean_field::models

libmeanfield/interface/models/structure/polytropic.cppm

@@ -12,20 +12,20 @@ export import :model.structure.base;
 import :utils.misc;
 
 export namespace mean_field::models::structure {
-    class PolytropicStructure final : public StructureBase {
+    class PolytropicStructure final {
     public:
         explicit PolytropicStructure(
             eos::Polytrope equationOfState,
             double targetMass
         );
 
-        [[nodiscard]] const eos::EquationOfState &equationOfState() const noexcept override;
+        [[nodiscard]] const eos::Polytrope &equationOfState() const noexcept;
 
-        [[nodiscard]] double targetMass() const noexcept override;
+        [[nodiscard]] double targetMass() const noexcept;
 
-        [[nodiscard]] StructureSeed makeInitialSeed(const StructureSeedRequest &request) const override;
+        [[nodiscard]] StructureSeed makeInitialSeed(const StructureSeedRequest &request) const;
 
-        void validate() const override;
+        void validate() const;
 
     private:
         struct LaneEmdenPoint {

libmeanfield/interface/models/structure/structure_base.cppm

@@ -1,7 +1,7 @@
 module;
 #include <mfem.hpp>
 export module mean_field:model.structure.base;
-export import :eos.base;
+export import :eos.runtime;
 
 export namespace mean_field::models::structure {
     struct StructureSeed {
@@ -23,7 +23,7 @@ export namespace mean_field::models::structure {
     public:
         virtual ~StructureBase()                                                                       = default;
 
-        [[nodiscard]] virtual const eos::EquationOfState &equationOfState() const noexcept             = 0;
+        [[nodiscard]] virtual eos::EquationOfStateView equationOfState() const noexcept                = 0;
 
         [[nodiscard]] virtual double targetMass() const noexcept                                       = 0;
 

libmeanfield/interface/operators/prepared_centering_constraint.cppm

@@ -0,0 +1,103 @@
+module;
+
+#include <cmath>
+#include <utility>
+
+#include <mfem.hpp>
+
+export module mean_field:operators.prepared_centering_constraint;
+
+export import :field.mfem;
+
+export namespace mean_field::operators {
+    struct PreparedCenteringConstraintReport final {
+        bool cachedCenterDisplacement{false};
+
+        [[nodiscard]] bool DidAnyWork() const noexcept {
+            return cachedCenterDisplacement;
+        }
+    };
+
+    /*
+     * Strong translational gauge: the material point at the computational
+     * origin has zero displacement. The three corresponding displacement
+     * residual rows replace redundant force-balance rows.
+     */
+    class PreparedCenteringConstraint final {
+    public:
+        explicit PreparedCenteringConstraint(field::FieldPointDofMap centerRows)
+            : m_centerRows(std::move(centerRows)),
+              m_centerDisplacement(m_centerRows.size()) {
+        }
+
+        [[nodiscard]] PreparedCenteringConstraintReport Prepare(
+            const mfem::Vector &displacement,
+            const bool displacementChanged
+        ) {
+            MFEM_VERIFY(
+                displacement.Size() == m_centerRows.field_size(),
+                "The centering constraint received a displacement vector with the wrong size."
+            );
+
+            PreparedCenteringConstraintReport report;
+            if (!m_isPrepared || displacementChanged) {
+                for (int centerIndex = 0; centerIndex < m_centerRows.size(); ++centerIndex) {
+                    const double value = displacement(m_centerRows.reduced_dofs()[centerIndex]);
+                    MFEM_VERIFY(
+                        std::isfinite(value), "The centering constraint received a non-finite center displacement."
+                    );
+                    m_centerDisplacement(centerIndex) = value;
+                }
+                report.cachedCenterDisplacement = true;
+            }
+
+            m_isPrepared = true;
+            return report;
+        }
+
+        void ApplyResidualRows(mfem::Vector &displacementResidual) const {
+            VerifyPrepared();
+            MFEM_VERIFY(
+                displacementResidual.Size() == m_centerRows.field_size(),
+                "The centering constraint received a displacement residual with the wrong size."
+            );
+
+            for (int centerIndex = 0; centerIndex < m_centerRows.size(); ++centerIndex) {
+                displacementResidual(m_centerRows.reduced_dofs()[centerIndex]) = m_centerDisplacement(centerIndex);
+            }
+        }
+
+        void ApplyJacobianRows(
+            const mfem::Vector &displacementVariation,
+            mfem::Vector &displacementAction
+        ) const {
+            VerifyPrepared();
+            MFEM_VERIFY(
+                displacementVariation.Size() == m_centerRows.field_size() &&
+                    displacementAction.Size() == m_centerRows.field_size(),
+                "The centering constraint received a Jacobian vector with the wrong size."
+            );
+
+            for (const int centerRow : m_centerRows.reduced_dofs()) {
+                displacementAction(centerRow) = displacementVariation(centerRow);
+            }
+        }
+
+        [[nodiscard]] bool IsPrepared() const noexcept {
+            return m_isPrepared;
+        }
+
+        [[nodiscard]] const field::FieldPointDofMap &GetCenterRows() const noexcept {
+            return m_centerRows;
+        }
+
+    private:
+        void VerifyPrepared() const {
+            MFEM_VERIFY(m_isPrepared, "The centering constraint must be prepared before row application.");
+        }
+
+        field::FieldPointDofMap m_centerRows;
+        mfem::Vector m_centerDisplacement;
+        bool m_isPrepared{false};
+    };
+} // namespace mean_field::operators

libmeanfield/interface/operators/prepared_stellar_equilibrium.cppm

@@ -1,7 +1,9 @@
 module;
 
 #include <compare>
+#include <concepts>
 #include <cstdint>
+#include <type_traits>
 
 #include <mfem.hpp>
 
@@ -16,9 +18,11 @@ export import :operators.context.gravity_field;
 export import :operators.gravity_field;
 export import :operators.gravity_field_jacobian;
 export import :operators.prepared_barotropic_closure;
+export import :operators.prepared_centering_constraint;
 export import :operators.prepared_displacement_residual;
 export import :operators.prepared_hydrostatic_equilibrium;
 export import :operators.prepared_mass_normalization;
+export import :operators.prepared_surface_constraint;
 export import :physics.rigid_rotation;
 export import :utils.blocks;
 
@@ -50,11 +54,14 @@ export namespace mean_field::operators {
         PreparedHydrostaticEquilibriumReport hydrostatic;
         PreparedDisplacementResidualReport displacement;
         PreparedMassNormalizationReport massNormalization;
+        PreparedSurfaceConstraintReport surfaceConstraint;
+        PreparedCenteringConstraintReport centeringConstraint;
         bool assembledResidual{false};
 
         [[nodiscard]] bool DidAnyChildWork() const noexcept {
             return gravity.DidAnyWork() || barotropicClosure.DidAnyWork() || hydrostatic.DidAnyWork() ||
-                   displacement.DidAnyWork() || massNormalization.DidAnyWork();
+                   displacement.DidAnyWork() || massNormalization.DidAnyWork() || surfaceConstraint.DidAnyWork() ||
+                   centeringConstraint.DidAnyWork();
         }
 
         [[nodiscard]] bool DidAnyWork() const noexcept {
@@ -74,19 +81,27 @@ export namespace mean_field::operators {
 
     class PreparedStellarEquilibriumOperator final : public mfem::Operator {
     public:
+        template <models::StellarModelType Model>
+            requires std::same_as<
+                         typename std::remove_cvref_t<Model>::EquationOfStateType,
+                         eos::Polytrope> &&
+                     SingleFieldPressureSurfaceConstraintFor<
+                         typename std::remove_cvref_t<Model>::SurfaceConstraintType,
+                         field::Enthalpy> &&
+                     std::is_lvalue_reference_v<Model &&>
         PreparedStellarEquilibriumOperator(
             fem::FEM &f,
             const mapping::DomainMapper &domainMapper,
-            const eos::Polytrope &equationOfState,
-            double targetMass
-        );
-
-        PreparedStellarEquilibriumOperator(
-            fem::FEM &f,
-            const mapping::DomainMapper &domainMapper,
-            const eos::Polytrope &equationOfState,
-            const models::StellarModel &stellarModel
-        );
+            Model &&stellarModel
+        )
+            : PreparedStellarEquilibriumOperator(
+                  f,
+                  domainMapper,
+                  stellarModel.equationOfState(),
+                  stellarModel.targetMass(),
+                  PressureSurfaceConstraintView{stellarModel.compiledSurfaceConstraint()}
+              ) {
+        }
 
         PreparedStellarEquilibriumOperator(const PreparedStellarEquilibriumOperator &)            = delete;
         PreparedStellarEquilibriumOperator &operator=(const PreparedStellarEquilibriumOperator &) = delete;
@@ -122,6 +137,8 @@ export namespace mean_field::operators {
         [[nodiscard]] const PreparedHydrostaticEquilibriumOperator &GetHydrostaticOperator() const noexcept;
         [[nodiscard]] const PreparedDisplacementResidualOperator &GetDisplacementOperator() const noexcept;
         [[nodiscard]] const PreparedMassNormalizationOperator &GetMassNormalizationOperator() const noexcept;
+        [[nodiscard]] const PreparedPressureSurfaceConstraint &GetSurfaceConstraintOperator() const noexcept;
+        [[nodiscard]] const PreparedCenteringConstraint &GetCenteringConstraintOperator() const noexcept;
 
     private:
         struct ConstructionData;
@@ -133,6 +150,15 @@ export namespace mean_field::operators {
             const mapping::DomainMapper &domainMapper,
             const eos::Polytrope &equationOfState,
             double targetMass,
+            PressureSurfaceConstraintView surfaceConstraint
+        );
+
+        PreparedStellarEquilibriumOperator(
+            fem::FEM &f,
+            const mapping::DomainMapper &domainMapper,
+            const eos::Polytrope &equationOfState,
+            double targetMass,
+            PressureSurfaceConstraintView surfaceConstraint,
             ConstructionData constructionData
         );
 
@@ -150,6 +176,8 @@ export namespace mean_field::operators {
         PreparedHydrostaticEquilibriumOperator m_hydrostaticOperator;
         PreparedDisplacementResidualOperator m_displacementOperator;
         PreparedMassNormalizationOperator m_massNormalizationOperator;
+        PreparedPressureSurfaceConstraint m_surfaceConstraintOperator;
+        PreparedCenteringConstraint m_centeringConstraintOperator;
 
         StellarEquilibriumDependencies m_preparedDependencies;
         mfem::Vector m_cachedResidual;

libmeanfield/interface/operators/prepared_surface_constraint.cppm

@@ -0,0 +1,235 @@
+module;
+
+#include <cmath>
+#include <concepts>
+#include <memory>
+#include <type_traits>
+#include <utility>
+
+#include <mfem.hpp>
+
+export module mean_field:operators.prepared_surface_constraint;
+
+export import :field.mfem;
+export import :surface.compiled;
+
+namespace mean_field::operators::detail {
+    template <eos::ThermodynamicQuantityType Quantity> struct SingleQuantitySurfaceState final {
+        eos::QuantityValue<Quantity> quantityValue;
+
+        [[nodiscard]] eos::QuantityValue<Quantity> value(Quantity) const noexcept {
+            return quantityValue;
+        }
+    };
+} // namespace mean_field::operators::detail
+
+export namespace mean_field::operators {
+    /*
+     * Runtime enforcement currently supports a pointwise pressure constraint
+     * whose row field is also its sole state field. The concept is expressed
+     * entirely in compiled-constraint metadata: no thermodynamic carrier or
+     * concrete field is selected by this prepared layer.
+     */
+    template <typename Candidate>
+    concept SingleFieldPressureSurfaceConstraint =
+        requires {
+            typename std::remove_cvref_t<Candidate>::PhysicalQuantity;
+            typename std::remove_cvref_t<Candidate>::CarrierQuantity;
+            typename std::remove_cvref_t<Candidate>::CarrierField;
+            typename std::remove_cvref_t<Candidate>::SurfaceDependencies;
+        } && std::same_as<typename std::remove_cvref_t<Candidate>::PhysicalQuantity, eos::quantity::Pressure> &&
+        std::same_as<
+            typename std::remove_cvref_t<Candidate>::SurfaceDependencies::RowField,
+            typename std::remove_cvref_t<Candidate>::CarrierField> &&
+        std::same_as<
+            typename std::remove_cvref_t<Candidate>::SurfaceDependencies::StateFieldTypes,
+            field::TypeList<typename std::remove_cvref_t<Candidate>::CarrierField>>;
+
+    template <typename Candidate, typename Field>
+    concept SingleFieldPressureSurfaceConstraintFor =
+        SingleFieldPressureSurfaceConstraint<Candidate> &&
+        std::same_as<typename std::remove_cvref_t<Candidate>::SurfaceDependencies::RowField, Field>;
+
+    /*
+     * Non-owning runtime bridge for a statically compiled pressure constraint.
+     * There is one function-pointer dispatch per complete row application;
+     * the concrete loop remains templated so EOS operations can be inlined.
+     */
+    class PressureSurfaceConstraintView final {
+    public:
+        template <SingleFieldPressureSurfaceConstraint Constraint>
+        explicit PressureSurfaceConstraintView(const Constraint &constraint) noexcept
+            : m_constraint(std::addressof(constraint)),
+              m_applyResidualRows(&applyResidualRows<Constraint>),
+              m_applyJacobianRows(&applyJacobianRows<Constraint>),
+              m_descriptor(constraint.descriptor()) {
+        }
+
+        void ApplyResidualRows(
+            const mfem::Vector &surfaceState,
+            const field::FieldBoundaryDofMap &surfaceRows,
+            mfem::Vector &rowResidual
+        ) const {
+            m_applyResidualRows(m_constraint, surfaceState, surfaceRows, rowResidual);
+        }
+
+        void ApplyJacobianRows(
+            const mfem::Vector &surfaceState,
+            const field::FieldBoundaryDofMap &surfaceRows,
+            const mfem::Vector &stateVariation,
+            mfem::Vector &rowAction
+        ) const {
+            m_applyJacobianRows(m_constraint, surfaceState, surfaceRows, stateVariation, rowAction);
+        }
+
+        [[nodiscard]] surface::PressureSurfaceDescriptor descriptor() const noexcept {
+            return m_descriptor;
+        }
+
+    private:
+        using ApplyResidualRowsFunction = void (*)(
+            const void *,
+            const mfem::Vector &,
+            const field::FieldBoundaryDofMap &,
+            mfem::Vector &
+        );
+        using ApplyJacobianRowsFunction = void (*)(
+            const void *,
+            const mfem::Vector &,
+            const field::FieldBoundaryDofMap &,
+            const mfem::Vector &,
+            mfem::Vector &
+        );
+
+        template <SingleFieldPressureSurfaceConstraint Constraint>
+        static void applyResidualRows(
+            const void *constraint,
+            const mfem::Vector &surfaceState,
+            const field::FieldBoundaryDofMap &surfaceRows,
+            mfem::Vector &rowResidual
+        ) {
+            using CarrierQuantity = typename Constraint::CarrierQuantity;
+
+            for (int surfaceIndex = 0; surfaceIndex < surfaceRows.size(); ++surfaceIndex) {
+                const detail::SingleQuantitySurfaceState<CarrierQuantity> state{
+                    eos::QuantityValue<CarrierQuantity>{surfaceState(surfaceIndex)}
+                };
+                rowResidual(surfaceRows.reduced_dofs()[surfaceIndex]) =
+                    static_cast<const Constraint *>(constraint)->residual(state);
+            }
+        }
+
+        template <SingleFieldPressureSurfaceConstraint Constraint>
+        static void applyJacobianRows(
+            const void *constraint,
+            const mfem::Vector &surfaceState,
+            const field::FieldBoundaryDofMap &surfaceRows,
+            const mfem::Vector &stateVariation,
+            mfem::Vector &rowAction
+        ) {
+            using CarrierQuantity = typename Constraint::CarrierQuantity;
+
+            for (int surfaceIndex = 0; surfaceIndex < surfaceRows.size(); ++surfaceIndex) {
+                const int reducedDof = surfaceRows.reduced_dofs()[surfaceIndex];
+                const detail::SingleQuantitySurfaceState<CarrierQuantity> state{
+                    eos::QuantityValue<CarrierQuantity>{surfaceState(surfaceIndex)}
+                };
+                const detail::SingleQuantitySurfaceState<CarrierQuantity> variation{
+                    eos::QuantityValue<CarrierQuantity>{stateVariation(reducedDof)}
+                };
+                rowAction(reducedDof) = static_cast<const Constraint *>(constraint)->jacobianAction(state, variation);
+            }
+        }
+
+        const void *m_constraint;
+        ApplyResidualRowsFunction m_applyResidualRows;
+        ApplyJacobianRowsFunction m_applyJacobianRows;
+        surface::PressureSurfaceDescriptor m_descriptor;
+    };
+
+    struct PreparedSurfaceConstraintReport final {
+        bool cachedSurfaceState{false};
+
+        [[nodiscard]] bool DidAnyWork() const noexcept {
+            return cachedSurfaceState;
+        }
+    };
+
+    class PreparedPressureSurfaceConstraint final {
+    public:
+        PreparedPressureSurfaceConstraint(
+            field::FieldBoundaryDofMap surfaceRows,
+            const PressureSurfaceConstraintView constraint
+        )
+            : m_surfaceRows(std::move(surfaceRows)),
+              m_constraint(constraint),
+              m_surfaceState(m_surfaceRows.size()) {
+        }
+
+        [[nodiscard]] PreparedSurfaceConstraintReport Prepare(
+            const mfem::Vector &reducedState,
+            const bool stateChanged
+        ) {
+            MFEM_VERIFY(
+                reducedState.Size() == m_surfaceRows.field_size(),
+                "The pressure surface constraint received a state vector with the wrong size."
+            );
+
+            PreparedSurfaceConstraintReport report;
+            if (!m_isPrepared || stateChanged) {
+                for (int surfaceIndex = 0; surfaceIndex < m_surfaceRows.size(); ++surfaceIndex) {
+                    const double value = reducedState(m_surfaceRows.reduced_dofs()[surfaceIndex]);
+                    MFEM_VERIFY(std::isfinite(value), "The pressure surface constraint received non-finite state.");
+                    m_surfaceState(surfaceIndex) = value;
+                }
+                report.cachedSurfaceState = true;
+            }
+
+            m_isPrepared = true;
+            return report;
+        }
+
+        void ApplyResidualRows(mfem::Vector &rowResidual) const {
+            VerifyPrepared();
+            MFEM_VERIFY(
+                rowResidual.Size() == m_surfaceRows.field_size(),
+                "The pressure surface constraint received a residual vector with the wrong size."
+            );
+            m_constraint.ApplyResidualRows(m_surfaceState, m_surfaceRows, rowResidual);
+        }
+
+        void ApplyJacobianRows(
+            const mfem::Vector &stateVariation,
+            mfem::Vector &rowAction
+        ) const {
+            VerifyPrepared();
+            MFEM_VERIFY(
+                stateVariation.Size() == m_surfaceRows.field_size() && rowAction.Size() == m_surfaceRows.field_size(),
+                "The pressure surface constraint received a Jacobian vector with the wrong size."
+            );
+            m_constraint.ApplyJacobianRows(m_surfaceState, m_surfaceRows, stateVariation, rowAction);
+        }
+
+        [[nodiscard]] bool IsPrepared() const noexcept {
+            return m_isPrepared;
+        }
+
+        [[nodiscard]] const field::FieldBoundaryDofMap &GetSurfaceRows() const noexcept {
+            return m_surfaceRows;
+        }
+
+        [[nodiscard]] surface::PressureSurfaceDescriptor GetPhysicalCondition() const noexcept {
+            return m_constraint.descriptor();
+        }
+
+    private:
+        void VerifyPrepared() const {
+            MFEM_VERIFY(m_isPrepared, "The pressure surface constraint must be prepared before row application.");
+        }
+
+        field::FieldBoundaryDofMap m_surfaceRows;
+        PressureSurfaceConstraintView m_constraint;
+        mfem::Vector m_surfaceState;
+        bool m_isPrepared{false};
+    };
+} // namespace mean_field::operators

libmeanfield/interface/surface/compiled.cppm

@@ -0,0 +1,66 @@
+module;
+
+export module mean_field:surface.compiled;
+
+export import :eos.pressure_surface;
+export import :surface.constant;
+export import :surface.dependencies;
+
+export namespace mean_field::surface {
+    template <
+        eos::EquationOfStateModel EquationOfState,
+        SurfaceConstraintFormulationType Formulation,
+        eos::ThermodynamicRelationType SelectedRelation,
+        typename Dependencies>
+    class CompiledPressureSurfaceConstraint final {
+    public:
+        using PhysicalCondition   = ConstantPressureSurface;
+        using PhysicalQuantity    = eos::quantity::Pressure;
+        using CarrierQuantity     = typename Formulation::CarrierQuantity;
+        using CarrierField        = typename Formulation::CarrierField;
+        using Relation            = SelectedRelation;
+        using SurfaceDependencies = Dependencies;
+
+        CompiledPressureSurfaceConstraint(
+            const ConstantPressureSurface condition,
+            const EquationOfState &equationOfState
+        ) noexcept
+            : m_condition(condition),
+              m_resolvedRelation(
+                  equationOfState,
+                  condition.targetPressure()
+              ) {
+        }
+
+        [[nodiscard]] eos::PressureValue targetPressure() const noexcept {
+            return m_condition.targetPressure();
+        }
+
+        [[nodiscard]] PressureSurfaceDescriptor descriptor() const noexcept {
+            return m_condition.descriptor();
+        }
+
+        [[nodiscard]] static constexpr RuntimeSurfaceConstraintDependencies runtimeDependencies() noexcept {
+            return SurfaceDependencies::runtimeDescription();
+        }
+
+        template <typename SurfaceState> [[nodiscard]] double residual(const SurfaceState &state) const {
+            return state.value(CarrierQuantity{}).value() - m_resolvedRelation.requiredCarrierValue(state).value();
+        }
+
+        template <
+            typename SurfaceState,
+            typename SurfaceVariation>
+        [[nodiscard]] double jacobianAction(
+            const SurfaceState &state,
+            const SurfaceVariation &variation
+        ) const {
+            return variation.value(CarrierQuantity{}).value() -
+                   m_resolvedRelation.carrierCorrectionJacobianAction(state, variation);
+        }
+
+    private:
+        ConstantPressureSurface m_condition;
+        eos::ResolvedPressureSurfaceRelation<EquationOfState, Relation> m_resolvedRelation;
+    };
+} // namespace mean_field::surface

libmeanfield/interface/surface/compiler.cppm

@@ -0,0 +1,143 @@
+module;
+
+#include <cstddef>
+#include <tuple>
+#include <type_traits>
+
+export module mean_field:surface.compiler;
+
+export import :surface.compiled;
+
+export namespace mean_field::surface {
+    namespace detail {
+        template <typename RelationType, typename Formulation, typename EquationOfState>
+        struct PressureSurfaceRelationMatches : std::false_type { };
+
+        template <typename OutputQuantity, typename... InputQuantities, typename Formulation, typename EquationOfState>
+        struct PressureSurfaceRelationMatches<
+            eos::Relation<OutputQuantity, InputQuantities...>,
+            Formulation,
+            EquationOfState>
+            : std::bool_constant<
+                  std::same_as<OutputQuantity, typename Formulation::CarrierQuantity> &&
+                  (std::same_as<eos::quantity::Pressure, InputQuantities> || ...) &&
+                  ((std::same_as<eos::quantity::Pressure, InputQuantities> ||
+                    (surfaceBindingCount<typename Formulation::StateBindings, InputQuantities> == 1 &&
+                     eos::SupportsPartialDerivative<
+                         EquationOfState,
+                         eos::Relation<OutputQuantity, InputQuantities...>,
+                         InputQuantities>)) &&
+                   ...)> { };
+
+        template <typename Catalog, typename Formulation, typename EquationOfState>
+        struct MatchingPressureSurfaceRelations;
+
+        template <typename... Relations, typename Formulation, typename EquationOfState>
+        struct MatchingPressureSurfaceRelations<eos::RelationCatalog<Relations...>, Formulation, EquationOfState> {
+            using Tuple                        = decltype(std::tuple_cat(
+                std::conditional_t<
+                    PressureSurfaceRelationMatches<Relations, Formulation, EquationOfState>::value,
+                    std::tuple<Relations>,
+                    std::tuple<>>{}...
+            ));
+
+            static constexpr std::size_t count = std::tuple_size_v<Tuple>;
+        };
+
+        template <std::size_t Count, typename Tuple> struct UniquePressureSurfaceRelation {
+            using Type = void;
+        };
+
+        template <typename Tuple> struct UniquePressureSurfaceRelation<1, Tuple> {
+            using Type = std::tuple_element_t<0, Tuple>;
+        };
+
+        template <typename Dependencies, typename Field> struct AppendSurfaceDependency;
+
+        template <typename RowField, typename... StateFields, typename Field>
+        struct AppendSurfaceDependency<SurfaceConstraintDependencies<RowField, StateFields...>, Field> {
+            using Type = SurfaceConstraintDependencies<RowField, StateFields..., Field>;
+        };
+
+        template <typename Dependencies, typename InputQuantity, typename Bindings>
+        struct AppendPressureSurfaceInputDependency {
+            using Type =
+                typename AppendSurfaceDependency<Dependencies, SurfaceFieldForQuantityT<Bindings, InputQuantity>>::Type;
+        };
+
+        template <typename Dependencies, typename Bindings>
+        struct AppendPressureSurfaceInputDependency<Dependencies, eos::quantity::Pressure, Bindings> {
+            using Type = Dependencies;
+        };
+
+        template <typename Dependencies, typename Bindings, typename... InputQuantities>
+        struct AppendPressureSurfaceInputDependencies;
+
+        template <typename Dependencies, typename Bindings>
+        struct AppendPressureSurfaceInputDependencies<Dependencies, Bindings> {
+            using Type = Dependencies;
+        };
+
+        template <typename Dependencies, typename Bindings, typename FirstInput, typename... RemainingInputs>
+        struct AppendPressureSurfaceInputDependencies<Dependencies, Bindings, FirstInput, RemainingInputs...> {
+            using WithFirst = typename AppendPressureSurfaceInputDependency<Dependencies, FirstInput, Bindings>::Type;
+            using Type = typename AppendPressureSurfaceInputDependencies<WithFirst, Bindings, RemainingInputs...>::Type;
+        };
+
+        template <typename RelationType, typename Formulation> struct PressureSurfaceDependenciesForRelation;
+
+        template <typename OutputQuantity, typename... InputQuantities, typename Formulation>
+        struct PressureSurfaceDependenciesForRelation<eos::Relation<OutputQuantity, InputQuantities...>, Formulation> {
+            using InitialDependencies =
+                SurfaceConstraintDependencies<typename Formulation::CarrierField, typename Formulation::CarrierField>;
+            using Type = typename AppendPressureSurfaceInputDependencies<
+                InitialDependencies,
+                typename Formulation::StateBindings,
+                InputQuantities...>::Type;
+        };
+
+        template <SurfaceConstraintFormulationType Formulation, eos::EquationOfStateModel EquationOfState>
+        struct PressureSurfaceCompilation {
+            using Matches =
+                MatchingPressureSurfaceRelations<typename EquationOfState::Relations, Formulation, EquationOfState>;
+            using Relation = typename UniquePressureSurfaceRelation<Matches::count, typename Matches::Tuple>::Type;
+        };
+
+        template <SurfaceConstraintFormulationType Formulation, eos::EquationOfStateModel EquationOfState>
+            requires(PressureSurfaceCompilation<Formulation, EquationOfState>::Matches::count == 1)
+        struct CompiledPressureSurfaceConstraintType {
+            using Compilation  = PressureSurfaceCompilation<Formulation, EquationOfState>;
+            using Relation     = typename Compilation::Relation;
+            using Dependencies = typename PressureSurfaceDependenciesForRelation<Relation, Formulation>::Type;
+            using Type = CompiledPressureSurfaceConstraint<EquationOfState, Formulation, Relation, Dependencies>;
+        };
+    } // namespace detail
+
+    template <typename Formulation, typename EquationOfState>
+    concept PressureSurfaceCompilable =
+        SurfaceConstraintFormulationType<Formulation> && eos::EquationOfStateModel<EquationOfState> &&
+        (detail::PressureSurfaceCompilation<std::remove_cvref_t<Formulation>, std::remove_cvref_t<EquationOfState>>::
+             Matches::count == 1);
+
+    template <SurfaceConstraintFormulationType Formulation, eos::EquationOfStateModel EquationOfState>
+        requires PressureSurfaceCompilable<Formulation, EquationOfState>
+    using CompiledPressureSurfaceConstraintT = typename detail::CompiledPressureSurfaceConstraintType<
+        std::remove_cvref_t<Formulation>,
+        std::remove_cvref_t<EquationOfState>>::Type;
+
+    template <
+        SurfaceConstraintFormulationType Formulation,
+        eos::EquationOfStateModel EquationOfState>
+        requires PressureSurfaceCompilable<
+            Formulation,
+            EquationOfState>
+    [[nodiscard]] CompiledPressureSurfaceConstraintT<
+        Formulation,
+        EquationOfState>
+    compilePressureSurfaceConstraint(
+        const ConstantPressureSurface condition,
+        const EquationOfState &equationOfState
+    ) noexcept {
+        return CompiledPressureSurfaceConstraintT<Formulation, EquationOfState>{condition, equationOfState};
+    }
+} // namespace mean_field::surface

libmeanfield/interface/surface/constant.cppm

@@ -0,0 +1,65 @@
+module;
+
+#include <cmath>
+#include <format>
+#include <stdexcept>
+#include <type_traits>
+
+export module mean_field:surface.constant;
+
+export import :eos.quantities;
+
+export namespace mean_field::surface {
+    struct PressureSurfaceDescriptor final {
+        double targetPressure;
+    };
+
+    /*
+     * The only physical surface prescription currently supported by
+     * MeanField. It says nothing about which thermodynamic variable appears
+     * in a nonlinear state vector; resolving pressure into that representation
+     * is an EOS responsibility.
+     */
+    class ConstantPressureSurface final {
+    public:
+        using PhysicalQuantity = eos::quantity::Pressure;
+        using TargetValue      = eos::PressureValue;
+
+        explicit ConstantPressureSurface(const TargetValue targetPressure) : m_targetPressure(targetPressure) {
+            if (!std::isfinite(targetPressure.value())) {
+                throw std::invalid_argument(
+                    std::format(
+                        "The target surface pressure must be finite. Instead P = {} was provided.",
+                        targetPressure.value()
+                    )
+                );
+            }
+            if (targetPressure.value() < 0.0) {
+                throw std::invalid_argument(
+                    std::format(
+                        "The target surface pressure must be non-negative. Instead P = {} was provided.",
+                        targetPressure.value()
+                    )
+                );
+            }
+        }
+
+        [[nodiscard]] TargetValue targetPressure() const noexcept {
+            return m_targetPressure;
+        }
+
+        [[nodiscard]] PressureSurfaceDescriptor descriptor() const noexcept {
+            return PressureSurfaceDescriptor{.targetPressure = m_targetPressure.value()};
+        }
+
+    private:
+        TargetValue m_targetPressure;
+    };
+
+    template <typename Candidate>
+    concept ConstantPressureSurfaceType = std::same_as<std::remove_cvref_t<Candidate>, ConstantPressureSurface>;
+
+    // Familiar physical terminology retained as a synonym, not as a second
+    // surface-condition type.
+    using Isobaric                      = ConstantPressureSurface;
+} // namespace mean_field::surface

libmeanfield/interface/surface/dependencies.cppm

@@ -0,0 +1,186 @@
+module;
+
+#include <array>
+#include <concepts>
+#include <cstddef>
+#include <span>
+#include <string_view>
+#include <type_traits>
+
+export module mean_field:surface.dependencies;
+
+export import :eos.relations;
+export import :field.registry;
+
+export namespace mean_field::surface {
+    template <typename Candidate>
+    concept SurfaceFieldType = requires {
+        { Candidate::name } -> std::convertible_to<std::string_view>;
+    } && (std::string_view{Candidate::name}.size() > 0);
+
+    class SurfaceFieldId final {
+    public:
+        explicit constexpr SurfaceFieldId(const std::string_view name) noexcept : m_name(name) {
+        }
+
+        [[nodiscard]] constexpr std::string_view name() const noexcept {
+            return m_name;
+        }
+
+        [[nodiscard]] friend constexpr bool operator==(
+            const SurfaceFieldId &,
+            const SurfaceFieldId &
+        ) noexcept = default;
+
+    private:
+        std::string_view m_name;
+    };
+
+    template <SurfaceFieldType Field> inline constexpr SurfaceFieldId surfaceFieldId{std::string_view{Field::name}};
+
+    template <eos::ThermodynamicQuantityType ThermodynamicQuantity, SurfaceFieldType Field>
+    struct SurfaceStateBinding final {
+        using Quantity  = ThermodynamicQuantity;
+        using FieldType = Field;
+    };
+
+    template <typename... Bindings> struct SurfaceStateBindings final { };
+
+    namespace detail {
+        template <typename... Types> struct SurfaceTypesAreUnique : std::true_type { };
+
+        template <typename First, typename... Remaining>
+        struct SurfaceTypesAreUnique<First, Remaining...>
+            : std::bool_constant<
+                  (!std::same_as<First, Remaining> && ...) && SurfaceTypesAreUnique<Remaining...>::value> { };
+
+        template <typename Bindings> struct SurfaceBindingsAreValid : std::false_type { };
+
+        template <typename... Bindings>
+        struct SurfaceBindingsAreValid<SurfaceStateBindings<Bindings...>>
+            : std::bool_constant<
+                  (sizeof...(Bindings) > 0) &&
+                  (requires {
+            typename Bindings::Quantity;
+            typename Bindings::FieldType;
+                  } && ...) &&
+                  (eos::ThermodynamicQuantityType<
+                       typename Bindings::Quantity> && ...) &&
+                  (SurfaceFieldType<typename Bindings::FieldType> && ...) &&
+                  SurfaceTypesAreUnique<
+                      typename Bindings::Quantity...>::value> { };
+
+                  template <typename Bindings, typename Quantity> struct SurfaceBindingCount;
+
+                  template <typename Quantity, typename... Bindings>
+                  struct SurfaceBindingCount<SurfaceStateBindings<Bindings...>, Quantity>
+                      : std::integral_constant<
+                            std::size_t,
+                            (std::size_t{0} + ... +
+                             (std::same_as<Quantity, typename Bindings::Quantity> ? std::size_t{1} : std::size_t{0}))> {
+                  };
+
+                  template <typename Bindings, typename Quantity> struct SurfaceFieldForQuantity;
+
+                  template <typename Quantity, typename First, typename... Remaining>
+                  struct SurfaceFieldForQuantity<SurfaceStateBindings<First, Remaining...>, Quantity>
+                      : std::conditional_t<
+                            std::same_as<Quantity, typename First::Quantity>,
+                            std::type_identity<typename First::FieldType>,
+                            SurfaceFieldForQuantity<SurfaceStateBindings<Remaining...>, Quantity>> { };
+
+                  template <typename Candidate, std::size_t CarrierBindingCount>
+                  struct CarrierFieldMatchesSurfaceBinding : std::false_type { };
+
+                  template <typename Candidate>
+                  struct CarrierFieldMatchesSurfaceBinding<Candidate, 1>
+                      : std::bool_constant<std::same_as<
+                            typename SurfaceFieldForQuantity<
+                                typename Candidate::StateBindings,
+                                typename Candidate::CarrierQuantity>::type,
+                            typename Candidate::CarrierField>> { };
+
+                  template <
+                      typename Candidate,
+                      bool BindingsAreValid = SurfaceBindingsAreValid<typename Candidate::StateBindings>::value>
+                  struct FormulationBindingsMatchCarrier : std::false_type { };
+
+                  template <typename Candidate>
+                  struct FormulationBindingsMatchCarrier<Candidate, true>
+                      : CarrierFieldMatchesSurfaceBinding<
+                            Candidate,
+                            SurfaceBindingCount<
+                                typename Candidate::StateBindings,
+                                typename Candidate::CarrierQuantity>::value> { };
+
+                  template <typename Candidate, typename = void>
+                  struct IsSurfaceConstraintFormulation : std::false_type { };
+
+                  template <typename Candidate>
+                  struct IsSurfaceConstraintFormulation<
+                      Candidate,
+                      std::void_t<
+                          typename Candidate::CarrierQuantity,
+                          typename Candidate::CarrierField,
+                          typename Candidate::StateBindings>>
+                      : std::bool_constant<
+                            eos::ThermodynamicQuantityType<typename Candidate::CarrierQuantity> &&
+                            SurfaceFieldType<typename Candidate::CarrierField> &&
+                            FormulationBindingsMatchCarrier<Candidate>::value> { };
+    } // namespace detail
+
+    template <typename Candidate>
+    concept ValidSurfaceStateBindings = detail::SurfaceBindingsAreValid<std::remove_cv_t<Candidate>>::value;
+
+    template <ValidSurfaceStateBindings Bindings, typename Quantity>
+    inline constexpr std::size_t surfaceBindingCount = detail::SurfaceBindingCount<Bindings, Quantity>::value;
+
+    template <ValidSurfaceStateBindings Bindings, typename Quantity>
+        requires(surfaceBindingCount<Bindings, Quantity> == 1)
+    using SurfaceFieldForQuantityT = typename detail::SurfaceFieldForQuantity<Bindings, Quantity>::type;
+
+    template <
+        eos::ThermodynamicQuantityType CarrierThermodynamicQuantity,
+        SurfaceFieldType CarrierFieldType,
+        ValidSurfaceStateBindings Bindings>
+        requires(
+            surfaceBindingCount<Bindings, CarrierThermodynamicQuantity> == 1 &&
+            std::same_as<SurfaceFieldForQuantityT<Bindings, CarrierThermodynamicQuantity>, CarrierFieldType>
+        )
+    struct SurfaceConstraintFormulation final {
+        using CarrierQuantity = CarrierThermodynamicQuantity;
+        using CarrierField    = CarrierFieldType;
+        using StateBindings   = Bindings;
+    };
+
+    using BarotropicSurfaceFormulation = SurfaceConstraintFormulation<
+        eos::quantity::SpecificEnthalpy,
+        field::Enthalpy,
+        SurfaceStateBindings<SurfaceStateBinding<eos::quantity::SpecificEnthalpy, field::Enthalpy>>>;
+
+    template <typename Candidate>
+    concept SurfaceConstraintFormulationType =
+        detail::IsSurfaceConstraintFormulation<std::remove_cv_t<Candidate>>::value;
+
+    struct RuntimeSurfaceConstraintDependencies final {
+        SurfaceFieldId residualRowField;
+        std::span<const SurfaceFieldId> stateFields;
+    };
+
+    template <SurfaceFieldType ResidualField, SurfaceFieldType... StateFields>
+    struct SurfaceConstraintDependencies final {
+        using RowField        = ResidualField;
+        using StateFieldTypes = field::TypeList<StateFields...>;
+
+        inline static constexpr std::array<SurfaceFieldId, sizeof...(StateFields)> runtimeStateFields{
+            surfaceFieldId<StateFields>...
+        };
+
+        [[nodiscard]] static constexpr RuntimeSurfaceConstraintDependencies runtimeDescription() noexcept {
+            return RuntimeSurfaceConstraintDependencies{
+                .residualRowField = surfaceFieldId<ResidualField>,
+                .stateFields      = std::span<const SurfaceFieldId>{runtimeStateFields}
+            };
+        }
+    };
+} // namespace mean_field::surface

libmeanfield/interface/surface/isobaric.cppm

@@ -1,64 +0,0 @@
-module;
-
-#include <cmath>
-#include <format>
-#include <stdexcept>
-
-export module mean_field:surface.isobaric;
-
-export import :surface.base;
-
-export namespace mean_field::surface {
-    class Isobaric final : public SurfaceBase {
-    public:
-        explicit Isobaric(const double targetPressure = 0.0) : m_targetPressure(targetPressure) {
-            validateTargetPressure();
-        }
-
-        [[nodiscard]] double targetPressure() const noexcept {
-            return m_targetPressure;
-        }
-
-        [[nodiscard]] ResolvedSurfaceCondition
-        resolve(const mean_field::eos::EquationOfState &equationOfState) const override {
-            return ResolvedSurfaceCondition{resolveTargetEnthalpy(equationOfState)};
-        }
-
-        void validate(const mean_field::eos::EquationOfState &equationOfState) const override {
-            static_cast<void>(resolveTargetEnthalpy(equationOfState));
-        }
-
-    private:
-        [[nodiscard]] double resolveTargetEnthalpy(const mean_field::eos::EquationOfState &equationOfState) const {
-            validateTargetPressure();
-
-            const double targetEnthalpy = equationOfState.enthalpy_from_pressure(m_targetPressure);
-
-            if (!std::isfinite(targetEnthalpy) || targetEnthalpy < 0.0) {
-                throw std::domain_error(
-                    std::format(
-                        "The equation of state resolved the isobaric "
-                        "target P = {} to the invalid enthalpy h = {}.",
-                        m_targetPressure, targetEnthalpy
-                    )
-                );
-            }
-
-            return targetEnthalpy;
-        }
-
-        void validateTargetPressure() const {
-            if (!std::isfinite(m_targetPressure) || m_targetPressure < 0.0) {
-                throw std::invalid_argument(
-                    std::format(
-                        "The target surface pressure must be finite and "
-                        "non-negative. Instead P = {} was provided.",
-                        m_targetPressure
-                    )
-                );
-            }
-        }
-
-        double m_targetPressure;
-    };
-} // namespace mean_field::surface

libmeanfield/interface/surface/surface_base.cppm

@@ -1,53 +0,0 @@
-module;
-
-#include <cmath>
-#include <stdexcept>
-
-export module mean_field:surface.base;
-
-export import :eos.base;
-
-export namespace mean_field::surface {
-    struct ResolvedSurfaceCondition final {
-        double targetEnthalpy{0.0};
-
-        explicit ResolvedSurfaceCondition(const double requestedTargetEnthalpy)
-            : targetEnthalpy(requestedTargetEnthalpy) {
-            if (!std::isfinite(targetEnthalpy) || targetEnthalpy < 0.0) {
-                throw std::invalid_argument(
-                    "A resolved surface enthalpy must be finite and "
-                    "non-negative."
-                );
-            }
-        }
-
-        [[nodiscard]] double residual(const double enthalpy) const {
-            if (!std::isfinite(enthalpy)) {
-                throw std::invalid_argument("A surface enthalpy value must be finite.");
-            }
-
-            return enthalpy - targetEnthalpy;
-        }
-
-        [[nodiscard]] static double jacobianAction(const double enthalpyVariation) {
-            if (!std::isfinite(enthalpyVariation)) {
-                throw std::invalid_argument("A surface enthalpy variation must be finite.");
-            }
-
-            return enthalpyVariation;
-        }
-    };
-
-    class SurfaceBase {
-    public:
-        virtual ~SurfaceBase() = default;
-
-        [[nodiscard]] virtual ResolvedSurfaceCondition
-        resolve(const mean_field::eos::EquationOfState &equationOfState) const               = 0;
-
-        virtual void validate(const mean_field::eos::EquationOfState &equationOfState) const = 0;
-
-    protected:
-        SurfaceBase() = default;
-    };
-} // namespace mean_field::surface

libmeanfield/interface/utils/misc.cppm

@@ -11,82 +11,90 @@ export module mean_field:utils.misc;
 import :utils.domain;
 
 export namespace mean_field::utils {
-constexpr double APPROX_MAX_ACCEPTABLE_POTENTIAL_ERROR_SI_BURNING = 1e-4;
+    constexpr double APPROX_MAX_ACCEPTABLE_POTENTIAL_ERROR_SI_BURNING = 1e-4;
 
-bool is_vacuum(const mfem::ElementTransformation &Tr,
-               mfem::Array<mfem::Vector *> elvec) {
-  using Schema = domain::CoreEnvelopeVacuumDomainSchema;
+    bool is_vacuum(
+        const mfem::ElementTransformation &Tr,
+        mfem::Array<mfem::Vector *> elvec
+    ) {
+        using Schema = domain::CoreEnvelopeVacuumDomainSchema;
 
-  if (Schema::template attribute_belongs_to<domain::Vacuum>(Tr.Attribute)) {
-    const int size_elvec = elvec.Size();
-    for (int i = 0; i < size_elvec; i++) {
-      if (elvec[i]) {
-        *elvec[i] = 0.0;
-      }
-    }
-    return true;
-  }
-  return false;
-}
-
-bool is_vacuum(const mfem::ElementTransformation &Tr,
-               const mfem::Array2D<mfem::DenseMatrix *> &elmats) {
-  using Schema = domain::CoreEnvelopeVacuumDomainSchema;
-
-  if (Schema::template attribute_belongs_to<domain::Vacuum>(Tr.Attribute)) {
-    const int cols = elmats.NumCols();
-    const int rows = elmats.NumRows();
-    for (int rowID = 0; rowID < rows; rowID++) {
-      for (int colID = 0; colID < cols; colID++) {
-        if (elmats(rowID, colID)) {
-          *elmats(rowID, colID) = 0.0;
+        if (Schema::template attribute_belongs_to<domain::Vacuum>(Tr.Attribute)) {
+            const int size_elvec = elvec.Size();
+            for (int i = 0; i < size_elvec; i++) {
+                if (elvec[i]) {
+                    *elvec[i] = 0.0;
+                }
+            }
+            return true;
         }
-      }
+        return false;
     }
-    return true;
-  }
-  return false;
-}
 
-constexpr std::string_view ANSI_GREEN = "\033[32m";
-constexpr std::string_view ANSI_RED = "\033[31m";
-constexpr std::string_view ANSI_YELLOW = "\033[33m";
-constexpr std::string_view ANSI_BLUE = "\033[34m";
-constexpr std::string_view ANSI_MAGENTA = "\033[35m";
-constexpr std::string_view ANSI_CYAN = "\033[36m";
-constexpr std::string_view ANSI_RESET = "\033[0m";
-constexpr std::string_view ANSI_BCYAN = "\033[1;36m";
+    bool is_vacuum(
+        const mfem::ElementTransformation &Tr,
+        const mfem::Array2D<mfem::DenseMatrix *> &elmats
+    ) {
+        using Schema = domain::CoreEnvelopeVacuumDomainSchema;
 
-constexpr double G = 1.0;
-constexpr double MASS = 1.0;
-constexpr double RADIUS = 1.0;
+        if (Schema::template attribute_belongs_to<domain::Vacuum>(Tr.Attribute)) {
+            const int cols = elmats.NumCols();
+            const int rows = elmats.NumRows();
+            for (int rowID = 0; rowID < rows; rowID++) {
+                for (int colID = 0; colID < cols; colID++) {
+                    if (elmats(rowID, colID)) {
+                        *elmats(rowID, colID) = 0.0;
+                    }
+                }
+            }
+            return true;
+        }
+        return false;
+    }
 
-[[maybe_unused]] constexpr char HOST[10] = "localhost";
-[[maybe_unused]] constexpr int PORT = 19916;
+    constexpr std::string_view ANSI_GREEN    = "\033[32m";
+    constexpr std::string_view ANSI_RED      = "\033[31m";
+    constexpr std::string_view ANSI_YELLOW   = "\033[33m";
+    constexpr std::string_view ANSI_BLUE     = "\033[34m";
+    constexpr std::string_view ANSI_MAGENTA  = "\033[35m";
+    constexpr std::string_view ANSI_CYAN     = "\033[36m";
+    constexpr std::string_view ANSI_RESET    = "\033[0m";
+    constexpr std::string_view ANSI_BCYAN    = "\033[1;36m";
 
-template <typename T>
-concept is_xad = std::is_same_v<T, xad::AReal<long double>> ||
-                 std::is_same_v<T, xad::AReal<double>> ||
-                 std::is_same_v<T, xad::AReal<float>>;
+    constexpr double G                       = 1.0;
+    constexpr double MASS                    = 1.0;
+    constexpr double RADIUS                  = 1.0;
 
-template <typename T>
-concept is_real = std::is_floating_point_v<T> || is_xad<T>;
+    [[maybe_unused]] constexpr char HOST[10] = "localhost";
+    [[maybe_unused]] constexpr int PORT      = 19916;
 
-template <is_real T>
-using EOS_P = std::function<T(const T &rho, const T &temp)>;
+    template <typename T>
+    concept is_xad = std::is_same_v<T, xad::AReal<long double>> || std::is_same_v<T, xad::AReal<double>> ||
+                     std::is_same_v<T, xad::AReal<float>>;
 
-enum class DOMAINS : uint8_t {
-  CORE = 1 << 0,
-  ENVELOPE = 1 << 1,
-  VACUUM = 1 << 2,
-  STELLAR = CORE | ENVELOPE,
-  ALL = CORE | ENVELOPE | VACUUM
-};
+    template <typename T>
+    concept is_real                  = std::is_floating_point_v<T> || is_xad<T>;
 
-DOMAINS operator|(DOMAINS lhs, DOMAINS rhs);
+    template <is_real T> using EOS_P = std::function<T(const T &rho, const T &temp)>;
 
-DOMAINS operator&(DOMAINS lhs, DOMAINS rhs);
+    enum class DOMAINS : uint8_t {
+        CORE     = 1 << 0,
+        ENVELOPE = 1 << 1,
+        VACUUM   = 1 << 2,
+        STELLAR  = CORE | ENVELOPE,
+        ALL      = CORE | ENVELOPE | VACUUM
+    };
 
-int get_mesh_order(const mfem::Mesh &mesh);
+    DOMAINS operator|(
+        DOMAINS lhs,
+        DOMAINS rhs
+    );
+
+    DOMAINS operator&(
+        DOMAINS lhs,
+        DOMAINS rhs
+    );
+
+    int get_mesh_order(const mfem::Mesh &mesh);
 
 } // namespace mean_field::utils

tests/field/field_dof_map.cpp

@@ -94,6 +94,65 @@ namespace field_dof_map_test_utils {
         domain::RelationList<>>;
 } // namespace field_dof_map_test_utils
 
+TEST_CASE(
+    "Field Boundary DOF Map Selects The Stellar Surface In Reduced Field Ordering",
+    tags::surface_boundary_dof_topology
+) {
+    namespace domain             = mean_field::utils::domain;
+    namespace field              = mean_field::field;
+
+    mean_field::utils::Args args = test_utils::setup_args();
+    mean_field::fem::FEM f       = mean_field::fem::setup_fem(args.mesh_file, args, 0);
+    REQUIRE(f.okay());
+
+    const field::FieldDofMap enthalpyMap =
+        field::make_field_dof_map<field::Enthalpy, field_dof_map_test_utils::Schema>(*f.enthalpyFes);
+    const field::FieldBoundaryDofMap stellarSurface =
+        field::make_field_boundary_dof_map<field::Enthalpy, domain::StellarSurface, field_dof_map_test_utils::Schema>(
+            *f.enthalpyFes, enthalpyMap
+        );
+    CHECK(stellarSurface.field_size() == enthalpyMap.reduced_size());
+    CHECK(field_dof_map_test_utils::global_sum(stellarSurface.size()) > 0);
+    CHECK(
+        field_dof_map_test_utils::global_sum(stellarSurface.size()) <
+        field_dof_map_test_utils::global_sum(enthalpyMap.reduced_size())
+    );
+
+    for (const int reducedDof : stellarSurface.reduced_dofs()) {
+        CAPTURE(reducedDof);
+        CHECK(stellarSurface.contains(reducedDof));
+        CHECK(enthalpyMap.contains_true_dof(enthalpyMap.true_dof(reducedDof)));
+    }
+}
+
+TEST_CASE(
+    "Field Point DOF Map Selects One Vector Vertex At The Computational Origin",
+    tags::translational_centering_topology
+) {
+    namespace field              = mean_field::field;
+
+    mean_field::utils::Args args = test_utils::setup_args();
+    mean_field::fem::FEM f       = mean_field::fem::setup_fem(args.mesh_file, args, 0);
+    REQUIRE(f.okay());
+
+    const field::FieldDofMap displacementMap =
+        field::make_field_dof_map<field::Displacement, field_dof_map_test_utils::Schema>(*f.displacementFes);
+    mfem::Vector origin(f.mesh->SpaceDimension());
+    origin = 0.0;
+
+    const field::FieldPointDofMap centerRows =
+        field::make_field_point_dof_map<field::Displacement>(*f.displacementFes, displacementMap, origin, 1.0e-12);
+
+    CHECK(centerRows.field_size() == displacementMap.reduced_size());
+    CHECK(field_dof_map_test_utils::global_sum(centerRows.size()) == f.mesh->SpaceDimension());
+
+    for (const int reducedDof : centerRows.reduced_dofs()) {
+        CAPTURE(reducedDof);
+        CHECK(centerRows.contains(reducedDof));
+        CHECK(displacementMap.contains_true_dof(displacementMap.true_dof(reducedDof)));
+    }
+}
+
 TEST_CASE(
     "Field DOF Map Preserves Canonical Bidirectional Indexing",
     tags::field_dof_unit
@@ -523,9 +582,7 @@ TEST_CASE(
 
     STATIC_REQUIRE(field_dof_map_test_utils::CanMakeFieldDofGridFunctionAdapter<field::Displacement>);
 
-    STATIC_REQUIRE_FALSE(
-        field_dof_map_test_utils::CanMakeFieldDofGridFunctionAdapter<field::BarotropicConstant>
-    );
+    STATIC_REQUIRE_FALSE(field_dof_map_test_utils::CanMakeFieldDofGridFunctionAdapter<field::BarotropicConstant>);
 
     CHECK(true);
 }
@@ -750,9 +807,8 @@ TEST_CASE(
     mfem::Mesh serialMesh = field_dof_map_test_utils::make_split_mesh();
     mfem::ParMesh mesh(MPI_COMM_WORLD, serialMesh);
 
-    auto fec = field::Field<field::Density>::make_fec<field::Density::Scalar>(2);
-    auto finiteElementSpace =
-        field::Field<field::Density>::make_fespace<field::Density::Scalar>(mesh, *fec);
+    auto fec                = field::Field<field::Density>::make_fec<field::Density::Scalar>(2);
+    auto finiteElementSpace = field::Field<field::Density>::make_fespace<field::Density::Scalar>(mesh, *fec);
 
     REQUIRE(finiteElementSpace != nullptr);
 
@@ -796,9 +852,8 @@ TEST_CASE(
     mfem::Mesh serialMesh = field_dof_map_test_utils::make_split_mesh();
     mfem::ParMesh mesh(MPI_COMM_WORLD, serialMesh);
 
-    auto fec = field::Field<field::Enthalpy>::make_fec<field::Enthalpy::Scalar>(2);
-    auto finiteElementSpace =
-        field::Field<field::Enthalpy>::make_fespace<field::Enthalpy::Scalar>(mesh, *fec);
+    auto fec                = field::Field<field::Enthalpy>::make_fec<field::Enthalpy::Scalar>(2);
+    auto finiteElementSpace = field::Field<field::Enthalpy>::make_fespace<field::Enthalpy::Scalar>(mesh, *fec);
 
     REQUIRE(finiteElementSpace != nullptr);
 
@@ -849,9 +904,8 @@ TEST_CASE(
     mfem::Mesh serialMesh = field_dof_map_test_utils::make_split_mesh();
     mfem::ParMesh mesh(MPI_COMM_WORLD, serialMesh);
 
-    auto fec = field::Field<field::Density>::make_fec<field::Density::Scalar>(2);
-    auto finiteElementSpace =
-        field::Field<field::Density>::make_fespace<field::Density::Scalar>(mesh, *fec);
+    auto fec                = field::Field<field::Density>::make_fec<field::Density::Scalar>(2);
+    auto finiteElementSpace = field::Field<field::Density>::make_fespace<field::Density::Scalar>(mesh, *fec);
 
     REQUIRE(finiteElementSpace != nullptr);
 
@@ -900,9 +954,8 @@ TEST_CASE(
     mfem::Mesh serialMesh = field_dof_map_test_utils::make_split_mesh();
     mfem::ParMesh mesh(MPI_COMM_WORLD, serialMesh);
 
-    auto fec = field::Field<field::Displacement>::make_fec<field::Displacement::Vector>(2);
-    auto finiteElementSpace =
-        field::Field<field::Displacement>::make_fespace<field::Displacement::Vector>(mesh, *fec);
+    auto fec                = field::Field<field::Displacement>::make_fec<field::Displacement::Vector>(2);
+    auto finiteElementSpace = field::Field<field::Displacement>::make_fespace<field::Displacement::Vector>(mesh, *fec);
 
     REQUIRE(finiteElementSpace != nullptr);
 
@@ -939,13 +992,11 @@ TEST_CASE(
     mfem::Mesh serialMesh = field_dof_map_test_utils::make_split_mesh();
     mfem::ParMesh mesh(MPI_COMM_WORLD, serialMesh);
 
-    auto fec = field::Field<field::Density>::make_fec<field::Density::Scalar>(2);
-    auto finiteElementSpace =
-        field::Field<field::Density>::make_fespace<field::Density::Scalar>(mesh, *fec);
+    auto fec                     = field::Field<field::Density>::make_fec<field::Density::Scalar>(2);
+    auto finiteElementSpace      = field::Field<field::Density>::make_fespace<field::Density::Scalar>(mesh, *fec);
 
-    auto otherFec = field::Field<field::Density>::make_fec<field::Density::Scalar>(2);
-    auto otherFiniteElementSpace =
-        field::Field<field::Density>::make_fespace<field::Density::Scalar>(mesh, *otherFec);
+    auto otherFec                = field::Field<field::Density>::make_fec<field::Density::Scalar>(2);
+    auto otherFiniteElementSpace = field::Field<field::Density>::make_fespace<field::Density::Scalar>(mesh, *otherFec);
 
     REQUIRE(finiteElementSpace != nullptr);
     REQUIRE(otherFiniteElementSpace != nullptr);
@@ -959,8 +1010,7 @@ TEST_CASE(
     const mfem::Array<int> empty;
     CHECK_THROWS_AS(
         (field::FieldDofGridFunctionAdapter(
-            field::FieldDofMap(finiteElementSpace->GetTrueVSize() + 1, empty),
-            *finiteElementSpace
+            field::FieldDofMap(finiteElementSpace->GetTrueVSize() + 1, empty), *finiteElementSpace
         )),
         std::invalid_argument
     );

tests/integrators/centrifugal.cpp

@@ -11,7 +11,10 @@ using namespace mean_field;
 namespace {
     struct SerialMappingData {
         explicit SerialMappingData(mfem::Mesh &mesh)
-            : compactification_fes(&mesh, &compactification_fec),
+            : compactification_fes(
+                  &mesh,
+                  &compactification_fec
+              ),
               compactification_coordinate(&compactification_fes),
               mapper(field_dof_test_utils::make_domain_mapper()) {
             compactification_coordinate = 0.0;
@@ -83,7 +86,7 @@ TEST_CASE(
     quadrature::RuleFactory quadrature_factory(std::move(policy));
 
     const quadrature::MappingKind mapping_kind = quadrature::MappingKind::general;
-    const int position_order = displacement_element->GetOrder();
+    const int position_order                   = displacement_element->GetOrder();
 
     quadrature_factory.configure_centrifugal(
         integrator, quadrature::QuadratureRole::discretization, *density_element, *velocity_element, *transformation,
@@ -183,7 +186,7 @@ TEST_CASE(
     quadrature::RuleFactory quadrature_factory(std::move(policy));
 
     const quadrature::MappingKind mapping_kind = quadrature::MappingKind::general;
-    const int position_order = displacement_element->GetOrder();
+    const int position_order                   = displacement_element->GetOrder();
 
     quadrature_factory.configure_centrifugal(
         integrator, quadrature::QuadratureRole::discretization, *density_element, *velocity_element, *transformation,
@@ -344,7 +347,7 @@ TEST_CASE(
     quadrature::RuleFactory quadrature_factory(std::move(policy));
 
     const quadrature::MappingKind mapping_kind = quadrature::MappingKind::general;
-    const int position_order = displacement_element->GetOrder();
+    const int position_order                   = displacement_element->GetOrder();
 
     quadrature_factory.configure_centrifugal(
         integrator, quadrature::QuadratureRole::discretization, *density_element, *velocity_element, *transformation,
@@ -606,8 +609,8 @@ TEST_CASE(
                     mapping_evaluator.GetQuadratureContext(*transformation, integration_point);
                 const double signed_map_determinant = context.detJ;
 
-                local_minimum_map_determinant = std::min(local_minimum_map_determinant, signed_map_determinant);
-                local_maximum_map_determinant = std::max(local_maximum_map_determinant, signed_map_determinant);
+                local_minimum_map_determinant       = std::min(local_minimum_map_determinant, signed_map_determinant);
+                local_maximum_map_determinant       = std::max(local_maximum_map_determinant, signed_map_determinant);
 
                 mapping_evaluator.GetPhysicalPoint(*transformation, integration_point, x_physical);
                 velocity_element->CalcShape(integration_point, velocity_shape);
@@ -808,7 +811,7 @@ TEST_CASE(
                         mapping_evaluator.GetQuadratureContext(*transformation, integration_point);
                     const double signed_map_determinant = context.detJ;
 
-                    local_minimum_determinant = std::min(local_minimum_determinant, signed_map_determinant);
+                    local_minimum_determinant           = std::min(local_minimum_determinant, signed_map_determinant);
 
                     mapping_evaluator.GetPhysicalPoint(*transformation, integration_point, x_physical);
                     velocity_element->CalcShape(integration_point, velocity_shape);
@@ -999,7 +1002,7 @@ TEST_CASE(
                         mapping_evaluator.GetQuadratureContext(*transformation, integration_point);
                     const double signed_map_determinant = context.detJ;
 
-                    local_minimum_determinant = std::min(local_minimum_determinant, signed_map_determinant);
+                    local_minimum_determinant           = std::min(local_minimum_determinant, signed_map_determinant);
 
                     mapping_evaluator.GetPhysicalPoint(*transformation, integration_point, x_physical);
                     velocity_element->CalcShape(integration_point, velocity_shape);

tests/integrators/gravity.cpp

@@ -43,8 +43,8 @@ TEST_CASE(
     mfem::GridFunction displacement(&displacement_fes);
     displacement = 0.0;
     mfem::GridFunction compactification_coordinate(&compactification_fes);
-    compactification_coordinate = 0.0;
-    mapping::DomainMapper domain_mapper = field_dof_test_utils::make_domain_mapper();
+    compactification_coordinate                          = 0.0;
+    mapping::DomainMapper domain_mapper                  = field_dof_test_utils::make_domain_mapper();
 
     const mfem::FiniteElement *velocity_element          = velocity_fes.GetFE(0);
     const mfem::FiniteElement *density_element           = density_fes.GetFE(0);
@@ -129,8 +129,7 @@ TEST_CASE(
     element_residual[displacement_block]      = &displacement_residual;
 
     integrators::GravityMomentumIntegrator integrator(
-        domain_mapper, displacement, compactification_coordinate,
-        integrators::GravityForceJacobianMode::field_coupled
+        domain_mapper, displacement, compactification_coordinate, integrators::GravityForceJacobianMode::field_coupled
     );
 
     const int maximum_order = std::max(
@@ -297,12 +296,10 @@ TEST_CASE(
     mfem::GridFunction displacement(&displacement_fes);
     displacement = 0.0;
     mfem::GridFunction compactification_coordinate(&compactification_fes);
-    compactification_coordinate = 0.0;
+    compactification_coordinate         = 0.0;
     mapping::DomainMapper domain_mapper = field_dof_test_utils::make_domain_mapper();
 
-    mapping::GridFunctionMappingEvaluator mapping_evaluator(
-        domain_mapper, displacement, compactification_coordinate
-    );
+    mapping::GridFunctionMappingEvaluator mapping_evaluator(domain_mapper, displacement, compactification_coordinate);
 
     auto reference_density          = [](const mfem::Vector &x) { return 1.0 + x(0); };
 
@@ -381,8 +378,7 @@ TEST_CASE(
     element_residual[displacement_block]      = &displacement_residual;
 
     integrators::GravityMomentumIntegrator integrator(
-        domain_mapper, displacement, compactification_coordinate,
-        integrators::GravityForceJacobianMode::field_coupled
+        domain_mapper, displacement, compactification_coordinate, integrators::GravityForceJacobianMode::field_coupled
     );
 
     const mfem::IntegrationRule &integration_rule = mfem::IntRules.Get(velocity_element->GetGeomType(), 8);
@@ -471,11 +467,9 @@ TEST_CASE(
     mfem::GridFunction displacement(&displacement_fes);
     displacement = 0.0;
     mfem::GridFunction compactification_coordinate(&compactification_fes);
-    compactification_coordinate = 0.0;
+    compactification_coordinate         = 0.0;
     mapping::DomainMapper domain_mapper = field_dof_test_utils::make_domain_mapper();
-    mapping::GridFunctionMappingEvaluator mapping_evaluator(
-        domain_mapper, displacement, compactification_coordinate
-    );
+    mapping::GridFunctionMappingEvaluator mapping_evaluator(domain_mapper, displacement, compactification_coordinate);
 
     auto radial_gravity = [](const mfem::Vector &x, mfem::Vector &gravity) {
         gravity.SetSize(3);
@@ -553,8 +547,7 @@ TEST_CASE(
     element_residual[displacement_block]      = &displacement_residual;
 
     integrators::GravityMomentumIntegrator integrator(
-        domain_mapper, displacement, compactification_coordinate,
-        integrators::GravityForceJacobianMode::field_coupled
+        domain_mapper, displacement, compactification_coordinate, integrators::GravityForceJacobianMode::field_coupled
     );
 
     const mfem::IntegrationRule &integration_rule = mfem::IntRules.Get(velocity_element->GetGeomType(), 8);

tests/models/stellar_model.cpp

@@ -1,4 +1,6 @@
+#include <array>
 #include <cmath>
+#include <concepts>
 #include <limits>
 #include <memory>
 #include <type_traits>
@@ -12,17 +14,11 @@ import test_helpers;
 namespace {
     struct StellarModelExtensionTracker final {
         int structureValidationCount{0};
-        int surfaceValidationCount{0};
-        int surfaceResolutionCount{0};
 
-        const mean_field::eos::EquationOfState *structureEquationOfState{nullptr};
-
-        const mean_field::eos::EquationOfState *surfaceValidationEquationOfState{nullptr};
-
-        const mean_field::eos::EquationOfState *surfaceResolutionEquationOfState{nullptr};
+        const mean_field::eos::Polytrope *structureEquationOfState{nullptr};
     };
 
-    class StellarModelTestStructure final : public mean_field::models::structure::StructureBase {
+    class StellarModelTestStructure final {
     public:
         explicit StellarModelTestStructure(std::shared_ptr<StellarModelExtensionTracker> tracker)
             : m_tracker(std::move(tracker)),
@@ -32,17 +28,17 @@ namespace {
               ) {
         }
 
-        [[nodiscard]] const mean_field::eos::EquationOfState &equationOfState() const noexcept override {
+        [[nodiscard]] const mean_field::eos::Polytrope &equationOfState() const noexcept {
             m_tracker->structureEquationOfState = &m_equationOfState;
             return m_equationOfState;
         }
 
-        [[nodiscard]] double targetMass() const noexcept override {
+        [[nodiscard]] double targetMass() const noexcept {
             return 2.5;
         }
 
         [[nodiscard]] mean_field::models::structure::StructureSeed
-        makeInitialSeed(const mean_field::models::structure::StructureSeedRequest &request) const override {
+        makeInitialSeed(const mean_field::models::structure::StructureSeedRequest &request) const {
             mean_field::models::structure::StructureSeed seed;
 
             seed.radius.SetSize(2);
@@ -65,7 +61,7 @@ namespace {
             return seed;
         }
 
-        void validate() const override {
+        void validate() const {
             ++m_tracker->structureValidationCount;
         }
 
@@ -74,59 +70,85 @@ namespace {
         mean_field::eos::Polytrope m_equationOfState;
     };
 
-    class StellarModelTestSurface final : public mean_field::surface::SurfaceBase {
+    class StructureWithoutSeed final {
     public:
-        explicit StellarModelTestSurface(std::shared_ptr<StellarModelExtensionTracker> tracker)
-            : m_tracker(std::move(tracker)) {
-        }
+        [[nodiscard]] const mean_field::eos::Polytrope &equationOfState() const noexcept;
 
-        [[nodiscard]]
-        mean_field::surface::ResolvedSurfaceCondition
-        resolve(const mean_field::eos::EquationOfState &equationOfState) const override {
-            ++m_tracker->surfaceResolutionCount;
+        [[nodiscard]] double targetMass() const noexcept;
 
-            m_tracker->surfaceResolutionEquationOfState = &equationOfState;
-
-            return mean_field::surface::ResolvedSurfaceCondition{0.375};
-        }
-
-        void validate(const mean_field::eos::EquationOfState &equationOfState) const override {
-            ++m_tracker->surfaceValidationCount;
-
-            m_tracker->surfaceValidationEquationOfState = &equationOfState;
-        }
-
-    private:
-        std::shared_ptr<StellarModelExtensionTracker> m_tracker;
+        void validate() const;
     };
+
+    class SurfaceWithoutPhysicalQuantity final { };
+
+    struct ModelSurfaceState final {
+        double specificEnthalpy;
+
+        [[nodiscard]] mean_field::eos::SpecificEnthalpyValue
+        value(mean_field::eos::quantity::SpecificEnthalpy) const noexcept {
+            return mean_field::eos::SpecificEnthalpyValue{specificEnthalpy};
+        }
+    };
+
+    using PolytropicStellarModel = mean_field::models::StellarModel<mean_field::models::structure::PolytropicStructure>;
+
+    using ExtensionStellarModel  = mean_field::models::StellarModel<StellarModelTestStructure>;
 } // namespace
 
 TEST_CASE(
     "Stellar Model Owns Structure And Surface Prescriptions",
-    tags::barotrope &tags::unit &tags::model
+    tags::stellar_model_type_contract
 ) {
-    STATIC_REQUIRE_FALSE(std::is_copy_constructible_v<mean_field::models::StellarModel>);
+    STATIC_CHECK(mean_field::models::StructurePrescription<mean_field::models::structure::PolytropicStructure>);
+    STATIC_CHECK(mean_field::models::StructurePrescription<StellarModelTestStructure>);
+    STATIC_CHECK_FALSE(mean_field::models::StructurePrescription<StructureWithoutSeed>);
 
-    STATIC_REQUIRE_FALSE(std::is_copy_assignable_v<mean_field::models::StellarModel>);
+    STATIC_CHECK(
+        mean_field::models::SurfacePrescription<
+            mean_field::surface::ConstantPressureSurface, mean_field::eos::Polytrope>
+    );
+    STATIC_CHECK_FALSE(
+        mean_field::models::SurfacePrescription<SurfaceWithoutPhysicalQuantity, mean_field::eos::Polytrope>
+    );
 
-    STATIC_REQUIRE(std::is_nothrow_move_constructible_v<mean_field::models::StellarModel>);
+    STATIC_CHECK_FALSE(std::derived_from<StellarModelTestStructure, mean_field::models::structure::StructureBase>);
+    STATIC_CHECK_FALSE(
+        std::derived_from<
+            mean_field::models::structure::PolytropicStructure, mean_field::models::structure::StructureBase>
+    );
+    STATIC_CHECK(
+        std::same_as<
+            decltype(std::declval<const mean_field::models::structure::StructureBase &>().equationOfState()),
+            mean_field::eos::EquationOfStateView>
+    );
 
-    STATIC_REQUIRE(std::is_nothrow_move_assignable_v<mean_field::models::StellarModel>);
+    STATIC_REQUIRE_FALSE(std::is_copy_constructible_v<PolytropicStellarModel>);
+
+    STATIC_REQUIRE_FALSE(std::is_copy_assignable_v<PolytropicStellarModel>);
+
+    STATIC_REQUIRE(std::is_nothrow_move_constructible_v<PolytropicStellarModel>);
+
+    STATIC_REQUIRE(std::is_nothrow_move_assignable_v<PolytropicStellarModel>);
 
     mean_field::models::StellarModel model{
         mean_field::models::structure::PolytropicStructure{mean_field::eos::Polytrope{3.0, 0.25}, 1.0},
-        mean_field::surface::Isobaric{0.0}
+        mean_field::surface::ConstantPressureSurface{mean_field::eos::PressureValue{0.0}}
     };
 
-    CHECK(model.targetMass() == 1.0);
-    CHECK(model.resolvedSurfaceCondition().targetEnthalpy == 0.0);
-
-    CHECK(
-        dynamic_cast<const mean_field::models::structure::PolytropicStructure *>(&model.structurePrescription()) !=
-        nullptr
+    STATIC_CHECK(std::same_as<decltype(model), PolytropicStellarModel>);
+    STATIC_CHECK(
+        std::same_as<
+            decltype(model.structurePrescription()), const mean_field::models::structure::PolytropicStructure &>
     );
+    STATIC_CHECK(
+        std::same_as<decltype(model.surfacePrescription()), const mean_field::surface::ConstantPressureSurface &>
+    );
+    STATIC_CHECK(std::same_as<decltype(model.equationOfState()), const mean_field::eos::Polytrope &>);
 
-    CHECK(dynamic_cast<const mean_field::surface::Isobaric *>(&model.surfacePrescription()) != nullptr);
+    CHECK(model.targetMass() == 1.0);
+    CHECK(model.compiledSurfaceConstraint().targetPressure() == mean_field::eos::PressureValue{0.0});
+    CHECK(&model.equationOfState() == &model.structurePrescription().equationOfState());
+    CHECK(model.surfacePrescription().targetPressure() == mean_field::eos::PressureValue{0.0});
 }
 
 TEST_CASE(
@@ -135,7 +157,7 @@ TEST_CASE(
 ) {
     mean_field::models::StellarModel model{
         mean_field::models::structure::PolytropicStructure{mean_field::eos::Polytrope{3.0, 0.25}, 1.0},
-        mean_field::surface::Isobaric{}
+        mean_field::surface::ConstantPressureSurface{mean_field::eos::PressureValue{0.0}}
     };
 
     const mean_field::models::structure::StructureSeed seed =
@@ -153,45 +175,49 @@ TEST_CASE(
 
 TEST_CASE(
     "Moving A Stellar Model Preserves Stable Prescription Addresses",
-    tags::barotrope &tags::unit &tags::model
+    tags::barotrope &tags::unit &tags::model &tags::surface_constraint_lifetime
 ) {
     mean_field::models::StellarModel originalModel{
         mean_field::models::structure::PolytropicStructure{mean_field::eos::Polytrope{3.0, 0.25}, 1.0},
-        mean_field::surface::Isobaric{}
+        mean_field::surface::ConstantPressureSurface{mean_field::eos::PressureValue{0.0}}
     };
 
-    const mean_field::models::structure::StructureBase *structureAddress = &originalModel.structurePrescription();
+    const mean_field::models::structure::PolytropicStructure *structureAddress = &originalModel.structurePrescription();
 
-    const mean_field::surface::SurfaceBase *surfaceAddress               = &originalModel.surfacePrescription();
+    const mean_field::surface::ConstantPressureSurface *surfaceAddress         = &originalModel.surfacePrescription();
 
-    const mean_field::eos::EquationOfState *equationOfStateAddress       = &originalModel.equationOfState();
+    const mean_field::eos::Polytrope *equationOfStateAddress                   = &originalModel.equationOfState();
+
+    const auto *compiledSurfaceConstraintAddress = &originalModel.compiledSurfaceConstraint();
 
     mean_field::models::StellarModel movedModel{std::move(originalModel)};
 
     CHECK(&movedModel.structurePrescription() == structureAddress);
     CHECK(&movedModel.surfacePrescription() == surfaceAddress);
     CHECK(&movedModel.equationOfState() == equationOfStateAddress);
+    CHECK(&movedModel.compiledSurfaceConstraint() == compiledSurfaceConstraintAddress);
     CHECK(movedModel.targetMass() == 1.0);
 }
 
 TEST_CASE(
-    "Stellar Model Resolves A Positive Isobaric Surface",
+    "Stellar Model Compiles A Positive Constant Pressure Surface",
     tags::barotrope &tags::unit &tags::model
 ) {
     constexpr double targetPressure = 0.03125;
 
     mean_field::models::StellarModel model{
         mean_field::models::structure::PolytropicStructure{mean_field::eos::Polytrope{3.0, 0.25}, 1.0},
-        mean_field::surface::Isobaric{targetPressure}
+        mean_field::surface::ConstantPressureSurface{mean_field::eos::PressureValue{targetPressure}}
     };
 
-    const double targetEnthalpy = model.resolvedSurfaceCondition().targetEnthalpy;
+    const double requiredSpecificEnthalpy = mean_field::eos::evaluate<mean_field::eos::quantity::SpecificEnthalpy>(
+                                                model.equationOfState(), mean_field::eos::PressureValue{targetPressure}
+    )
+                                                .value();
 
-    CHECK(targetEnthalpy > 0.0);
-    CHECK(
-        std::abs(model.equationOfState().pressure_from_enthalpy(targetEnthalpy) - targetPressure) <
-        64.0 * std::numeric_limits<double>::epsilon()
-    );
+    CHECK(requiredSpecificEnthalpy > 0.0);
+    CHECK(model.compiledSurfaceConstraint().targetPressure() == mean_field::eos::PressureValue{targetPressure});
+    CHECK(model.compiledSurfaceConstraint().residual(ModelSurfaceState{requiredSpecificEnthalpy}) == 0.0);
 }
 
 TEST_CASE(
@@ -200,27 +226,22 @@ TEST_CASE(
 ) {
     const auto tracker = std::make_shared<StellarModelExtensionTracker>();
 
-    mean_field::models::StellarModel model{StellarModelTestStructure{tracker}, StellarModelTestSurface{tracker}};
+    mean_field::models::StellarModel model{
+        StellarModelTestStructure{tracker},
+        mean_field::surface::ConstantPressureSurface{mean_field::eos::PressureValue{0.375}}
+    };
+
+    STATIC_CHECK(std::same_as<decltype(model), ExtensionStellarModel>);
 
     REQUIRE(tracker->structureValidationCount == 1);
-    REQUIRE(tracker->surfaceValidationCount == 1);
-    REQUIRE(tracker->surfaceResolutionCount == 1);
 
-    CHECK(dynamic_cast<const StellarModelTestStructure *>(&model.structurePrescription()) != nullptr);
-
-    CHECK(dynamic_cast<const StellarModelTestSurface *>(&model.surfacePrescription()) != nullptr);
-
-    const mean_field::eos::EquationOfState *ownedEquationOfState = &model.equationOfState();
+    const mean_field::eos::Polytrope *ownedEquationOfState = &model.equationOfState();
 
     CHECK(tracker->structureEquationOfState == ownedEquationOfState);
 
-    CHECK(tracker->surfaceValidationEquationOfState == ownedEquationOfState);
-
-    CHECK(tracker->surfaceResolutionEquationOfState == ownedEquationOfState);
-
     CHECK(model.targetMass() == 2.5);
 
-    CHECK(model.resolvedSurfaceCondition().targetEnthalpy == 0.375);
+    CHECK(model.compiledSurfaceConstraint().targetPressure() == mean_field::eos::PressureValue{0.375});
 }
 
 TEST_CASE(
@@ -229,23 +250,25 @@ TEST_CASE(
 ) {
     mean_field::models::StellarModel sourceModel{
         mean_field::models::structure::PolytropicStructure{mean_field::eos::Polytrope{3.0, 0.25}, 1.25},
-        mean_field::surface::Isobaric{0.0}
+        mean_field::surface::ConstantPressureSurface{mean_field::eos::PressureValue{0.0}}
     };
 
     mean_field::models::StellarModel destinationModel{
         mean_field::models::structure::PolytropicStructure{mean_field::eos::Polytrope{2.0, 0.5}, 4.0},
-        mean_field::surface::Isobaric{0.02}
+        mean_field::surface::ConstantPressureSurface{mean_field::eos::PressureValue{0.02}}
     };
 
-    const mean_field::models::structure::StructureBase *sourceStructureAddress = &sourceModel.structurePrescription();
+    const mean_field::models::structure::PolytropicStructure *sourceStructureAddress =
+        &sourceModel.structurePrescription();
 
-    const mean_field::surface::SurfaceBase *sourceSurfaceAddress               = &sourceModel.surfacePrescription();
+    const mean_field::surface::ConstantPressureSurface *sourceSurfaceAddress = &sourceModel.surfacePrescription();
 
-    const mean_field::eos::EquationOfState *sourceEquationOfStateAddress       = &sourceModel.equationOfState();
+    const mean_field::eos::Polytrope *sourceEquationOfStateAddress           = &sourceModel.equationOfState();
 
-    const double sourceTargetEnthalpy = sourceModel.resolvedSurfaceCondition().targetEnthalpy;
+    const mean_field::eos::PressureValue sourceTargetPressure =
+        sourceModel.compiledSurfaceConstraint().targetPressure();
 
-    destinationModel                  = std::move(sourceModel);
+    destinationModel = std::move(sourceModel);
 
     CHECK(&destinationModel.structurePrescription() == sourceStructureAddress);
 
@@ -255,5 +278,83 @@ TEST_CASE(
 
     CHECK(destinationModel.targetMass() == 1.25);
 
-    CHECK(destinationModel.resolvedSurfaceCondition().targetEnthalpy == sourceTargetEnthalpy);
+    CHECK(destinationModel.compiledSurfaceConstraint().targetPressure() == sourceTargetPressure);
+}
+
+TEST_CASE(
+    "Stellar Model View Supports Heterogeneous Typed Models",
+    tags::stellar_model_runtime_view
+) {
+    const auto tracker = std::make_shared<StellarModelExtensionTracker>();
+
+    const mean_field::models::StellarModel polytropicModel{
+        mean_field::models::structure::PolytropicStructure{mean_field::eos::Polytrope{3.0, 0.25}, 1.0},
+        mean_field::surface::ConstantPressureSurface{mean_field::eos::PressureValue{0.0}}
+    };
+
+    const mean_field::models::StellarModel extensionModel{
+        StellarModelTestStructure{tracker},
+        mean_field::surface::ConstantPressureSurface{mean_field::eos::PressureValue{0.375}}
+    };
+
+    STATIC_CHECK(std::is_trivially_copyable_v<mean_field::models::StellarModelView>);
+    STATIC_CHECK_FALSE(std::constructible_from<mean_field::models::StellarModelView, PolytropicStellarModel &&>);
+
+    const std::array views{
+        mean_field::models::StellarModelView{polytropicModel}, mean_field::models::StellarModelView{extensionModel}
+    };
+
+    CHECK(views[0].targetMass() == 1.0);
+    CHECK(views[1].targetMass() == 2.5);
+    CHECK(views[1].surfaceCondition().targetPressure == 0.375);
+    REQUIRE(views[1].surfaceDependencies().stateFields.size() == 1);
+    CHECK(
+        views[1].surfaceDependencies().residualRowField ==
+        mean_field::surface::surfaceFieldId<mean_field::field::Enthalpy>
+    );
+
+    const auto pressure =
+        views[0].equationOfState().tryEvaluate<mean_field::eos::quantity::Pressure>(mean_field::eos::DensityValue{0.7});
+
+    REQUIRE(pressure.has_value());
+    CHECK(
+        pressure->value() == mean_field::eos::evaluate<mean_field::eos::quantity::Pressure>(
+                                 polytropicModel.equationOfState(), mean_field::eos::DensityValue{0.7}
+                             )
+                                 .value()
+    );
+
+    const mean_field::models::structure::StructureSeed seed =
+        views[1].makeInitialSeed({.centralDensity = 1.75, .radialSampleCount = 2});
+
+    CHECK(seed.centralDensity == 1.75);
+    CHECK(seed.radius.Size() == 2);
+}
+
+TEST_CASE(
+    "Stellar Model View Retains Stable Pointees When Its Owner Moves",
+    tags::stellar_model_runtime_view
+) {
+    mean_field::models::StellarModel originalModel{
+        mean_field::models::structure::PolytropicStructure{mean_field::eos::Polytrope{3.0, 0.25}, 1.0},
+        mean_field::surface::ConstantPressureSurface{mean_field::eos::PressureValue{0.0}}
+    };
+
+    const mean_field::models::StellarModelView view{originalModel};
+    PolytropicStellarModel movedModel{std::move(originalModel)};
+
+    const auto pressure =
+        view.equationOfState().tryEvaluate<mean_field::eos::quantity::Pressure>(mean_field::eos::DensityValue{0.7});
+    const mean_field::models::structure::StructureSeed seed =
+        view.makeInitialSeed({.centralDensity = 1.0, .radialSampleCount = 8});
+
+    REQUIRE(pressure.has_value());
+    CHECK(view.targetMass() == movedModel.targetMass());
+    CHECK(
+        pressure->value() == mean_field::eos::evaluate<mean_field::eos::quantity::Pressure>(
+                                 movedModel.equationOfState(), mean_field::eos::DensityValue{0.7}
+                             )
+                                 .value()
+    );
+    CHECK(seed.radius.Size() == 8);
 }

tests/operators/contexts/hydrostatic_equilibrium_context.cpp

@@ -164,9 +164,7 @@ TEST_CASE(
     CHECK_FALSE(gravityPotentialReport.updatedDisplacement);
     CHECK_FALSE(gravityPotentialReport.updatedBernoulliConstant);
 
-    CHECK(
-        context.GetBaseGravityPotentialTrue()(context.GetGravityPotentialMap().true_dof(0)) == gravityPotential(0)
-    );
+    CHECK(context.GetBaseGravityPotentialTrue()(context.GetGravityPotentialMap().true_dof(0)) == gravityPotential(0));
 
     ++dependencies.bernoulliConstant.revision;
 

tests/operators/gravity_displacement_force_analytic_comparisons.cpp

@@ -11,386 +11,370 @@ import mean_field;
 import test_helpers;
 
 namespace gravity_displacement_force_analytic_test_utils {
-struct AffineCase {
-  const char *name;
-  std::array<double, 3> scales;
-};
+    struct AffineCase {
+        const char *name;
+        std::array<double, 3> scales;
+    };
 
-[[nodiscard]] double analytic_sphere_volume(const double radius) {
-  return (4.0 / 3.0) * std::numbers::pi * radius * radius * radius;
-}
+    [[nodiscard]] double analytic_sphere_volume(const double radius) {
+        return (4.0 / 3.0) * std::numbers::pi * radius * radius * radius;
+    }
 
-[[nodiscard]] double determinant(const std::array<double, 3> &scales) {
-  return scales[0] * scales[1] * scales[2];
-}
+    [[nodiscard]] double determinant(
+        const std::array<
+            double,
+            3> &scales
+    ) {
+        return scales[0] * scales[1] * scales[2];
+    }
 
-[[nodiscard]] double relative_scalar_error(const double computed,
-                                           const double expected) {
-  return std::abs(computed - expected) / std::max(std::abs(expected), 1.0e-30);
-}
+    [[nodiscard]] double relative_scalar_error(
+        const double computed,
+        const double expected
+    ) {
+        return std::abs(computed - expected) / std::max(std::abs(expected), 1.0e-30);
+    }
 
-[[nodiscard]] mfem::Vector make_constant_density(const mean_field::fem::FEM &f,
-                                                 const double densityValue) {
-  mfem::ParGridFunction densityField(f.densityFes.get());
-  mfem::ConstantCoefficient densityCoefficient(densityValue);
-  densityField.ProjectCoefficient(densityCoefficient);
+    [[nodiscard]] mfem::Vector make_constant_density(
+        const mean_field::fem::FEM &f,
+        const double densityValue
+    ) {
+        mfem::ParGridFunction densityField(f.densityFes.get());
+        mfem::ConstantCoefficient densityCoefficient(densityValue);
+        densityField.ProjectCoefficient(densityCoefficient);
 
-  mfem::Vector densityTrue;
-  densityField.GetTrueDofs(densityTrue);
-  return densityTrue;
-}
+        mfem::Vector densityTrue;
+        densityField.GetTrueDofs(densityTrue);
+        return densityTrue;
+    }
 
-[[nodiscard]] mfem::Vector
-make_reference_gravity(const mean_field::fem::FEM &f,
-                       const std::array<double, 3> &referenceGravity) {
-  mfem::ParGridFunction gravityField(f.gravityFluxFes.get());
+    [[nodiscard]] mfem::Vector make_reference_gravity(
+        const mean_field::fem::FEM &f,
+        const std::array<
+            double,
+            3> &referenceGravity
+    ) {
+        mfem::ParGridFunction gravityField(f.gravityFluxFes.get());
 
-  mfem::VectorFunctionCoefficient gravityCoefficient(
-      f.mesh->Dimension(),
-      [referenceGravity](const mfem::Vector &, mfem::Vector &value) {
-        value.SetSize(3);
+        mfem::VectorFunctionCoefficient gravityCoefficient(
+            f.mesh->Dimension(), [referenceGravity](const mfem::Vector &, mfem::Vector &value) {
+                value.SetSize(3);
 
-        for (int component = 0; component < 3; ++component) {
-          value(component) =
-              referenceGravity[static_cast<std::size_t>(component)];
-        }
-      });
+                for (int component = 0; component < 3; ++component) {
+                    value(component) = referenceGravity[static_cast<std::size_t>(component)];
+                }
+            }
+        );
 
-  gravityField.ProjectCoefficient(gravityCoefficient);
+        gravityField.ProjectCoefficient(gravityCoefficient);
 
-  mfem::Vector gravityTrue;
-  gravityField.GetTrueDofs(gravityTrue);
-  return gravityTrue;
-}
+        mfem::Vector gravityTrue;
+        gravityField.GetTrueDofs(gravityTrue);
+        return gravityTrue;
+    }
 
-[[nodiscard]] mfem::Vector make_radial_gravity(const mean_field::fem::FEM &f,
-                                               const double radialCoefficient) {
-  mfem::ParGridFunction gravityField(f.gravityFluxFes.get());
+    [[nodiscard]] mfem::Vector make_radial_gravity(
+        const mean_field::fem::FEM &f,
+        const double radialCoefficient
+    ) {
+        mfem::ParGridFunction gravityField(f.gravityFluxFes.get());
 
-  mfem::VectorFunctionCoefficient gravityCoefficient(
-      f.mesh->Dimension(),
-      [radialCoefficient](const mfem::Vector &position, mfem::Vector &value) {
-        value.SetSize(position.Size());
+        mfem::VectorFunctionCoefficient gravityCoefficient(
+            f.mesh->Dimension(), [radialCoefficient](const mfem::Vector &position, mfem::Vector &value) {
+                value.SetSize(position.Size());
 
-        for (int component = 0; component < position.Size(); ++component) {
-          value(component) = radialCoefficient * position(component);
-        }
-      });
+                for (int component = 0; component < position.Size(); ++component) {
+                    value(component) = radialCoefficient * position(component);
+                }
+            }
+        );
 
-  gravityField.ProjectCoefficient(gravityCoefficient);
+        gravityField.ProjectCoefficient(gravityCoefficient);
 
-  mfem::Vector gravityTrue;
-  gravityField.GetTrueDofs(gravityTrue);
-  return gravityTrue;
-}
+        mfem::Vector gravityTrue;
+        gravityField.GetTrueDofs(gravityTrue);
+        return gravityTrue;
+    }
 
-[[nodiscard]] mfem::Vector
-make_affine_displacement(const mean_field::fem::FEM &f,
-                         const std::array<double, 3> &scales) {
-  mfem::ParGridFunction displacementField(f.displacementFes.get());
+    [[nodiscard]] mfem::Vector make_affine_displacement(
+        const mean_field::fem::FEM &f,
+        const std::array<
+            double,
+            3> &scales
+    ) {
+        mfem::ParGridFunction displacementField(f.displacementFes.get());
 
-  mfem::VectorFunctionCoefficient displacementCoefficient(
-      f.mesh->Dimension(),
-      [scales](const mfem::Vector &position, mfem::Vector &value) {
-        value.SetSize(position.Size());
+        mfem::VectorFunctionCoefficient displacementCoefficient(
+            f.mesh->Dimension(), [scales](const mfem::Vector &position, mfem::Vector &value) {
+                value.SetSize(position.Size());
 
-        for (int component = 0; component < position.Size(); ++component) {
-          value(component) =
-              (scales[static_cast<std::size_t>(component)] - 1.0) *
-              position(component);
-        }
-      });
+                for (int component = 0; component < position.Size(); ++component) {
+                    value(component) = (scales[static_cast<std::size_t>(component)] - 1.0) * position(component);
+                }
+            }
+        );
 
-  displacementField.ProjectCoefficient(displacementCoefficient);
+        displacementField.ProjectCoefficient(displacementCoefficient);
 
-  mfem::Vector displacementTrue;
-  displacementField.GetTrueDofs(displacementTrue);
-  return displacementTrue;
-}
+        mfem::Vector displacementTrue;
+        displacementField.GetTrueDofs(displacementTrue);
+        return displacementTrue;
+    }
 
-[[nodiscard]] mfem::Vector
-make_constant_test_direction(const mean_field::fem::FEM &f,
-                             const int selectedComponent) {
-  mfem::ParGridFunction testField(f.displacementFes.get());
+    [[nodiscard]] mfem::Vector make_constant_test_direction(
+        const mean_field::fem::FEM &f,
+        const int selectedComponent
+    ) {
+        mfem::ParGridFunction testField(f.displacementFes.get());
 
-  mfem::VectorFunctionCoefficient testCoefficient(
-      f.mesh->Dimension(),
-      [selectedComponent](const mfem::Vector &position, mfem::Vector &value) {
-        value.SetSize(position.Size());
-        value = 0.0;
-        value(selectedComponent) = 1.0;
-      });
+        mfem::VectorFunctionCoefficient testCoefficient(
+            f.mesh->Dimension(), [selectedComponent](const mfem::Vector &position, mfem::Vector &value) {
+                value.SetSize(position.Size());
+                value                    = 0.0;
+                value(selectedComponent) = 1.0;
+            }
+        );
 
-  testField.ProjectCoefficient(testCoefficient);
+        testField.ProjectCoefficient(testCoefficient);
 
-  mfem::Vector testTrue;
-  testField.GetTrueDofs(testTrue);
-  return testTrue;
-}
+        mfem::Vector testTrue;
+        testField.GetTrueDofs(testTrue);
+        return testTrue;
+    }
 
-[[nodiscard]] mfem::Vector
-make_dilation_test_direction(const mean_field::fem::FEM &f) {
-  mfem::ParGridFunction testField(f.displacementFes.get());
+    [[nodiscard]] mfem::Vector make_dilation_test_direction(const mean_field::fem::FEM &f) {
+        mfem::ParGridFunction testField(f.displacementFes.get());
 
-  mfem::VectorFunctionCoefficient testCoefficient(
-      f.mesh->Dimension(), [](const mfem::Vector &position,
-                              mfem::Vector &value) { value = position; });
+        mfem::VectorFunctionCoefficient testCoefficient(
+            f.mesh->Dimension(), [](const mfem::Vector &position, mfem::Vector &value) { value = position; }
+        );
 
-  testField.ProjectCoefficient(testCoefficient);
+        testField.ProjectCoefficient(testCoefficient);
 
-  mfem::Vector testTrue;
-  testField.GetTrueDofs(testTrue);
-  return testTrue;
-}
+        mfem::Vector testTrue;
+        testField.GetTrueDofs(testTrue);
+        return testTrue;
+    }
 
-void set_mass_normalized_density(mean_field::fem::FEM &f,
-                                 const double targetMass,
-                                 mfem::ParGridFunction &densityField) {
-  const mfem::Vector stellarDensityTrue =
-      gravity_prepared_test_utils::make_domain_supported_density(f, true);
+    void set_mass_normalized_density(
+        mean_field::fem::FEM &f,
+        const double targetMass,
+        mfem::ParGridFunction &densityField
+    ) {
+        const mfem::Vector stellarDensityTrue = gravity_prepared_test_utils::make_domain_supported_density(f, true);
 
-  densityField.SetFromTrueDofs(stellarDensityTrue);
+        densityField.SetFromTrueDofs(stellarDensityTrue);
 
-  const double unnormalizedMass =
-      mean_field::analysis::domain_integrate_grid_function(
-          f, densityField, mean_field::utils::DOMAINS::STELLAR);
+        const double unnormalizedMass =
+            mean_field::analysis::domain_integrate_grid_function(f, densityField, mean_field::utils::DOMAINS::STELLAR);
 
-  MFEM_VERIFY(unnormalizedMass > 0.0,
-              "The analytic gravity-force test obtained non-positive mass.");
+        MFEM_VERIFY(unnormalizedMass > 0.0, "The analytic gravity-force test obtained non-positive mass.");
 
-  densityField *= targetMass / unnormalizedMass;
-}
+        densityField *= targetMass / unnormalizedMass;
+    }
 } // namespace gravity_displacement_force_analytic_test_utils
 
-TEST_CASE("Gravity Displacement Force Matches Analytic Affine Resultants",
-          tags::gravity &tags::accuracy &tags::analytic_comparison
-              &tags::integration) {
-  mean_field::utils::Args args = test_utils::setup_args();
+TEST_CASE(
+    "Gravity Displacement Force Matches Analytic Affine Resultants",
+    tags::gravity &tags::accuracy &tags::analytic_comparison &tags::integration
+) {
+    mean_field::utils::Args args = test_utils::setup_args();
 
-  mean_field::fem::FEM f = mean_field::fem::setup_fem(args.mesh_file, args, 0);
+    mean_field::fem::FEM f       = mean_field::fem::setup_fem(args.mesh_file, args, 0);
 
-  REQUIRE(f.okay());
-  REQUIRE(f.domainMapperStateless != nullptr);
-  REQUIRE(f.domainMapperStateless != nullptr);
+    REQUIRE(f.okay());
+    REQUIRE(f.domainMapperStateless != nullptr);
+    REQUIRE(f.domainMapperStateless != nullptr);
 
-  constexpr double densityValue = 1.37;
+    constexpr double densityValue = 1.37;
 
-  constexpr std::array<double, 3> physicalGravity{0.31, -0.47, 0.22};
+    constexpr std::array<double, 3> physicalGravity{0.31, -0.47, 0.22};
 
-  constexpr std::array<
-      gravity_displacement_force_analytic_test_utils::AffineCase, 3>
-      affineCases{{{.name = "identity geometry", .scales = {1.0, 1.0, 1.0}},
-                   {.name = "volume-preserving affine geometry",
-                    .scales = {1.14, 0.93, 1.0 / (1.14 * 0.93)}},
-                   {.name = "volume-changing affine geometry",
-                    .scales = {1.11, 0.96, 1.07}}}};
+    constexpr std::array<gravity_displacement_force_analytic_test_utils::AffineCase, 3> affineCases{
+        {{.name = "identity geometry", .scales = {1.0, 1.0, 1.0}},
+         {.name = "volume-preserving affine geometry", .scales = {1.14, 0.93, 1.0 / (1.14 * 0.93)}},
+         {.name = "volume-changing affine geometry", .scales = {1.11, 0.96, 1.07}}}
+    };
 
-  const mfem::Vector density =
-      gravity_displacement_force_analytic_test_utils::make_constant_density(
-          f, densityValue);
+    const mfem::Vector density = gravity_displacement_force_analytic_test_utils::make_constant_density(f, densityValue);
 
-  const double referenceVolume =
-      gravity_displacement_force_analytic_test_utils::analytic_sphere_volume(
-          mean_field::utils::RADIUS);
+    const double referenceVolume =
+        gravity_displacement_force_analytic_test_utils::analytic_sphere_volume(mean_field::utils::RADIUS);
 
-  constexpr double relativeTolerance = 5.0e-6;
+    constexpr double relativeTolerance = 5.0e-6;
 
-  for (const gravity_displacement_force_analytic_test_utils::AffineCase
-           &affineCase : affineCases) {
-    DYNAMIC_SECTION(affineCase.name) {
-      const double mapDeterminant =
-          gravity_displacement_force_analytic_test_utils::determinant(
-              affineCase.scales);
+    for (const gravity_displacement_force_analytic_test_utils::AffineCase &affineCase : affineCases) {
+        DYNAMIC_SECTION(affineCase.name) {
+            const double mapDeterminant =
+                gravity_displacement_force_analytic_test_utils::determinant(affineCase.scales);
 
-      REQUIRE(mapDeterminant > 0.0);
+            REQUIRE(mapDeterminant > 0.0);
 
-      std::array<double, 3> referenceGravity{};
+            std::array<double, 3> referenceGravity{};
 
-      /*
-       * For x = A X, the H(div) Piola relation is
-       *
-       *     g_phys = A g_ref / det(A).
-       *
-       * Prescribe the RT pullback that represents the requested
-       * constant physical gravity field exactly.
-       */
-      for (int component = 0; component < 3; ++component) {
-        referenceGravity[static_cast<std::size_t>(component)] =
-            mapDeterminant *
-            physicalGravity[static_cast<std::size_t>(component)] /
-            affineCase.scales[static_cast<std::size_t>(component)];
-      }
+            /*
+             * For x = A X, the H(div) Piola relation is
+             *
+             *     g_phys = A g_ref / det(A).
+             *
+             * Prescribe the RT pullback that represents the requested
+             * constant physical gravity field exactly.
+             */
+            for (int component = 0; component < 3; ++component) {
+                referenceGravity[static_cast<std::size_t>(component)] =
+                    mapDeterminant * physicalGravity[static_cast<std::size_t>(component)] /
+                    affineCase.scales[static_cast<std::size_t>(component)];
+            }
 
-      const mfem::Vector gravityGradient =
-          gravity_displacement_force_analytic_test_utils::
-              make_reference_gravity(f, referenceGravity);
+            const mfem::Vector gravityGradient =
+                gravity_displacement_force_analytic_test_utils::make_reference_gravity(f, referenceGravity);
 
-      const mfem::Vector displacement =
-          gravity_displacement_force_analytic_test_utils::
-              make_affine_displacement(f, affineCase.scales);
+            const mfem::Vector displacement =
+                gravity_displacement_force_analytic_test_utils::make_affine_displacement(f, affineCase.scales);
 
-      mfem::Vector residual;
+            mfem::Vector residual;
 
-      mean_field::operators::kernels::apply_gravity_displacement_force_residual(
-          f, *f.domainMapperStateless, density, gravityGradient, displacement,
-          residual);
+            mean_field::operators::kernels::apply_gravity_displacement_force_residual(
+                f, *f.domainMapperStateless, density, gravityGradient, displacement, residual
+            );
 
-      for (int component = 0; component < 3; ++component) {
-        const mfem::Vector testDirection =
-            gravity_displacement_force_analytic_test_utils::
-                make_constant_test_direction(f, component);
+            for (int component = 0; component < 3; ++component) {
+                const mfem::Vector testDirection =
+                    gravity_displacement_force_analytic_test_utils::make_constant_test_direction(f, component);
 
-        const double computedResultant =
-            gravity_prepared_test_utils::global_dot(residual, testDirection,
-                                                    f.mesh->GetComm());
+                const double computedResultant =
+                    gravity_prepared_test_utils::global_dot(residual, testDirection, f.mesh->GetComm());
 
-        const double expectedResultant =
-            densityValue *
-            physicalGravity[static_cast<std::size_t>(component)] *
-            mapDeterminant * referenceVolume;
+                const double expectedResultant = densityValue * physicalGravity[static_cast<std::size_t>(component)] *
+                                                 mapDeterminant * referenceVolume;
 
-        const double relativeError =
-            gravity_displacement_force_analytic_test_utils::
-                relative_scalar_error(computedResultant, expectedResultant);
+                const double relativeError     = gravity_displacement_force_analytic_test_utils::relative_scalar_error(
+                    computedResultant, expectedResultant
+                );
 
-        CAPTURE(component);
-        INFO("Map determinant = " << mapDeterminant);
-        INFO("Computed resultant = " << computedResultant);
-        INFO("Analytic resultant = " << expectedResultant);
-        INFO("Relative resultant error = " << relativeError);
+                CAPTURE(component);
+                INFO("Map determinant = " << mapDeterminant);
+                INFO("Computed resultant = " << computedResultant);
+                INFO("Analytic resultant = " << expectedResultant);
+                INFO("Relative resultant error = " << relativeError);
 
-        CHECK(relativeError < relativeTolerance);
-      }
+                CHECK(relativeError < relativeTolerance);
+            }
+        }
     }
-  }
 }
 
 TEST_CASE(
     "Gravity Displacement Force Reproduces Analytic Homogeneous Sphere Work",
-    tags::gravity &tags::accuracy &tags::analytic_comparison
-        &tags::integration) {
-  mean_field::utils::Args args = test_utils::setup_args();
+    tags::gravity &tags::accuracy &tags::analytic_comparison &tags::integration
+) {
+    mean_field::utils::Args args = test_utils::setup_args();
 
-  mean_field::fem::FEM f = mean_field::fem::setup_fem(args.mesh_file, args, 0);
+    mean_field::fem::FEM f       = mean_field::fem::setup_fem(args.mesh_file, args, 0);
 
-  REQUIRE(f.okay());
-  REQUIRE(f.domainMapperStateless != nullptr);
+    REQUIRE(f.okay());
+    REQUIRE(f.domainMapperStateless != nullptr);
 
-  const double radius = mean_field::utils::RADIUS;
-  const double mass = mean_field::utils::MASS;
-  const double volume =
-      gravity_displacement_force_analytic_test_utils::analytic_sphere_volume(
-          radius);
+    const double radius       = mean_field::utils::RADIUS;
+    const double mass         = mean_field::utils::MASS;
+    const double volume       = gravity_displacement_force_analytic_test_utils::analytic_sphere_volume(radius);
 
-  const double densityValue = mass / volume;
-  const double radialGravityCoefficient =
-      mean_field::utils::G * mass / (radius * radius * radius);
+    const double densityValue = mass / volume;
+    const double radialGravityCoefficient = mean_field::utils::G * mass / (radius * radius * radius);
 
-  const mfem::Vector density =
-      gravity_displacement_force_analytic_test_utils::make_constant_density(
-          f, densityValue);
+    const mfem::Vector density = gravity_displacement_force_analytic_test_utils::make_constant_density(f, densityValue);
 
-  const mfem::Vector gravityGradient =
-      gravity_displacement_force_analytic_test_utils::make_radial_gravity(
-          f, radialGravityCoefficient);
+    const mfem::Vector gravityGradient =
+        gravity_displacement_force_analytic_test_utils::make_radial_gravity(f, radialGravityCoefficient);
 
-  mfem::Vector displacement(f.displacementFes->GetTrueVSize());
-  displacement = 0.0;
+    mfem::Vector displacement(f.displacementFes->GetTrueVSize());
+    displacement = 0.0;
 
-  mfem::Vector residual;
+    mfem::Vector residual;
 
-  mean_field::operators::kernels::apply_gravity_displacement_force_residual(
-      f, *f.domainMapperStateless, density, gravityGradient, displacement,
-      residual);
+    mean_field::operators::kernels::apply_gravity_displacement_force_residual(
+        f, *f.domainMapperStateless, density, gravityGradient, displacement, residual
+    );
 
-  const mfem::Vector dilationDirection =
-      gravity_displacement_force_analytic_test_utils::
-          make_dilation_test_direction(f);
+    const mfem::Vector dilationDirection =
+        gravity_displacement_force_analytic_test_utils::make_dilation_test_direction(f);
 
-  const double computedWork = gravity_prepared_test_utils::global_dot(
-      residual, dilationDirection, f.mesh->GetComm());
+    const double computedWork = gravity_prepared_test_utils::global_dot(residual, dilationDirection, f.mesh->GetComm());
 
-  const double analyticWork =
-      (3.0 / 5.0) * mean_field::utils::G * mass * mass / radius;
+    const double analyticWork = (3.0 / 5.0) * mean_field::utils::G * mass * mass / radius;
 
-  const double relativeError =
-      gravity_displacement_force_analytic_test_utils::relative_scalar_error(
-          computedWork, analyticWork);
+    const double relativeError =
+        gravity_displacement_force_analytic_test_utils::relative_scalar_error(computedWork, analyticWork);
 
-  INFO("Computed positive gravity work = " << computedWork);
-  INFO("Analytic positive gravity work = " << analyticWork);
-  INFO("Computed gravitational virial = " << -computedWork);
-  INFO("Analytic binding energy = " << -analyticWork);
-  INFO("Relative analytic work error = " << relativeError);
+    INFO("Computed positive gravity work = " << computedWork);
+    INFO("Analytic positive gravity work = " << analyticWork);
+    INFO("Computed gravitational virial = " << -computedWork);
+    INFO("Analytic binding energy = " << -analyticWork);
+    INFO("Relative analytic work error = " << relativeError);
 
-  REQUIRE(computedWork > 0.0);
-  CHECK(relativeError < 1.0e-5);
+    REQUIRE(computedWork > 0.0);
+    CHECK(relativeError < 1.0e-5);
 }
 
-TEST_CASE("Solved Homogeneous Sphere Gravity Force Matches Analytic Virial",
-          tags::gravity &tags::accuracy &tags::analytic_comparison
-              &tags::integration &tags::initialization) {
-  mean_field::utils::Args args = test_utils::setup_args();
-  args.p.rtol = 1.0e-13;
-  args.p.max_iters = std::max(args.p.max_iters, 1000);
+TEST_CASE(
+    "Solved Homogeneous Sphere Gravity Force Matches Analytic Virial",
+    tags::gravity &tags::accuracy &tags::analytic_comparison &tags::integration &tags::initialization
+) {
+    mean_field::utils::Args args = test_utils::setup_args();
+    args.p.rtol                  = 1.0e-13;
+    args.p.max_iters             = std::max(args.p.max_iters, 1000);
 
-  mean_field::fem::FEM f = mean_field::fem::setup_fem(args.mesh_file, args, 0);
+    mean_field::fem::FEM f       = mean_field::fem::setup_fem(args.mesh_file, args, 0);
 
-  REQUIRE(f.okay());
-  REQUIRE(f.domainMapperStateless != nullptr);
+    REQUIRE(f.okay());
+    REQUIRE(f.domainMapperStateless != nullptr);
 
-  mfem::ParGridFunction displacementField(f.displacementFes.get());
-  displacementField = 0.0;
+    mfem::ParGridFunction displacementField(f.displacementFes.get());
+    displacementField = 0.0;
 
-  REQUIRE(f.domainMapperStateless != nullptr);
-  *f.displacement = 0.0;
+    REQUIRE(f.domainMapperStateless != nullptr);
+    *f.displacement     = 0.0;
 
-  const double radius = mean_field::utils::RADIUS;
-  const double mass = mean_field::utils::MASS;
+    const double radius = mean_field::utils::RADIUS;
+    const double mass   = mean_field::utils::MASS;
 
-  mfem::ParGridFunction densityField(f.densityFes.get());
+    mfem::ParGridFunction densityField(f.densityFes.get());
 
-  gravity_displacement_force_analytic_test_utils::set_mass_normalized_density(
-      f, mass, densityField);
+    gravity_displacement_force_analytic_test_utils::set_mass_normalized_density(f, mass, densityField);
 
-  const mean_field::physics::GravitySolution gravitySolution =
-      mean_field::physics::solve_gravity_field(f, args, densityField,
-                                               displacementField);
+    const mean_field::physics::GravitySolution gravitySolution =
+        mean_field::physics::solve_gravity_field(f, args, densityField, displacementField);
 
-  mfem::Vector densityTrue;
-  mfem::Vector gravityGradientTrue;
-  mfem::Vector displacementTrue;
+    mfem::Vector densityTrue;
+    mfem::Vector gravityGradientTrue;
+    mfem::Vector displacementTrue;
 
-  densityField.GetTrueDofs(densityTrue);
-  gravitySolution.gradPhi.GetTrueDofs(gravityGradientTrue);
-  displacementField.GetTrueDofs(displacementTrue);
+    densityField.GetTrueDofs(densityTrue);
+    gravitySolution.gradPhi.GetTrueDofs(gravityGradientTrue);
+    displacementField.GetTrueDofs(displacementTrue);
 
-  mfem::Vector residual;
+    mfem::Vector residual;
 
-  mean_field::operators::kernels::apply_gravity_displacement_force_residual(
-      f, *f.domainMapperStateless, densityTrue, gravityGradientTrue,
-      displacementTrue, residual);
+    mean_field::operators::kernels::apply_gravity_displacement_force_residual(
+        f, *f.domainMapperStateless, densityTrue, gravityGradientTrue, displacementTrue, residual
+    );
 
-  const mfem::Vector dilationDirection =
-      gravity_displacement_force_analytic_test_utils::
-          make_dilation_test_direction(f);
+    const mfem::Vector dilationDirection =
+        gravity_displacement_force_analytic_test_utils::make_dilation_test_direction(f);
 
-  const double computedWork = gravity_prepared_test_utils::global_dot(
-      residual, dilationDirection, f.mesh->GetComm());
+    const double computedWork = gravity_prepared_test_utils::global_dot(residual, dilationDirection, f.mesh->GetComm());
 
-  const double analyticWork =
-      (3.0 / 5.0) * mean_field::utils::G * mass * mass / radius;
+    const double analyticWork = (3.0 / 5.0) * mean_field::utils::G * mass * mass / radius;
 
-  const double relativeError =
-      gravity_displacement_force_analytic_test_utils::relative_scalar_error(
-          computedWork, analyticWork);
+    const double relativeError =
+        gravity_displacement_force_analytic_test_utils::relative_scalar_error(computedWork, analyticWork);
 
-  INFO("Solved-field positive gravity work = " << computedWork);
-  INFO("Analytic positive gravity work = " << analyticWork);
-  INFO("Solved-field gravitational virial = " << -computedWork);
-  INFO("Analytic homogeneous-sphere binding energy = " << -analyticWork);
-  INFO("Relative solved-field virial error = " << relativeError);
+    INFO("Solved-field positive gravity work = " << computedWork);
+    INFO("Analytic positive gravity work = " << analyticWork);
+    INFO("Solved-field gravitational virial = " << -computedWork);
+    INFO("Analytic homogeneous-sphere binding energy = " << -analyticWork);
+    INFO("Relative solved-field virial error = " << relativeError);
 
-  REQUIRE(computedWork > 0.0);
-  CHECK(relativeError < 1.0e-5);
+    REQUIRE(computedWork > 0.0);
+    CHECK(relativeError < 1.0e-5);
 }

tests/operators/kernels/barotropic_closure_kernels.cpp

@@ -72,7 +72,10 @@ TEST_CASE(
 
     constexpr double enthalpyValue  = 0.8;
 
-    const double densityValue       = barotrope.density_from_enthalpy(enthalpyValue);
+    const double densityValue       = mean_field::eos::evaluate<mean_field::eos::quantity::Density>(
+                                          barotrope, mean_field::eos::SpecificEnthalpyValue{enthalpyValue}
+    )
+                                          .value();
 
     const mfem::Vector enthalpy     = project_constant(*f.enthalpyFes, enthalpyValue);
 

tests/operators/prepared_barotropic_closure.cpp

@@ -242,8 +242,12 @@ namespace prepared_barotropic_closure_test_utils {
         const ClosureCondition &condition
     ) {
         mfem::FunctionCoefficient coefficient([&equationOfState, condition](const mfem::Vector &position) {
-            const double enthalpy = evaluate_enthalpy(position, condition);
-            return condition.densityFactor * equationOfState.density_from_enthalpy(enthalpy) + condition.densityOffset +
+            const double enthalpy               = evaluate_enthalpy(position, condition);
+            const double equationOfStateDensity = mean_field::eos::evaluate<mean_field::eos::quantity::Density>(
+                                                      equationOfState, mean_field::eos::SpecificEnthalpyValue{enthalpy}
+            )
+                                                      .value();
+            return condition.densityFactor * equationOfStateDensity + condition.densityOffset +
                    condition.densityGradient * (0.40 * position(0) + 0.25 * position(1) - 0.15 * position(2));
         });
         return project_scalar(*f.densityFes, coefficient);
@@ -784,8 +788,12 @@ namespace prepared_barotropic_closure_test_utils {
         const Maps maps(f);
         const mean_field::eos::Polytrope equationOfState(3.0, 1.5);
 
-        constexpr double enthalpyValue       = 1.20;
-        const double equilibriumDensityValue = equationOfState.density_from_enthalpy(enthalpyValue);
+        constexpr double enthalpyValue = 1.20;
+        const double equilibriumDensityValue =
+            mean_field::eos::evaluate<mean_field::eos::quantity::Density>(
+                equationOfState, mean_field::eos::SpecificEnthalpyValue{enthalpyValue}
+            )
+                .value();
 
         const mfem::Vector enthalpy = reduce(maps.enthalpy, make_constant_field(*f.enthalpyFes, enthalpyValue));
         const mfem::Vector equilibriumDensity =

tests/operators/prepared_hdiv_mass.cpp

@@ -10,181 +10,157 @@ using namespace mean_field;
 using Catch::Matchers::WithinAbs;
 namespace prepared_test = gravity_prepared_test_utils;
 
-TEST_CASE("Prepared Mapped Hdiv Mass Matches Stateless Kernel",
-          tags::gravity_prepared) {
-  auto args = test_utils::setup_args();
-  fem::FEM f = fem::setup_fem(args.mesh_file, args, 0);
+TEST_CASE(
+    "Prepared Mapped Hdiv Mass Matches Stateless Kernel",
+    tags::gravity_prepared
+) {
+    auto args  = test_utils::setup_args();
+    fem::FEM f = fem::setup_fem(args.mesh_file, args, 0);
 
-  operators::PreparedMappedHDivMassOperator prepared_operator(
-      f, *f.domainMapperStateless);
-  REQUIRE(prepared_operator.Width() ==
-          prepared_operator.GetFluxMap().reduced_size());
-  REQUIRE(prepared_operator.Height() ==
-          prepared_operator.GetFluxMap().reduced_size());
+    operators::PreparedMappedHDivMassOperator prepared_operator(f, *f.domainMapperStateless);
+    REQUIRE(prepared_operator.Width() == prepared_operator.GetFluxMap().reduced_size());
+    REQUIRE(prepared_operator.Height() == prepared_operator.GetFluxMap().reduced_size());
 
-  const mfem::Vector gravity_gradient_true =
-      prepared_test::make_deterministic_vector(f.gravityFluxFes->GetTrueVSize(),
-                                               0.21);
-  const mfem::Vector gravity_gradient =
-      prepared_operator.GetFluxMap().gather(gravity_gradient_true);
-  const MPI_Comm communicator = f.gravityFluxFes->GetComm();
+    const mfem::Vector gravity_gradient_true =
+        prepared_test::make_deterministic_vector(f.gravityFluxFes->GetTrueVSize(), 0.21);
+    const mfem::Vector gravity_gradient = prepared_operator.GetFluxMap().gather(gravity_gradient_true);
+    const MPI_Comm communicator         = f.gravityFluxFes->GetComm();
 
-  mfem::Vector identity_action;
-  mfem::Vector deformed_action;
+    mfem::Vector identity_action;
+    mfem::Vector deformed_action;
 
-  for (const double deformation_scale : {0.0, 1.0}) {
-    const mfem::Vector displacement_true =
-        prepared_test::make_displacement(f, deformation_scale);
+    for (const double deformation_scale : {0.0, 1.0}) {
+        const mfem::Vector displacement_true = prepared_test::make_displacement(f, deformation_scale);
+        const mfem::Vector displacement      = prepared_operator.GetDisplacementMap().gather(displacement_true);
+
+        prepared_operator.Prepare(displacement);
+
+        mfem::Vector prepared_action;
+
+        prepared_operator.Mult(gravity_gradient, prepared_action);
+        mfem::Vector reference_action_true;
+        operators::kernels::apply_mapped_hdiv_mass(
+            f, *f.domainMapperStateless, gravity_gradient_true, displacement_true, reference_action_true
+        );
+        const mfem::Vector reference_action = prepared_operator.GetFluxMap().gather(reference_action_true);
+
+        const double relative_error = prepared_test::relative_error(prepared_action, reference_action, communicator);
+
+        INFO("Deformation scale = " << deformation_scale);
+        INFO("Prepared action norm = " << prepared_test::global_norm(prepared_action, communicator));
+        INFO("Reference action norm = " << prepared_test::global_norm(reference_action, communicator));
+        INFO("Relative prepared-operator error = " << relative_error);
+
+        REQUIRE(prepared_operator.IsPrepared());
+        CHECK_THAT(relative_error, WithinAbs(0.0, 2.0e-11));
+
+        if (deformation_scale == 0.0) {
+            identity_action = prepared_action;
+        } else {
+            deformed_action = prepared_action;
+        }
+    }
+
+    const double geometry_change = prepared_test::relative_error(deformed_action, identity_action, communicator);
+
+    INFO("Relative action change under deformation = " << geometry_change);
+
+    CHECK(prepared_operator.GetPreparationCount() == 2);
+    CHECK(geometry_change > 1.0e-5);
+}
+
+TEST_CASE(
+    "Prepared Mapped Hdiv Mass Preserves Operator Identities",
+    tags::gravity_prepared
+) {
+    auto args  = test_utils::setup_args();
+    fem::FEM f = fem::setup_fem(args.mesh_file, args, 0);
+
+    operators::PreparedMappedHDivMassOperator prepared_operator(f, *f.domainMapperStateless);
+    REQUIRE(prepared_operator.Width() == prepared_operator.GetFluxMap().reduced_size());
+    REQUIRE(prepared_operator.Height() == prepared_operator.GetFluxMap().reduced_size());
     const mfem::Vector displacement =
-        prepared_operator.GetDisplacementMap().gather(displacement_true);
-
+        prepared_operator.GetDisplacementMap().gather(prepared_test::make_displacement(f, 1.0));
     prepared_operator.Prepare(displacement);
 
-    mfem::Vector prepared_action;
+    const mfem::Vector first = prepared_operator.GetFluxMap().gather(
+        prepared_test::make_deterministic_vector(f.gravityFluxFes->GetTrueVSize(), 0.17)
+    );
+    const mfem::Vector second = prepared_operator.GetFluxMap().gather(
+        prepared_test::make_deterministic_vector(f.gravityFluxFes->GetTrueVSize(), 0.83)
+    );
+    const mfem::Vector combination = prepared_test::linear_combination(first, 1.7, second, -0.4);
 
-    prepared_operator.Mult(gravity_gradient, prepared_action);
-    mfem::Vector reference_action_true;
-    operators::kernels::apply_mapped_hdiv_mass(
-        f, *f.domainMapperStateless, gravity_gradient_true, displacement_true,
-        reference_action_true);
-    const mfem::Vector reference_action =
-        prepared_operator.GetFluxMap().gather(reference_action_true);
+    mfem::Vector first_action;
+    mfem::Vector second_action;
+    mfem::Vector combination_action;
+    mfem::Vector zero_action;
 
-    const double relative_error = prepared_test::relative_error(
-        prepared_action, reference_action, communicator);
+    prepared_operator.Mult(first, first_action);
+    prepared_operator.Mult(second, second_action);
+    prepared_operator.Mult(combination, combination_action);
 
-    INFO("Deformation scale = " << deformation_scale);
-    INFO("Prepared action norm = "
-         << prepared_test::global_norm(prepared_action, communicator));
-    INFO("Reference action norm = "
-         << prepared_test::global_norm(reference_action, communicator));
-    INFO("Relative prepared-operator error = " << relative_error);
+    mfem::Vector expected_combination = prepared_test::linear_combination(first_action, 1.7, second_action, -0.4);
 
-    REQUIRE(prepared_operator.IsPrepared());
-    CHECK_THAT(relative_error, WithinAbs(0.0, 2.0e-11));
+    mfem::Vector zero(first.Size());
+    zero = 0.0;
+    prepared_operator.Mult(zero, zero_action);
 
-    if (deformation_scale == 0.0) {
-      identity_action = prepared_action;
-    } else {
-      deformed_action = prepared_action;
+    const MPI_Comm communicator       = f.gravityFluxFes->GetComm();
+
+    const double first_second_product = prepared_test::global_dot(first, second_action, communicator);
+    const double second_first_product = prepared_test::global_dot(second, first_action, communicator);
+    const double symmetry_error = prepared_test::relative_scalar_error(first_second_product, second_first_product);
+    const double linearity_error =
+        prepared_test::relative_error(combination_action, expected_combination, communicator);
+    const double first_energy             = prepared_test::global_dot(first, first_action, communicator);
+    const double second_energy            = prepared_test::global_dot(second, second_action, communicator);
+    const std::uint64_t preparation_count = prepared_operator.GetPreparationCount();
+
+    mfem::Vector repeated_action;
+    prepared_operator.Mult(first, repeated_action);
+
+    INFO("u^T M v = " << first_second_product);
+    INFO("v^T M u = " << second_first_product);
+    INFO("Relative symmetry error = " << symmetry_error);
+    INFO("Relative linearity error = " << linearity_error);
+    INFO("u^T M u = " << first_energy);
+    INFO("v^T M v = " << second_energy);
+
+    CHECK_THAT(symmetry_error, WithinAbs(0.0, 2.0e-12));
+    CHECK_THAT(linearity_error, WithinAbs(0.0, 2.0e-12));
+    CHECK_THAT(prepared_test::global_norm(zero_action, communicator), WithinAbs(0.0, 1.0e-14));
+    CHECK(first_energy > 0.0);
+    CHECK(second_energy > 0.0);
+    CHECK(prepared_test::relative_error(repeated_action, first_action, communicator) < 2.0e-14);
+    CHECK(prepared_operator.GetPreparationCount() == preparation_count);
+}
+
+TEST_CASE(
+    "Prepared Mapped Hdiv Mass Diagonal Is Positive Across Both Domains",
+    tags::gravity_prepared
+) {
+    auto args  = test_utils::setup_args();
+    fem::FEM f = fem::setup_fem(args.mesh_file, args, 0);
+
+    operators::PreparedMappedHDivMassOperator prepared_operator(f, *f.domainMapperStateless);
+    const mfem::Vector displacement =
+        prepared_operator.GetDisplacementMap().gather(prepared_test::make_displacement(f, 1.0));
+    prepared_operator.Prepare(displacement);
+
+    mfem::Vector diagonal;
+    mfem::Vector true_diagonal;
+    prepared_operator.AssembleDiagonal(diagonal);
+    prepared_operator.AssembleTrueDiagonal(true_diagonal);
+
+    REQUIRE(diagonal.Size() == prepared_operator.Height());
+    REQUIRE(true_diagonal.Size() == prepared_operator.GetFluxMap().full_size());
+
+    const mfem::Vector gathered_true_diagonal = prepared_operator.GetFluxMap().gather(true_diagonal);
+
+    for (int i = 0; i < diagonal.Size(); ++i) {
+        REQUIRE(std::isfinite(diagonal(i)));
+        CHECK(diagonal(i) > 0.0);
+        CHECK_THAT(diagonal(i), WithinAbs(gathered_true_diagonal(i), 1.0e-14 * std::abs(diagonal(i))));
     }
-  }
-
-  const double geometry_change = prepared_test::relative_error(
-      deformed_action, identity_action, communicator);
-
-  INFO("Relative action change under deformation = " << geometry_change);
-
-  CHECK(prepared_operator.GetPreparationCount() == 2);
-  CHECK(geometry_change > 1.0e-5);
-}
-
-TEST_CASE("Prepared Mapped Hdiv Mass Preserves Operator Identities",
-          tags::gravity_prepared) {
-  auto args = test_utils::setup_args();
-  fem::FEM f = fem::setup_fem(args.mesh_file, args, 0);
-
-  operators::PreparedMappedHDivMassOperator prepared_operator(
-      f, *f.domainMapperStateless);
-  REQUIRE(prepared_operator.Width() ==
-          prepared_operator.GetFluxMap().reduced_size());
-  REQUIRE(prepared_operator.Height() ==
-          prepared_operator.GetFluxMap().reduced_size());
-  const mfem::Vector displacement =
-      prepared_operator.GetDisplacementMap().gather(
-          prepared_test::make_displacement(f, 1.0));
-  prepared_operator.Prepare(displacement);
-
-  const mfem::Vector first = prepared_operator.GetFluxMap().gather(
-      prepared_test::make_deterministic_vector(f.gravityFluxFes->GetTrueVSize(),
-                                               0.17));
-  const mfem::Vector second = prepared_operator.GetFluxMap().gather(
-      prepared_test::make_deterministic_vector(f.gravityFluxFes->GetTrueVSize(),
-                                               0.83));
-  const mfem::Vector combination =
-      prepared_test::linear_combination(first, 1.7, second, -0.4);
-
-  mfem::Vector first_action;
-  mfem::Vector second_action;
-  mfem::Vector combination_action;
-  mfem::Vector zero_action;
-
-  prepared_operator.Mult(first, first_action);
-  prepared_operator.Mult(second, second_action);
-  prepared_operator.Mult(combination, combination_action);
-
-  mfem::Vector expected_combination =
-      prepared_test::linear_combination(first_action, 1.7, second_action, -0.4);
-
-  mfem::Vector zero(first.Size());
-  zero = 0.0;
-  prepared_operator.Mult(zero, zero_action);
-
-  const MPI_Comm communicator = f.gravityFluxFes->GetComm();
-
-  const double first_second_product =
-      prepared_test::global_dot(first, second_action, communicator);
-  const double second_first_product =
-      prepared_test::global_dot(second, first_action, communicator);
-  const double symmetry_error = prepared_test::relative_scalar_error(
-      first_second_product, second_first_product);
-  const double linearity_error = prepared_test::relative_error(
-      combination_action, expected_combination, communicator);
-  const double first_energy =
-      prepared_test::global_dot(first, first_action, communicator);
-  const double second_energy =
-      prepared_test::global_dot(second, second_action, communicator);
-  const std::uint64_t preparation_count =
-      prepared_operator.GetPreparationCount();
-
-  mfem::Vector repeated_action;
-  prepared_operator.Mult(first, repeated_action);
-
-  INFO("u^T M v = " << first_second_product);
-  INFO("v^T M u = " << second_first_product);
-  INFO("Relative symmetry error = " << symmetry_error);
-  INFO("Relative linearity error = " << linearity_error);
-  INFO("u^T M u = " << first_energy);
-  INFO("v^T M v = " << second_energy);
-
-  CHECK_THAT(symmetry_error, WithinAbs(0.0, 2.0e-12));
-  CHECK_THAT(linearity_error, WithinAbs(0.0, 2.0e-12));
-  CHECK_THAT(prepared_test::global_norm(zero_action, communicator),
-             WithinAbs(0.0, 1.0e-14));
-  CHECK(first_energy > 0.0);
-  CHECK(second_energy > 0.0);
-  CHECK(prepared_test::relative_error(repeated_action, first_action,
-                                      communicator) < 2.0e-14);
-  CHECK(prepared_operator.GetPreparationCount() == preparation_count);
-}
-
-TEST_CASE("Prepared Mapped Hdiv Mass Diagonal Is Positive Across Both Domains",
-          tags::gravity_prepared) {
-  auto args = test_utils::setup_args();
-  fem::FEM f = fem::setup_fem(args.mesh_file, args, 0);
-
-  operators::PreparedMappedHDivMassOperator prepared_operator(
-      f, *f.domainMapperStateless);
-  const mfem::Vector displacement =
-      prepared_operator.GetDisplacementMap().gather(
-          prepared_test::make_displacement(f, 1.0));
-  prepared_operator.Prepare(displacement);
-
-  mfem::Vector diagonal;
-  mfem::Vector true_diagonal;
-  prepared_operator.AssembleDiagonal(diagonal);
-  prepared_operator.AssembleTrueDiagonal(true_diagonal);
-
-  REQUIRE(diagonal.Size() == prepared_operator.Height());
-  REQUIRE(true_diagonal.Size() == prepared_operator.GetFluxMap().full_size());
-
-  const mfem::Vector gathered_true_diagonal =
-      prepared_operator.GetFluxMap().gather(true_diagonal);
-
-  for (int i = 0; i < diagonal.Size(); ++i) {
-    REQUIRE(std::isfinite(diagonal(i)));
-    CHECK(diagonal(i) > 0.0);
-    CHECK_THAT(diagonal(i), WithinAbs(gathered_true_diagonal(i),
-                                      1.0e-14 * std::abs(diagonal(i))));
-  }
 }

tests/operators/prepared_hydrostatic_equilibrium_analytic_accuracy.cpp

@@ -9,430 +9,423 @@ import mean_field;
 import test_helpers;
 
 namespace prepared_hydrostatic_analytic_solve_test_utils {
-constexpr double bernoulliConstant = 0.83;
-constexpr double enthalpyAmplitude = 0.61;
+    constexpr double bernoulliConstant = 0.83;
+    constexpr double enthalpyAmplitude = 0.61;
 
-struct AnalyticCase {
-  const char *name;
+    struct AnalyticCase {
+        const char *name;
 
-  std::array<double, 3> deformationScale;
-  std::array<double, 3> angularVelocity;
-  std::array<double, 3> rotationCenter;
-};
+        std::array<double, 3> deformationScale;
+        std::array<double, 3> angularVelocity;
+        std::array<double, 3> rotationCenter;
+    };
 
-class EnthalpyJacobianOperator final : public mfem::Operator {
-public:
-  EnthalpyJacobianOperator(
-      const int enthalpySize,
-      const mean_field::operators::PreparedHydrostaticEquilibriumOperator
-          &preparedOperator)
-      : mfem::Operator(enthalpySize), m_preparedOperator(preparedOperator) {}
+    class EnthalpyJacobianOperator final : public mfem::Operator {
+    public:
+        EnthalpyJacobianOperator(
+            const int enthalpySize,
+            const mean_field::operators::PreparedHydrostaticEquilibriumOperator &preparedOperator
+        )
+            : mfem::Operator(enthalpySize),
+              m_preparedOperator(preparedOperator) {
+        }
 
-  void Mult(const mfem::Vector &direction,
-            mfem::Vector &action) const override {
-    m_preparedOperator.ApplyEnthalpyJacobianAction(direction, action);
-  }
+        void Mult(
+            const mfem::Vector &direction,
+            mfem::Vector &action
+        ) const override {
+            m_preparedOperator.ApplyEnthalpyJacobianAction(direction, action);
+        }
 
-private:
-  const mean_field::operators::PreparedHydrostaticEquilibriumOperator
-      &m_preparedOperator;
-};
+    private:
+        const mean_field::operators::PreparedHydrostaticEquilibriumOperator &m_preparedOperator;
+    };
 
-mean_field::operators::context::hydrostatic::HydrostaticEquilibriumDependencies
-make_dependencies() {
-  return {.discretization = {.identity = 701, .revision = 2},
-          .enthalpy = {.identity = 709, .revision = 3},
-          .gravityPotential = {.identity = 719, .revision = 5},
-          .displacement = {.identity = 727, .revision = 7},
-          .rotation = {.identity = 733, .revision = 11},
-          .bernoulliConstant = {.identity = 739, .revision = 13}};
-}
+    mean_field::operators::context::hydrostatic::HydrostaticEquilibriumDependencies make_dependencies() {
+        return {
+            .discretization    = {.identity = 701, .revision = 2},
+            .enthalpy          = {.identity = 709, .revision = 3},
+            .gravityPotential  = {.identity = 719, .revision = 5},
+            .displacement      = {.identity = 727, .revision = 7},
+            .rotation          = {.identity = 733, .revision = 11},
+            .bernoulliConstant = {.identity = 739, .revision = 13}
+        };
+    }
 
-mean_field::operators::context::hydrostatic::HydrostaticEquilibriumStateView
-make_state(const mfem::Vector &enthalpy, const mfem::Vector &gravityPotential,
-           const mfem::Vector &displacement) {
-  return {.enthalpy = enthalpy,
-          .gravityPotential = gravityPotential,
-          .displacement = displacement,
-          .bernoulliConstant = bernoulliConstant};
-}
+    mean_field::operators::context::hydrostatic::HydrostaticEquilibriumStateView make_state(
+        const mfem::Vector &enthalpy,
+        const mfem::Vector &gravityPotential,
+        const mfem::Vector &displacement
+    ) {
+        return {
+            .enthalpy          = enthalpy,
+            .gravityPotential  = gravityPotential,
+            .displacement      = displacement,
+            .bernoulliConstant = bernoulliConstant
+        };
+    }
 
-mfem::Vector make_vector(const std::array<double, 3> &values) {
-  mfem::Vector vector(3);
+    mfem::Vector make_vector(
+        const std::array<
+            double,
+            3> &values
+    ) {
+        mfem::Vector vector(3);
 
-  for (int component = 0; component < 3; ++component) {
-    vector(component) = values[static_cast<std::size_t>(component)];
-  }
+        for (int component = 0; component < 3; ++component) {
+            vector(component) = values[static_cast<std::size_t>(component)];
+        }
 
-  return vector;
-}
+        return vector;
+    }
 
-mean_field::physics::RigidRotation
-make_rotation(const AnalyticCase &analyticCase) {
-  return mean_field::physics::RigidRotation(
-      make_vector(analyticCase.angularVelocity),
-      make_vector(analyticCase.rotationCenter));
-}
+    mean_field::physics::RigidRotation make_rotation(const AnalyticCase &analyticCase) {
+        return mean_field::physics::RigidRotation(
+            make_vector(analyticCase.angularVelocity), make_vector(analyticCase.rotationCenter)
+        );
+    }
 
-void map_to_physical(const mfem::Vector &referencePosition,
-                     const AnalyticCase &analyticCase,
-                     mfem::Vector &physicalPosition) {
-  physicalPosition.SetSize(3);
+    void map_to_physical(
+        const mfem::Vector &referencePosition,
+        const AnalyticCase &analyticCase,
+        mfem::Vector &physicalPosition
+    ) {
+        physicalPosition.SetSize(3);
 
-  for (int component = 0; component < 3; ++component) {
-    physicalPosition(component) =
-        analyticCase.deformationScale[static_cast<std::size_t>(component)] *
-        referencePosition(component);
-  }
-}
+        for (int component = 0; component < 3; ++component) {
+            physicalPosition(component) =
+                analyticCase.deformationScale[static_cast<std::size_t>(component)] * referencePosition(component);
+        }
+    }
 
-double exact_enthalpy_value(const mfem::Vector &referencePosition) {
-  double normalizedRadiusSquared = 0.0;
+    double exact_enthalpy_value(const mfem::Vector &referencePosition) {
+        double normalizedRadiusSquared = 0.0;
 
-  for (int component = 0; component < 3; ++component) {
-    const double normalizedCoordinate =
-        referencePosition(component) / mean_field::utils::RADIUS;
+        for (int component = 0; component < 3; ++component) {
+            const double normalizedCoordinate = referencePosition(component) / mean_field::utils::RADIUS;
 
-    normalizedRadiusSquared += normalizedCoordinate * normalizedCoordinate;
-  }
+            normalizedRadiusSquared += normalizedCoordinate * normalizedCoordinate;
+        }
 
-  return enthalpyAmplitude * std::max(0.0, 1.0 - normalizedRadiusSquared);
-}
+        return enthalpyAmplitude * std::max(0.0, 1.0 - normalizedRadiusSquared);
+    }
 
-double
-exact_potential_value(const mfem::Vector &referencePosition,
-                      const AnalyticCase &analyticCase,
-                      const mean_field::physics::RigidRotation &rotation) {
-  mfem::Vector physicalPosition;
+    double exact_potential_value(
+        const mfem::Vector &referencePosition,
+        const AnalyticCase &analyticCase,
+        const mean_field::physics::RigidRotation &rotation
+    ) {
+        mfem::Vector physicalPosition;
 
-  map_to_physical(referencePosition, analyticCase, physicalPosition);
+        map_to_physical(referencePosition, analyticCase, physicalPosition);
 
-  /*
-   * Construct Phi so that
-   *
-   *     h + Phi - Psi_rotation - C = 0
-   *
-   * analytically.
-   */
-  return bernoulliConstant + rotation.potential(physicalPosition) -
-         exact_enthalpy_value(referencePosition);
-}
+        /*
+         * Construct Phi so that
+         *
+         *     h + Phi - Psi_rotation - C = 0
+         *
+         * analytically.
+         */
+        return bernoulliConstant + rotation.potential(physicalPosition) - exact_enthalpy_value(referencePosition);
+    }
 
-mfem::Array<int> make_stellar_element_marker(const mean_field::fem::FEM &f) {
-  mfem::Array<int> stellarElementMarker(f.mesh->GetNE());
+    mfem::Array<int> make_stellar_element_marker(const mean_field::fem::FEM &f) {
+        mfem::Array<int> stellarElementMarker(f.mesh->GetNE());
 
-  const int vacuumAttribute = field_dof_test_utils::vacuum_material_attribute;
+        const int vacuumAttribute = field_dof_test_utils::vacuum_material_attribute;
 
-  for (int elementId = 0; elementId < f.mesh->GetNE(); ++elementId) {
-    stellarElementMarker[elementId] =
-        f.mesh->GetAttribute(elementId) != vacuumAttribute;
-  }
+        for (int elementId = 0; elementId < f.mesh->GetNE(); ++elementId) {
+            stellarElementMarker[elementId] = f.mesh->GetAttribute(elementId) != vacuumAttribute;
+        }
 
-  return stellarElementMarker;
-}
+        return stellarElementMarker;
+    }
 } // namespace prepared_hydrostatic_analytic_solve_test_utils
 
-TEST_CASE("Prepared Hydrostatic Operator Solves Analytic Bernoulli Equilibria",
-          tags::barotrope_hydrostatic_prepared_analytic &tags::convergence
-              &tags::accuracy) {
-  using prepared_hydrostatic_analytic_solve_test_utils::AnalyticCase;
-
-  constexpr double deformationX = 1.08;
-  constexpr double deformationY = 0.96;
-
-  /*
-   * The third scale makes the affine deformation
-   * volume-preserving:
-   *
-   *     det(F) = sx * sy * sz = 1.
-   */
-  constexpr double deformationZ = 1.0 / (deformationX * deformationY);
-
-  const std::array<AnalyticCase, 3> analyticCases{
-      {{.name = "spherical nonrotating equilibrium",
-        .deformationScale = {1.0, 1.0, 1.0},
-        .angularVelocity = {0.0, 0.0, 0.0},
-        .rotationCenter = {0.0, 0.0, 0.0}},
-       {.name = "spherical rotating equilibrium",
-        .deformationScale = {1.0, 1.0, 1.0},
-        .angularVelocity = {0.13, -0.09, 0.31},
-        .rotationCenter = {0.04, -0.03, 0.02}},
-       {.name = "volume-preserving deformed rotating equilibrium",
-        .deformationScale = {deformationX, deformationY, deformationZ},
-        .angularVelocity = {0.17, -0.12, 0.43},
-        .rotationCenter = {0.031, -0.024, 0.018}}}};
+TEST_CASE(
+    "Prepared Hydrostatic Operator Solves Analytic Bernoulli Equilibria",
+    tags::barotrope_hydrostatic_prepared_analytic &tags::convergence &tags::accuracy
+) {
+    using prepared_hydrostatic_analytic_solve_test_utils::AnalyticCase;
 
-  auto args = test_utils::setup_args();
+    constexpr double deformationX = 1.08;
+    constexpr double deformationY = 0.96;
 
-  mean_field::fem::FEM f = mean_field::fem::setup_fem(args.mesh_file, args, 0);
+    /*
+     * The third scale makes the affine deformation
+     * volume-preserving:
+     *
+     *     det(F) = sx * sy * sz = 1.
+     */
+    constexpr double deformationZ = 1.0 / (deformationX * deformationY);
 
-  const MPI_Comm communicator = f.mesh->GetComm();
+    const std::array<AnalyticCase, 3> analyticCases{
+        {{.name             = "spherical nonrotating equilibrium",
+          .deformationScale = {1.0, 1.0, 1.0},
+          .angularVelocity  = {0.0, 0.0, 0.0},
+          .rotationCenter   = {0.0, 0.0, 0.0}},
+         {.name             = "spherical rotating equilibrium",
+          .deformationScale = {1.0, 1.0, 1.0},
+          .angularVelocity  = {0.13, -0.09, 0.31},
+          .rotationCenter   = {0.04, -0.03, 0.02}},
+         {.name             = "volume-preserving deformed rotating equilibrium",
+          .deformationScale = {deformationX, deformationY, deformationZ},
+          .angularVelocity  = {0.17, -0.12, 0.43},
+          .rotationCenter   = {0.031, -0.024, 0.018}}}
+    };
 
-  const mean_field::field::FieldDofMap enthalpyMap =
-      field_dof_test_utils::make_map<mean_field::field::Enthalpy>(
-          *f.enthalpyFes);
+    auto args                   = test_utils::setup_args();
 
-  const mean_field::field::FieldDofMap gravityPotentialMap =
-      field_dof_test_utils::make_map<mean_field::field::Gravity>(
-          *f.gravityPotentialFes);
+    mean_field::fem::FEM f      = mean_field::fem::setup_fem(args.mesh_file, args, 0);
 
-  const mean_field::field::FieldDofMap displacementMap =
-      field_dof_test_utils::make_map<mean_field::field::Displacement>(
-          *f.displacementFes);
+    const MPI_Comm communicator = f.mesh->GetComm();
 
-  const mfem::Array<int> stellarElementMarker =
-      prepared_hydrostatic_analytic_solve_test_utils::
-          make_stellar_element_marker(f);
+    const mean_field::field::FieldDofMap enthalpyMap =
+        field_dof_test_utils::make_map<mean_field::field::Enthalpy>(*f.enthalpyFes);
 
-  for (const AnalyticCase &analyticCase : analyticCases) {
-    DYNAMIC_SECTION(analyticCase.name) {
-      const double deformationDeterminant = analyticCase.deformationScale[0] *
-                                            analyticCase.deformationScale[1] *
-                                            analyticCase.deformationScale[2];
+    const mean_field::field::FieldDofMap gravityPotentialMap =
+        field_dof_test_utils::make_map<mean_field::field::Gravity>(*f.gravityPotentialFes);
 
-      REQUIRE(std::abs(deformationDeterminant - 1.0) < 2.0e-14);
+    const mean_field::field::FieldDofMap displacementMap =
+        field_dof_test_utils::make_map<mean_field::field::Displacement>(*f.displacementFes);
 
-      const mean_field::physics::RigidRotation rotation =
-          prepared_hydrostatic_analytic_solve_test_utils::make_rotation(
-              analyticCase);
+    const mfem::Array<int> stellarElementMarker =
+        prepared_hydrostatic_analytic_solve_test_utils::make_stellar_element_marker(f);
 
-      auto displacementFunction =
-          [&analyticCase](const mfem::Vector &referencePosition,
-                          mfem::Vector &displacementValue) {
-            mfem::Vector physicalPosition;
+    for (const AnalyticCase &analyticCase : analyticCases) {
+        DYNAMIC_SECTION(analyticCase.name) {
+            const double deformationDeterminant =
+                analyticCase.deformationScale[0] * analyticCase.deformationScale[1] * analyticCase.deformationScale[2];
 
-            prepared_hydrostatic_analytic_solve_test_utils::map_to_physical(
-                referencePosition, analyticCase, physicalPosition);
+            REQUIRE(std::abs(deformationDeterminant - 1.0) < 2.0e-14);
 
-            displacementValue.SetSize(3);
-            displacementValue = physicalPosition;
-            displacementValue -= referencePosition;
-          };
+            const mean_field::physics::RigidRotation rotation =
+                prepared_hydrostatic_analytic_solve_test_utils::make_rotation(analyticCase);
 
-      auto potentialFunction = [&analyticCase, &rotation](
-                                   const mfem::Vector &referencePosition) {
-        return prepared_hydrostatic_analytic_solve_test_utils::
-            exact_potential_value(referencePosition, analyticCase, rotation);
-      };
+            auto displacementFunction =
+                [&analyticCase](const mfem::Vector &referencePosition, mfem::Vector &displacementValue) {
+                    mfem::Vector physicalPosition;
 
-      auto enthalpyFunction = [](const mfem::Vector &referencePosition) {
-        return prepared_hydrostatic_analytic_solve_test_utils::
-            exact_enthalpy_value(referencePosition);
-      };
+                    prepared_hydrostatic_analytic_solve_test_utils::map_to_physical(
+                        referencePosition, analyticCase, physicalPosition
+                    );
 
-      mfem::VectorFunctionCoefficient displacementCoefficient(
-          f.mesh->Dimension(), displacementFunction);
+                    displacementValue.SetSize(3);
+                    displacementValue = physicalPosition;
+                    displacementValue -= referencePosition;
+                };
 
-      mfem::FunctionCoefficient potentialCoefficient(potentialFunction);
+            auto potentialFunction = [&analyticCase, &rotation](const mfem::Vector &referencePosition) {
+                return prepared_hydrostatic_analytic_solve_test_utils::exact_potential_value(
+                    referencePosition, analyticCase, rotation
+                );
+            };
 
-      mfem::FunctionCoefficient exactEnthalpyCoefficient(enthalpyFunction);
+            auto enthalpyFunction = [](const mfem::Vector &referencePosition) {
+                return prepared_hydrostatic_analytic_solve_test_utils::exact_enthalpy_value(referencePosition);
+            };
 
-      /*
-       * Project the prescribed geometry and potential.
-       */
-      mfem::ParGridFunction displacementField(f.displacementFes.get());
+            mfem::VectorFunctionCoefficient displacementCoefficient(f.mesh->Dimension(), displacementFunction);
 
-      mfem::ParGridFunction potentialField(f.gravityPotentialFes.get());
+            mfem::FunctionCoefficient potentialCoefficient(potentialFunction);
 
-      displacementField.ProjectCoefficient(displacementCoefficient);
+            mfem::FunctionCoefficient exactEnthalpyCoefficient(enthalpyFunction);
 
-      potentialField.ProjectCoefficient(potentialCoefficient);
+            /*
+             * Project the prescribed geometry and potential.
+             */
+            mfem::ParGridFunction displacementField(f.displacementFes.get());
 
-      mfem::Vector displacementTrue;
-      mfem::Vector gravityPotentialTrue;
+            mfem::ParGridFunction potentialField(f.gravityPotentialFes.get());
 
-      displacementField.GetTrueDofs(displacementTrue);
-      potentialField.GetTrueDofs(gravityPotentialTrue);
+            displacementField.ProjectCoefficient(displacementCoefficient);
 
-      const mfem::Vector displacement =
-          displacementMap.gather(displacementTrue);
-      const mfem::Vector gravityPotential =
-          gravityPotentialMap.gather(gravityPotentialTrue);
+            potentialField.ProjectCoefficient(potentialCoefficient);
 
-      /*
-       * This projection is not used as the solution. It gives
-       * the best directly available representation baseline
-       * against which the solved field can be compared.
-       */
-      mfem::ParGridFunction projectedEnthalpyField(f.enthalpyFes.get());
+            mfem::Vector displacementTrue;
+            mfem::Vector gravityPotentialTrue;
 
-      projectedEnthalpyField.ProjectCoefficient(exactEnthalpyCoefficient);
+            displacementField.GetTrueDofs(displacementTrue);
+            potentialField.GetTrueDofs(gravityPotentialTrue);
 
-      mfem::ParGridFunction zeroEnthalpyField(f.enthalpyFes.get());
+            const mfem::Vector displacement     = displacementMap.gather(displacementTrue);
+            const mfem::Vector gravityPotential = gravityPotentialMap.gather(gravityPotentialTrue);
 
-      zeroEnthalpyField = 0.0;
+            /*
+             * This projection is not used as the solution. It gives
+             * the best directly available representation baseline
+             * against which the solved field can be compared.
+             */
+            mfem::ParGridFunction projectedEnthalpyField(f.enthalpyFes.get());
 
-      const double exactEnthalpyNorm = zeroEnthalpyField.ComputeL2Error(
-          exactEnthalpyCoefficient, nullptr, &stellarElementMarker);
+            projectedEnthalpyField.ProjectCoefficient(exactEnthalpyCoefficient);
 
-      const double projectionError = projectedEnthalpyField.ComputeL2Error(
-          exactEnthalpyCoefficient, nullptr, &stellarElementMarker);
+            mfem::ParGridFunction zeroEnthalpyField(f.enthalpyFes.get());
 
-      REQUIRE(exactEnthalpyNorm > 0.0);
+            zeroEnthalpyField = 0.0;
 
-      const double relativeProjectionError =
-          projectionError / exactEnthalpyNorm;
+            const double exactEnthalpyNorm =
+                zeroEnthalpyField.ComputeL2Error(exactEnthalpyCoefficient, nullptr, &stellarElementMarker);
 
-      /*
-       * Begin deliberately far from equilibrium.
-       */
-      mfem::Vector enthalpy(enthalpyMap.reduced_size());
+            const double projectionError =
+                projectedEnthalpyField.ComputeL2Error(exactEnthalpyCoefficient, nullptr, &stellarElementMarker);
 
-      enthalpy = 0.0;
+            REQUIRE(exactEnthalpyNorm > 0.0);
 
-      auto dependencies =
-          prepared_hydrostatic_analytic_solve_test_utils::make_dependencies();
+            const double relativeProjectionError = projectionError / exactEnthalpyNorm;
 
-      mean_field::operators::PreparedHydrostaticEquilibriumOperator
-          preparedOperator(f, *f.domainMapperStateless);
+            /*
+             * Begin deliberately far from equilibrium.
+             */
+            mfem::Vector enthalpy(enthalpyMap.reduced_size());
 
-      const auto initialReport = preparedOperator.Prepare(
-          prepared_hydrostatic_analytic_solve_test_utils::make_state(
-              enthalpy, gravityPotential, displacement),
-          dependencies, rotation);
+            enthalpy          = 0.0;
 
-      REQUIRE(initialReport.preparedResidual);
-      REQUIRE(initialReport.preparedAlgebraicJacobianBlocks);
+            auto dependencies = prepared_hydrostatic_analytic_solve_test_utils::make_dependencies();
 
-      mfem::Vector initialResidual;
+            mean_field::operators::PreparedHydrostaticEquilibriumOperator preparedOperator(f, *f.domainMapperStateless);
 
-      preparedOperator.BuildResidual(initialResidual);
+            const auto initialReport = preparedOperator.Prepare(
+                prepared_hydrostatic_analytic_solve_test_utils::make_state(enthalpy, gravityPotential, displacement),
+                dependencies, rotation
+            );
 
-      const double initialResidualNorm =
-          gravity_prepared_test_utils::global_norm(initialResidual,
-                                                   communicator);
+            REQUIRE(initialReport.preparedResidual);
+            REQUIRE(initialReport.preparedAlgebraicJacobianBlocks);
 
-      REQUIRE(initialResidualNorm > 1.0e-12);
+            mfem::Vector initialResidual;
 
-      /*
-       * One discrete Newton step:
-       *
-       *     M_h delta_h = -R_h.
-       *
-       * The full four-block Bernoulli Jacobian is rectangular
-       * and underdetermined in isolation. Freezing Phi, C,
-       * rotation, and displacement makes this a well-defined
-       * enthalpy solve.
-       */
-      prepared_hydrostatic_analytic_solve_test_utils::EnthalpyJacobianOperator
-          enthalpyJacobian(enthalpyMap.reduced_size(), preparedOperator);
+            preparedOperator.BuildResidual(initialResidual);
 
-      mfem::Vector rightHandSide(initialResidual);
-      rightHandSide *= -1.0;
+            const double initialResidualNorm = gravity_prepared_test_utils::global_norm(initialResidual, communicator);
 
-      mfem::Vector enthalpyCorrection(enthalpyMap.reduced_size());
+            REQUIRE(initialResidualNorm > 1.0e-12);
 
-      enthalpyCorrection = 0.0;
+            /*
+             * One discrete Newton step:
+             *
+             *     M_h delta_h = -R_h.
+             *
+             * The full four-block Bernoulli Jacobian is rectangular
+             * and underdetermined in isolation. Freezing Phi, C,
+             * rotation, and displacement makes this a well-defined
+             * enthalpy solve.
+             */
+            prepared_hydrostatic_analytic_solve_test_utils::EnthalpyJacobianOperator enthalpyJacobian(
+                enthalpyMap.reduced_size(), preparedOperator
+            );
 
-      /*
-       * The reduced operator contains only stellar-supported
-       * enthalpy DOFs and is positive definite. MINRES remains
-       * appropriate for this symmetric system.
-       */
-      mfem::MINRESSolver linearSolver(communicator);
+            mfem::Vector rightHandSide(initialResidual);
+            rightHandSide *= -1.0;
 
-      linearSolver.SetOperator(enthalpyJacobian);
+            mfem::Vector enthalpyCorrection(enthalpyMap.reduced_size());
 
-      linearSolver.SetRelTol(1.0e-13);
-      linearSolver.SetAbsTol(1.0e-14);
-      linearSolver.SetMaxIter(2000);
-      linearSolver.SetPrintLevel(0);
+            enthalpyCorrection = 0.0;
 
-      linearSolver.Mult(rightHandSide, enthalpyCorrection);
+            /*
+             * The reduced operator contains only stellar-supported
+             * enthalpy DOFs and is positive definite. MINRES remains
+             * appropriate for this symmetric system.
+             */
+            mfem::MINRESSolver linearSolver(communicator);
 
-      INFO("Linear solver converged = " << linearSolver.GetConverged());
+            linearSolver.SetOperator(enthalpyJacobian);
 
-      INFO("Linear solver iterations = " << linearSolver.GetNumIterations());
+            linearSolver.SetRelTol(1.0e-13);
+            linearSolver.SetAbsTol(1.0e-14);
+            linearSolver.SetMaxIter(2000);
+            linearSolver.SetPrintLevel(0);
 
-      INFO("Linear solver final norm = " << linearSolver.GetFinalNorm());
+            linearSolver.Mult(rightHandSide, enthalpyCorrection);
 
-      REQUIRE(linearSolver.GetConverged());
+            INFO("Linear solver converged = " << linearSolver.GetConverged());
 
-      enthalpy += enthalpyCorrection;
+            INFO("Linear solver iterations = " << linearSolver.GetNumIterations());
 
-      /*
-       * Only the enthalpy state changed. Geometry, rotation,
-       * and algebraic Jacobian data must remain reusable.
-       */
-      ++dependencies.enthalpy.revision;
+            INFO("Linear solver final norm = " << linearSolver.GetFinalNorm());
 
-      const auto solvedReport = preparedOperator.Prepare(
-          prepared_hydrostatic_analytic_solve_test_utils::make_state(
-              enthalpy, gravityPotential, displacement),
-          dependencies, rotation);
+            REQUIRE(linearSolver.GetConverged());
 
-      CHECK(solvedReport.contextReport.updatedEnthalpy);
+            enthalpy += enthalpyCorrection;
 
-      CHECK(solvedReport.contextReport.preparedBaseState);
+            /*
+             * Only the enthalpy state changed. Geometry, rotation,
+             * and algebraic Jacobian data must remain reusable.
+             */
+            ++dependencies.enthalpy.revision;
 
-      CHECK_FALSE(solvedReport.contextReport.preparedGeometryState);
+            const auto solvedReport = preparedOperator.Prepare(
+                prepared_hydrostatic_analytic_solve_test_utils::make_state(enthalpy, gravityPotential, displacement),
+                dependencies, rotation
+            );
 
-      CHECK_FALSE(solvedReport.preparedAlgebraicJacobianBlocks);
+            CHECK(solvedReport.contextReport.updatedEnthalpy);
 
-      mfem::Vector solvedResidual;
+            CHECK(solvedReport.contextReport.preparedBaseState);
 
-      preparedOperator.BuildResidual(solvedResidual);
+            CHECK_FALSE(solvedReport.contextReport.preparedGeometryState);
 
-      const double solvedResidualNorm =
-          gravity_prepared_test_utils::global_norm(solvedResidual,
-                                                   communicator);
+            CHECK_FALSE(solvedReport.preparedAlgebraicJacobianBlocks);
 
-      const double residualReduction = solvedResidualNorm / initialResidualNorm;
+            mfem::Vector solvedResidual;
 
-      /*
-       * Compare the solved field with the continuum analytic
-       * enthalpy over stellar elements only.
-       *
-       * All three mappings have determinant one, so this
-       * normalized L2 error is also unchanged by the physical
-       * volume transformation.
-       */
-      mfem::ParGridFunction solvedEnthalpyField(f.enthalpyFes.get());
+            preparedOperator.BuildResidual(solvedResidual);
 
-      mfem::Vector enthalpyTrue(enthalpyMap.full_size());
-      enthalpyMap.scatter(enthalpy, enthalpyTrue);
-      solvedEnthalpyField.SetFromTrueDofs(enthalpyTrue);
+            const double solvedResidualNorm = gravity_prepared_test_utils::global_norm(solvedResidual, communicator);
 
-      const double solvedAnalyticError = solvedEnthalpyField.ComputeL2Error(
-          exactEnthalpyCoefficient, nullptr, &stellarElementMarker);
+            const double residualReduction  = solvedResidualNorm / initialResidualNorm;
 
-      const double relativeSolvedAnalyticError =
-          solvedAnalyticError / exactEnthalpyNorm;
+            /*
+             * Compare the solved field with the continuum analytic
+             * enthalpy over stellar elements only.
+             *
+             * All three mappings have determinant one, so this
+             * normalized L2 error is also unchanged by the physical
+             * volume transformation.
+             */
+            mfem::ParGridFunction solvedEnthalpyField(f.enthalpyFes.get());
 
-      INFO("Deformation determinant = " << deformationDeterminant);
+            mfem::Vector enthalpyTrue(enthalpyMap.full_size());
+            enthalpyMap.scatter(enthalpy, enthalpyTrue);
+            solvedEnthalpyField.SetFromTrueDofs(enthalpyTrue);
 
-      INFO("Initial weak residual norm = " << initialResidualNorm);
+            const double solvedAnalyticError =
+                solvedEnthalpyField.ComputeL2Error(exactEnthalpyCoefficient, nullptr, &stellarElementMarker);
 
-      INFO("Solved weak residual norm = " << solvedResidualNorm);
+            const double relativeSolvedAnalyticError = solvedAnalyticError / exactEnthalpyNorm;
 
-      INFO("Weak residual reduction = " << residualReduction);
+            INFO("Deformation determinant = " << deformationDeterminant);
 
-      INFO("Relative analytic projection floor = " << relativeProjectionError);
+            INFO("Initial weak residual norm = " << initialResidualNorm);
 
-      INFO("Relative solved analytic L2 error = "
-           << relativeSolvedAnalyticError);
+            INFO("Solved weak residual norm = " << solvedResidualNorm);
 
-      /*
-       * The discrete Bernoulli equation must be solved essentially
-       * to the linear-solver floor.
-       */
-      CHECK(residualReduction < 1.0e-10);
+            INFO("Weak residual reduction = " << residualReduction);
 
-      /*
-       * The directly projected analytic enthalpy provides a lower
-       * representation bound, but it is not the expected solution
-       * of the cross-space discrete Bernoulli equation. The latter
-       * also contains potential-projection and mapped-space
-       * compatibility errors.
-       */
-      CHECK(relativeSolvedAnalyticError <
-            std::max(5.0 * relativeProjectionError, 1.25e-4));
+            INFO("Relative analytic projection floor = " << relativeProjectionError);
 
-      /*
-       * Record that the analytic error remains within one order of
-       * magnitude of the direct enthalpy projection floor.
-       */
-      CHECK(relativeSolvedAnalyticError / relativeProjectionError < 5.0);
+            INFO("Relative solved analytic L2 error = " << relativeSolvedAnalyticError);
+
+            /*
+             * The discrete Bernoulli equation must be solved essentially
+             * to the linear-solver floor.
+             */
+            CHECK(residualReduction < 1.0e-10);
+
+            /*
+             * The directly projected analytic enthalpy provides a lower
+             * representation bound, but it is not the expected solution
+             * of the cross-space discrete Bernoulli equation. The latter
+             * also contains potential-projection and mapped-space
+             * compatibility errors.
+             */
+            CHECK(relativeSolvedAnalyticError < std::max(5.0 * relativeProjectionError, 1.25e-4));
+
+            /*
+             * Record that the analytic error remains within one order of
+             * magnitude of the direct enthalpy projection floor.
+             */
+            CHECK(relativeSolvedAnalyticError / relativeProjectionError < 5.0);
+        }
     }
-  }
 }

tests/operators/prepared_hydrostatic_equilibrium_complete_jacobian.cpp

@@ -138,9 +138,7 @@ TEST_CASE(
     mean_field::operators::PreparedHydrostaticEquilibriumOperator preparedOperator(f, *f.domainMapperStateless);
 
     const mfem::Vector enthalpy =
-        field_dof_test_utils::make_deterministic_supported_vector<mean_field::field::Enthalpy>(
-            *f.enthalpyFes, 0.34
-        );
+        field_dof_test_utils::make_deterministic_supported_vector<mean_field::field::Enthalpy>(*f.enthalpyFes, 0.34);
 
     const mfem::Vector gravityPotential =
         field_dof_test_utils::make_deterministic_supported_vector<mean_field::field::Gravity>(
@@ -161,9 +159,7 @@ TEST_CASE(
     );
 
     const mfem::Vector enthalpyVariation =
-        field_dof_test_utils::make_deterministic_supported_vector<mean_field::field::Enthalpy>(
-            *f.enthalpyFes, 1.07
-        );
+        field_dof_test_utils::make_deterministic_supported_vector<mean_field::field::Enthalpy>(*f.enthalpyFes, 1.07);
 
     const mfem::Vector gravityPotentialVariation =
         field_dof_test_utils::make_deterministic_supported_vector<mean_field::field::Gravity>(
@@ -236,9 +232,7 @@ TEST_CASE(
     mean_field::operators::PreparedHydrostaticEquilibriumOperator preparedOperator(f, *f.domainMapperStateless);
 
     const mfem::Vector enthalpy =
-        field_dof_test_utils::make_deterministic_supported_vector<mean_field::field::Enthalpy>(
-            *f.enthalpyFes, 0.41
-        );
+        field_dof_test_utils::make_deterministic_supported_vector<mean_field::field::Enthalpy>(*f.enthalpyFes, 0.41);
 
     const mfem::Vector gravityPotential =
         field_dof_test_utils::make_deterministic_supported_vector<mean_field::field::Gravity>(
@@ -277,9 +271,7 @@ TEST_CASE(
     CHECK(preparedOperator.GetEnthalpyMap().inactive_size() > 0);
 
     const mfem::Vector enthalpyVariation =
-        field_dof_test_utils::make_deterministic_supported_vector<mean_field::field::Enthalpy>(
-            *f.enthalpyFes, 1.12
-        );
+        field_dof_test_utils::make_deterministic_supported_vector<mean_field::field::Enthalpy>(*f.enthalpyFes, 1.12);
 
     const mfem::Vector gravityPotentialVariation =
         field_dof_test_utils::make_deterministic_supported_vector<mean_field::field::Gravity>(

tests/operators/prepared_mass_normalization.cpp

@@ -26,16 +26,13 @@ namespace mass_normalization_test_utils {
     );
 
     [[nodiscard]] mean_field::operators::MassNormalizationLayout make_layout(const mean_field::fem::FEM &f) {
-        const auto densityMap =
-            field_dof_test_utils::make_map<mean_field::field::Density>(*f.densityFes);
+        const auto densityMap = field_dof_test_utils::make_map<mean_field::field::Density>(*f.densityFes);
         const auto displacementMap =
             field_dof_test_utils::make_map<mean_field::field::Displacement>(*f.displacementFes);
-        const auto gravityFluxMap =
-            field_dof_test_utils::make_map<mean_field::field::Gravity>(*f.gravityFluxFes);
+        const auto gravityFluxMap = field_dof_test_utils::make_map<mean_field::field::Gravity>(*f.gravityFluxFes);
         const auto gravityPotentialMap =
             field_dof_test_utils::make_map<mean_field::field::Gravity>(*f.gravityPotentialFes);
-        const auto enthalpyMap =
-            field_dof_test_utils::make_map<mean_field::field::Enthalpy>(*f.enthalpyFes);
+        const auto enthalpyMap = field_dof_test_utils::make_map<mean_field::field::Enthalpy>(*f.enthalpyFes);
 
         const std::array<int, CoupledForm::value_block_count> valueSizes{
             densityMap.reduced_size(),          displacementMap.reduced_size(), gravityFluxMap.reduced_size(),
@@ -43,7 +40,7 @@ namespace mass_normalization_test_utils {
         };
 
         const std::array<int, CoupledForm::residual_block_count> residualSizes{
-            gravityFluxMap.reduced_size(), gravityPotentialMap.reduced_size(), densityMap.reduced_size(),
+            gravityFluxMap.reduced_size(),  gravityPotentialMap.reduced_size(), densityMap.reduced_size(),
             displacementMap.reduced_size(), enthalpyMap.reduced_size(),         1
         };
 
@@ -345,8 +342,7 @@ TEST_CASE(
     mean_field::operators::PreparedMassNormalizationOperator massOperator(f, *f.domainMapperStateless, gravityContext);
     massOperator.Prepare({.targetMass = 1.11}, dependencies);
 
-    const mfem::Vector reducedDisplacementDirection =
-        gravityContext.GetDisplacementMap().gather(displacementDirection);
+    const mfem::Vector reducedDisplacementDirection = gravityContext.GetDisplacementMap().gather(displacementDirection);
 
     mfem::Vector analyticAction;
     massOperator.ApplyDisplacementJacobianAction(reducedDisplacementDirection, analyticAction);
@@ -476,9 +472,8 @@ TEST_CASE(
     mean_field::operators::PreparedMassNormalizationOperator massOperator(f, *f.domainMapperStateless, gravityContext);
     massOperator.Prepare({.targetMass = 1.19}, dependencies);
 
-    const mfem::Vector reducedDensityDirection = gravityContext.GetDensityMap().gather(densityDirection);
-    const mfem::Vector reducedDisplacementDirection =
-        gravityContext.GetDisplacementMap().gather(displacementDirection);
+    const mfem::Vector reducedDensityDirection      = gravityContext.GetDensityMap().gather(densityDirection);
+    const mfem::Vector reducedDisplacementDirection = gravityContext.GetDisplacementMap().gather(displacementDirection);
 
     mfem::Vector densityAction;
     mfem::Vector displacementAction;
@@ -486,9 +481,7 @@ TEST_CASE(
 
     massOperator.ApplyDensityJacobianAction(reducedDensityDirection, densityAction);
     massOperator.ApplyDisplacementJacobianAction(reducedDisplacementDirection, displacementAction);
-    massOperator.ApplyCompleteJacobianAction(
-        reducedDensityDirection, reducedDisplacementDirection, completeAction
-    );
+    massOperator.ApplyCompleteJacobianAction(reducedDensityDirection, reducedDisplacementDirection, completeAction);
 
     CHECK(
         mass_normalization_test_utils::relative_error(completeAction(0), densityAction(0) + displacementAction(0)) <
@@ -498,10 +491,7 @@ TEST_CASE(
     const auto layout = mass_normalization_test_utils::make_layout(f);
     mean_field::operators::PreparedMassNormalizationJacobianOperator adapter(layout, massOperator);
 
-    CHECK(
-        layout.size(mass_normalization_test_utils::densityValue) ==
-        gravityContext.GetDensityMap().reduced_size()
-    );
+    CHECK(layout.size(mass_normalization_test_utils::densityValue) == gravityContext.GetDensityMap().reduced_size());
     CHECK(
         layout.size(mass_normalization_test_utils::displacementValue) ==
         gravityContext.GetDisplacementMap().reduced_size()

tests/physics/barotrope.cpp

@@ -8,115 +8,202 @@
 import mean_field;
 import test_helpers;
 
-TEST_CASE("Polytropic EOS Satisfies Its Analytic Identities",
-          tags::barotrope_eos_unit) {
-  constexpr double polytropic_index = 3.0;
-  constexpr double polytropic_constant = 1.5;
+TEST_CASE(
+    "Polytropic EOS Satisfies Its Analytic Identities",
+    tags::barotrope_eos_unit
+) {
+    using namespace mean_field::eos;
 
-  const mean_field::eos::Polytrope barotrope(polytropic_index,
-                                             polytropic_constant);
+    constexpr double polytropic_index    = 3.0;
+    constexpr double polytropic_constant = 1.5;
 
-  const std::array<double, 5> densities{1.0e-6, 1.0e-3, 0.1, 0.7, 2.0};
+    const Polytrope barotrope(polytropic_index, polytropic_constant);
 
-  for (const double density : densities) {
-    const double pressure = barotrope.pressure_from_density(density);
+    using densityV  = DensityValue;
+    using pressureV = PressureValue;
+    using enthalpyV = SpecificEnthalpyValue;
 
-    const double enthalpy = barotrope.enthalpy_from_density(density);
+    constexpr std::array<densityV, 5> densities{
+        densityV{1.0e-6}, densityV{1.0e-3}, densityV{0.1}, densityV{0.7}, densityV{2.0}
+    };
 
-    const double reconstructed_density =
-        barotrope.density_from_enthalpy(enthalpy);
+    for (const densityV density : densities) {
+        const pressureV pressure               = evaluate<quantity::Pressure>(barotrope, density);
 
-    const double reconstructed_pressure =
-        barotrope.pressure_from_enthalpy(enthalpy);
+        const enthalpyV enthalpy               = evaluate<quantity::SpecificEnthalpy>(barotrope, density);
+        const densityV reconstructed_density   = evaluate<quantity::Density>(barotrope, enthalpy);
 
-    const double reconstructed_enthalpy =
-        barotrope.enthalpy_from_pressure(pressure);
+        const pressureV reconstructed_pressure = evaluate<quantity::Pressure>(barotrope, enthalpy);
 
-    CHECK_THAT(reconstructed_density,
-               Catch::Matchers::WithinRel(density, 2.0e-14));
+        const enthalpyV reconstructed_enthalpy = evaluate<quantity::SpecificEnthalpy>(barotrope, pressure);
 
-    CHECK_THAT(reconstructed_pressure,
-               Catch::Matchers::WithinRel(pressure, 2.0e-14));
+        CHECK_THAT(reconstructed_density.value(), Catch::Matchers::WithinRel(density.value(), 2.0e-14));
 
-    CHECK_THAT(reconstructed_enthalpy,
-               Catch::Matchers::WithinRel(enthalpy, 2.0e-14));
+        CHECK_THAT(reconstructed_pressure.value(), Catch::Matchers::WithinRel(pressure.value(), 2.0e-14));
 
-    CHECK_THAT(pressure,
-               Catch::Matchers::WithinRel(
-                   density * enthalpy / (polytropic_index + 1.0), 2.0e-14));
+        CHECK_THAT(reconstructed_enthalpy.value(), Catch::Matchers::WithinRel(enthalpy.value(), 2.0e-14));
 
-    CHECK_THAT(barotrope.pressure_derivative_from_enthalpy(enthalpy),
-               Catch::Matchers::WithinRel(density, 2.0e-14));
+        CHECK_THAT(
+            pressure.value(),
+            Catch::Matchers::WithinRel(density.value() * enthalpy.value() / (polytropic_index + 1.0), 2.0e-14)
+        );
 
-    CHECK_THAT(
-        barotrope.pressure_derivative_from_density(density),
-        Catch::Matchers::WithinRel(enthalpy / polytropic_index, 2.0e-14));
-  }
+        CHECK_THAT(
+            (mean_field::eos::partialDerivative<
+                 mean_field::eos::quantity::Pressure, mean_field::eos::quantity::SpecificEnthalpy>(
+                 barotrope, mean_field::eos::SpecificEnthalpyValue{enthalpy}
+            )
+                 .value()),
+            Catch::Matchers::WithinRel(density.value(), 2.0e-14)
+        );
+
+        CHECK_THAT(
+            (mean_field::eos::partialDerivative<
+                 mean_field::eos::quantity::Pressure, mean_field::eos::quantity::Density>(
+                 barotrope, mean_field::eos::DensityValue{density}
+            )
+                 .value()),
+            Catch::Matchers::WithinRel(enthalpy.value() / polytropic_index, 2.0e-14)
+        );
+    }
 }
 
-TEST_CASE("Polytropic EOS Derivatives Match Centered Differences",
-          tags::barotrope_eos_jacobian) {
-  const mean_field::eos::Polytrope barotrope(3.0, 1.5);
+TEST_CASE(
+    "Polytropic EOS Derivatives Match Centered Differences",
+    tags::barotrope_eos_jacobian
+) {
+    using namespace mean_field::eos;
 
-  const std::array<double, 4> enthalpies{0.05, 0.2, 0.7, 1.4};
+    const Polytrope barotrope(3.0, 1.5);
 
-  for (const double enthalpy : enthalpies) {
-    const double step = 1.0e-6 * std::max(1.0, enthalpy);
+    using densityV  = DensityValue;
+    using pressureV = PressureValue;
+    using enthalpyV = SpecificEnthalpyValue;
 
-    const double density_difference =
-        (barotrope.density_from_enthalpy(enthalpy + step) -
-         barotrope.density_from_enthalpy(enthalpy - step)) /
-        (2.0 * step);
+    constexpr std::array<enthalpyV, 4> enthalpies{enthalpyV{0.05}, enthalpyV{0.2}, enthalpyV{0.7}, enthalpyV{1.4}};
 
-    const double pressure_difference =
-        (barotrope.pressure_from_enthalpy(enthalpy + step) -
-         barotrope.pressure_from_enthalpy(enthalpy - step)) /
-        (2.0 * step);
+    for (const enthalpyV enthalpy : enthalpies) {
+        const enthalpyV step                = enthalpyV{1.0e-6} * std::max(1.0, enthalpy.value());
 
-    CHECK_THAT(
-        density_difference,
-        Catch::Matchers::WithinRel(
-            barotrope.density_derivative_from_enthalpy(enthalpy), 5.0e-10));
+        const densityV density_difference   = (evaluate<quantity::Density>(barotrope, enthalpy + step) -
+                                               evaluate<quantity::Density>(barotrope, enthalpy - step)) /
+                                              (2.0 * step.value());
 
-    CHECK_THAT(
-        pressure_difference,
-        Catch::Matchers::WithinRel(
-            barotrope.pressure_derivative_from_enthalpy(enthalpy), 5.0e-10));
-  }
+        const pressureV pressure_difference = (evaluate<quantity::Pressure>(barotrope, enthalpy + step) -
+                                               evaluate<quantity::Pressure>(barotrope, enthalpy - step)) /
+                                              (2.0 * step.value());
+
+        CHECK_THAT(
+            density_difference.value(),
+            Catch::Matchers::WithinRel(
+                mean_field::eos::partialDerivative<
+                    mean_field::eos::quantity::Density, mean_field::eos::quantity::SpecificEnthalpy>(
+                    barotrope, enthalpy
+                )
+                    .value(),
+                5.0e-10
+            )
+        );
+
+        CHECK_THAT(
+            pressure_difference.value(),
+            Catch::Matchers::WithinRel(
+                mean_field::eos::partialDerivative<
+                    mean_field::eos::quantity::Pressure, mean_field::eos::quantity::SpecificEnthalpy>(
+                    barotrope, enthalpy
+                )
+                    .value(),
+                5.0e-10
+            )
+        );
+    }
 }
 
-TEST_CASE("Polytropic EOS Has An Exact Zero Density Surface",
-          tags::barotrope_eos_unit) {
-  const mean_field::eos::Polytrope barotrope(3.0, 1.5);
+TEST_CASE(
+    "Polytropic EOS Has An Exact Zero Density Surface",
+    tags::barotrope_eos_unit
+) {
+    const mean_field::eos::Polytrope barotrope(3.0, 1.5);
 
-  CHECK(barotrope.density_from_enthalpy(-1.0) == 0.0);
-  CHECK(barotrope.density_from_enthalpy(0.0) == 0.0);
+    CHECK(
+        mean_field::eos::evaluate<mean_field::eos::quantity::Density>(
+            barotrope, mean_field::eos::SpecificEnthalpyValue{-1.0}
+        )
+            .value() == 0.0
+    );
+    CHECK(
+        mean_field::eos::evaluate<mean_field::eos::quantity::Density>(
+            barotrope, mean_field::eos::SpecificEnthalpyValue{0.0}
+        )
+            .value() == 0.0
+    );
 
-  CHECK(barotrope.pressure_from_enthalpy(-1.0) == 0.0);
-  CHECK(barotrope.pressure_from_enthalpy(0.0) == 0.0);
+    CHECK(
+        mean_field::eos::evaluate<mean_field::eos::quantity::Pressure>(
+            barotrope, mean_field::eos::SpecificEnthalpyValue{-1.0}
+        )
+            .value() == 0.0
+    );
+    CHECK(
+        mean_field::eos::evaluate<mean_field::eos::quantity::Pressure>(
+            barotrope, mean_field::eos::SpecificEnthalpyValue{0.0}
+        )
+            .value() == 0.0
+    );
 
-  CHECK(barotrope.density_derivative_from_enthalpy(-1.0) == 0.0);
+    CHECK(
+        (mean_field::eos::partialDerivative<
+             mean_field::eos::quantity::Density, mean_field::eos::quantity::SpecificEnthalpy>(
+             barotrope, mean_field::eos::SpecificEnthalpyValue{-1.0}
+         )
+             .value() == 0.0)
+    );
 
-  CHECK(barotrope.density_derivative_from_enthalpy(0.0) == 0.0);
+    CHECK(
+        (mean_field::eos::partialDerivative<
+             mean_field::eos::quantity::Density, mean_field::eos::quantity::SpecificEnthalpy>(
+             barotrope, mean_field::eos::SpecificEnthalpyValue{0.0}
+         )
+             .value() == 0.0)
+    );
 
-  CHECK(barotrope.pressure_derivative_from_enthalpy(0.0) == 0.0);
+    CHECK(
+        (mean_field::eos::partialDerivative<
+             mean_field::eos::quantity::Pressure, mean_field::eos::quantity::SpecificEnthalpy>(
+             barotrope, mean_field::eos::SpecificEnthalpyValue{0.0}
+         )
+             .value() == 0.0)
+    );
 }
 
-TEST_CASE("Polytropic EOS Rejects Invalid Material Parameters",
-          tags::barotrope_eos_unit) {
-  CHECK_THROWS_AS(mean_field::eos::Polytrope(0.5, 1.0), std::invalid_argument);
+TEST_CASE(
+    "Polytropic EOS Rejects Invalid Material Parameters",
+    tags::barotrope_eos_unit
+) {
+    CHECK_THROWS_AS(mean_field::eos::Polytrope(0.5, 1.0), std::invalid_argument);
 
-  CHECK_THROWS_AS(mean_field::eos::Polytrope(3.0, 0.0), std::invalid_argument);
+    CHECK_THROWS_AS(mean_field::eos::Polytrope(3.0, 0.0), std::invalid_argument);
 
-  CHECK_THROWS_AS(
-      mean_field::eos::Polytrope(std::numeric_limits<double>::infinity(), 1.0),
-      std::invalid_argument);
+    CHECK_THROWS_AS(mean_field::eos::Polytrope(std::numeric_limits<double>::infinity(), 1.0), std::invalid_argument);
 
-  const mean_field::eos::Polytrope barotrope(3.0, 1.0);
+    const mean_field::eos::Polytrope barotrope(3.0, 1.0);
 
-  CHECK_THROWS_AS(barotrope.pressure_from_density(-1.0), std::domain_error);
+    CHECK_THROWS_AS(
+        mean_field::eos::evaluate<mean_field::eos::quantity::Pressure>(barotrope, mean_field::eos::DensityValue{-1.0}),
+        std::domain_error
+    );
 
-  CHECK_THROWS_AS(barotrope.enthalpy_from_density(-1.0), std::domain_error);
+    CHECK_THROWS_AS(
+        mean_field::eos::evaluate<mean_field::eos::quantity::SpecificEnthalpy>(
+            barotrope, mean_field::eos::DensityValue{-1.0}
+        ),
+        std::domain_error
+    );
 
-  CHECK_THROWS_AS(barotrope.enthalpy_from_pressure(-1.0), std::domain_error);
+    CHECK_THROWS_AS(
+        mean_field::eos::evaluate<mean_field::eos::quantity::SpecificEnthalpy>(
+            barotrope, mean_field::eos::PressureValue{-1.0}
+        ),
+        std::domain_error
+    );
 }

tests/physics/equation_of_state_consumer_contracts.cpp

@@ -0,0 +1,125 @@
+#include <catch2/catch_test_macros.hpp>
+
+import mean_field;
+import test_helpers;
+
+namespace {
+    namespace eos = mean_field::eos;
+
+    class DensityClosureEquationOfState final {
+    public:
+        using Relations = eos::RelationCatalog<eos::DensityFromSpecificEnthalpy>;
+
+        [[nodiscard]] constexpr eos::DensityValue evaluate(
+            eos::DensityFromSpecificEnthalpy,
+            const eos::SpecificEnthalpyValue specificEnthalpy
+        ) const noexcept {
+            return eos::DensityValue{specificEnthalpy.value()};
+        }
+
+        [[nodiscard]] constexpr eos::PartialDerivative<
+            eos::quantity::Density,
+            eos::quantity::SpecificEnthalpy>
+        partialDerivative(
+            eos::DensityFromSpecificEnthalpy,
+            eos::WithRespectTo<eos::quantity::SpecificEnthalpy>,
+            eos::SpecificEnthalpyValue
+        ) const noexcept {
+            return eos::PartialDerivative<eos::quantity::Density, eos::quantity::SpecificEnthalpy>{1.0};
+        }
+    };
+
+    class DensityClosureWithoutDerivative final {
+    public:
+        using Relations = eos::RelationCatalog<eos::DensityFromSpecificEnthalpy>;
+
+        [[nodiscard]] constexpr eos::DensityValue evaluate(
+            eos::DensityFromSpecificEnthalpy,
+            const eos::SpecificEnthalpyValue specificEnthalpy
+        ) const noexcept {
+            return eos::DensityValue{specificEnthalpy.value()};
+        }
+    };
+
+    class EnthalpyPressureEquationOfState final {
+    public:
+        using Relations = eos::RelationCatalog<eos::PressureFromSpecificEnthalpy>;
+
+        [[nodiscard]] constexpr eos::PressureValue evaluate(
+            eos::PressureFromSpecificEnthalpy,
+            const eos::SpecificEnthalpyValue specificEnthalpy
+        ) const noexcept {
+            return eos::PressureValue{2.0 * specificEnthalpy.value()};
+        }
+
+        [[nodiscard]] constexpr eos::PartialDerivative<
+            eos::quantity::Pressure,
+            eos::quantity::SpecificEnthalpy>
+        partialDerivative(
+            eos::PressureFromSpecificEnthalpy,
+            eos::WithRespectTo<eos::quantity::SpecificEnthalpy>,
+            eos::SpecificEnthalpyValue
+        ) const noexcept {
+            return eos::PartialDerivative<eos::quantity::Pressure, eos::quantity::SpecificEnthalpy>{2.0};
+        }
+    };
+
+    class DensitySeedEquationOfState final {
+    public:
+        using Relations = eos::RelationCatalog<eos::SpecificEnthalpyFromDensity>;
+
+        [[nodiscard]] constexpr eos::SpecificEnthalpyValue evaluate(
+            eos::SpecificEnthalpyFromDensity,
+            const eos::DensityValue density
+        ) const noexcept {
+            return eos::SpecificEnthalpyValue{3.0 * density.value()};
+        }
+    };
+
+    class GeneralEquationOfStateWithoutCurrentConsumerRelations final {
+    public:
+        using Relations = eos::RelationCatalog<eos::SpecificEnthalpyFromPressure>;
+
+        [[nodiscard]] constexpr eos::SpecificEnthalpyValue evaluate(
+            eos::SpecificEnthalpyFromPressure,
+            const eos::PressureValue pressure
+        ) const noexcept {
+            return eos::SpecificEnthalpyValue{pressure.value()};
+        }
+    };
+} // namespace
+
+TEST_CASE(
+    "Barotropic Closure EOS Requires Density And Its Enthalpy Derivative",
+    tags::barotropic_closure_equation_of_state_contract
+) {
+    STATIC_CHECK(eos::BarotropicClosureEquationOfState<eos::Polytrope>);
+    STATIC_CHECK(eos::BarotropicClosureEquationOfState<DensityClosureEquationOfState>);
+    STATIC_CHECK(eos::EquationOfStateModel<DensityClosureWithoutDerivative>);
+    STATIC_CHECK_FALSE(eos::BarotropicClosureEquationOfState<DensityClosureWithoutDerivative>);
+    STATIC_CHECK_FALSE(eos::BarotropicClosureEquationOfState<EnthalpyPressureEquationOfState>);
+}
+
+TEST_CASE(
+    "Pressure Force EOS Requires Pressure And Its Enthalpy Derivative",
+    tags::pressure_force_equation_of_state_contract
+) {
+    STATIC_CHECK(eos::PressureForceEquationOfState<eos::Polytrope>);
+    STATIC_CHECK(eos::PressureForceEquationOfState<EnthalpyPressureEquationOfState>);
+    STATIC_CHECK_FALSE(eos::PressureForceEquationOfState<DensityClosureEquationOfState>);
+    STATIC_CHECK_FALSE(eos::PressureForceEquationOfState<DensityClosureWithoutDerivative>);
+}
+
+TEST_CASE(
+    "Structure Seed EOS Requires Enthalpy From Density",
+    tags::structure_seed_equation_of_state_contract
+) {
+    STATIC_CHECK(eos::StructureSeedEquationOfState<eos::Polytrope>);
+    STATIC_CHECK(eos::StructureSeedEquationOfState<DensitySeedEquationOfState>);
+    STATIC_CHECK_FALSE(eos::StructureSeedEquationOfState<DensityClosureEquationOfState>);
+
+    STATIC_CHECK(eos::EquationOfStateModel<GeneralEquationOfStateWithoutCurrentConsumerRelations>);
+    STATIC_CHECK_FALSE(eos::StructureSeedEquationOfState<GeneralEquationOfStateWithoutCurrentConsumerRelations>);
+    STATIC_CHECK_FALSE(eos::BarotropicClosureEquationOfState<GeneralEquationOfStateWithoutCurrentConsumerRelations>);
+    STATIC_CHECK_FALSE(eos::PressureForceEquationOfState<GeneralEquationOfStateWithoutCurrentConsumerRelations>);
+}

tests/physics/equation_of_state_runtime_view.cpp

@@ -0,0 +1,322 @@
+#include <array>
+#include <concepts>
+#include <expected>
+#include <limits>
+#include <memory>
+#include <span>
+#include <string_view>
+#include <type_traits>
+
+#include <catch2/catch_test_macros.hpp>
+
+import mean_field;
+import test_helpers;
+
+namespace {
+    namespace eos = mean_field::eos;
+
+    class LinearPressureEquationOfState final {
+    public:
+        using Relations = eos::RelationCatalog<eos::PressureFromDensity>;
+
+        [[nodiscard]] constexpr eos::PressureValue evaluate(
+            eos::PressureFromDensity,
+            const eos::DensityValue density
+        ) const noexcept {
+            return eos::PressureValue{2.0 * density.value() + 0.5};
+        }
+    };
+
+    struct DensityAlias final : eos::ThermodynamicQuantity {
+        static constexpr std::string_view identifier = "density";
+    };
+
+    class AmbiguouslyIdentifiedEquationOfState final {
+    public:
+        using Relations = eos::RelationCatalog<eos::Relation<DensityAlias, eos::quantity::Density>>;
+
+        [[nodiscard]] constexpr eos::QuantityValue<DensityAlias> evaluate(
+            eos::Relation<
+                DensityAlias,
+                eos::quantity::Density>,
+            const eos::DensityValue density
+        ) const noexcept {
+            return eos::QuantityValue<DensityAlias>{density.value()};
+        }
+    };
+
+    [[nodiscard]] std::expected<
+        eos::PressureValue,
+        eos::EvaluationError>
+    pressureAtDensity(
+        const eos::EquationOfStateView equationOfState,
+        const eos::DensityValue density
+    ) {
+        return equationOfState.tryEvaluate<eos::quantity::Pressure>(density);
+    }
+
+    [[nodiscard]] const eos::RuntimeRelationDescriptor *findRelation(
+        const eos::EquationOfStateView equationOfState,
+        const eos::ThermodynamicQuantityId output,
+        const eos::ThermodynamicQuantityId input
+    ) {
+        for (const eos::RuntimeRelationDescriptor &relation : equationOfState.relations()) {
+            if (relation.outputQuantity == output && relation.inputQuantities.size() == 1 &&
+                relation.inputQuantities[0] == input) {
+                return std::addressof(relation);
+            }
+        }
+
+        return nullptr;
+    }
+} // namespace
+
+TEST_CASE(
+    "Runtime EOS View Generates The Polytropic Relation Catalog",
+    tags::equation_of_state_runtime_contract
+) {
+    STATIC_CHECK(eos::RuntimeEquationOfStateModel<eos::Polytrope>);
+    STATIC_CHECK(eos::RuntimeEquationOfStateModel<LinearPressureEquationOfState>);
+    STATIC_CHECK(eos::EquationOfStateModel<AmbiguouslyIdentifiedEquationOfState>);
+    STATIC_CHECK_FALSE(eos::RuntimeEquationOfStateModel<AmbiguouslyIdentifiedEquationOfState>);
+    STATIC_CHECK(std::is_trivially_copyable_v<eos::EquationOfStateView>);
+    STATIC_CHECK_FALSE(std::constructible_from<eos::EquationOfStateView, eos::Polytrope &&>);
+
+    const eos::Polytrope equationOfState(3.0, 0.25);
+    const eos::Polytrope secondEquationOfState(1.5, 0.73);
+
+    const eos::EquationOfStateView view{equationOfState};
+    const eos::EquationOfStateView secondView{secondEquationOfState};
+
+    REQUIRE(view.relations().size() == eos::Polytrope::Relations::size);
+    CHECK(view.relations().data() == secondView.relations().data());
+
+    CHECK(eos::thermodynamicQuantityId<eos::quantity::Density>.name() == "density");
+    CHECK(eos::thermodynamicQuantityId<eos::quantity::Pressure>.name() == "pressure");
+    CHECK(eos::thermodynamicQuantityId<eos::quantity::SpecificEnthalpy>.name() == "specific_enthalpy");
+
+    const eos::RuntimeRelationDescriptor *pressureFromDensity = findRelation(
+        view, eos::thermodynamicQuantityId<eos::quantity::Pressure>,
+        eos::thermodynamicQuantityId<eos::quantity::Density>
+    );
+
+    REQUIRE(pressureFromDensity != nullptr);
+    CHECK(pressureFromDensity->hasPartialDerivative(0));
+
+    const eos::RuntimeRelationDescriptor *specificEnthalpyFromPressure = findRelation(
+        view, eos::thermodynamicQuantityId<eos::quantity::SpecificEnthalpy>,
+        eos::thermodynamicQuantityId<eos::quantity::Pressure>
+    );
+
+    REQUIRE(specificEnthalpyFromPressure != nullptr);
+    CHECK_FALSE(specificEnthalpyFromPressure->hasPartialDerivative(0));
+
+    const eos::RuntimeRelationDescriptor *pressureFromSpecificEnthalpy = findRelation(
+        view, eos::thermodynamicQuantityId<eos::quantity::Pressure>,
+        eos::thermodynamicQuantityId<eos::quantity::SpecificEnthalpy>
+    );
+
+    REQUIRE(pressureFromSpecificEnthalpy != nullptr);
+    CHECK(pressureFromSpecificEnthalpy->hasPartialDerivative(0));
+
+    const eos::RuntimeRelationDescriptor *specificEnthalpyFromDensity = findRelation(
+        view, eos::thermodynamicQuantityId<eos::quantity::SpecificEnthalpy>,
+        eos::thermodynamicQuantityId<eos::quantity::Density>
+    );
+
+    REQUIRE(specificEnthalpyFromDensity != nullptr);
+    CHECK_FALSE(specificEnthalpyFromDensity->hasPartialDerivative(0));
+
+    const eos::RuntimeRelationDescriptor *densityFromSpecificEnthalpy = findRelation(
+        view, eos::thermodynamicQuantityId<eos::quantity::Density>,
+        eos::thermodynamicQuantityId<eos::quantity::SpecificEnthalpy>
+    );
+
+    REQUIRE(densityFromSpecificEnthalpy != nullptr);
+    CHECK(densityFromSpecificEnthalpy->hasPartialDerivative(0));
+}
+
+TEST_CASE(
+    "Runtime EOS View Matches Typed Polytropic Evaluation",
+    tags::equation_of_state_runtime_compatibility
+) {
+    const eos::Polytrope equationOfState(3.0, 0.25);
+    const eos::EquationOfStateView view{equationOfState};
+
+    const eos::DensityValue density{0.7};
+    const eos::SpecificEnthalpyValue specificEnthalpy{0.9};
+    const eos::PressureValue pressure{0.04};
+
+    const auto runtimePressureFromDensity          = view.tryEvaluate<eos::quantity::Pressure>(density);
+    const auto runtimePressureFromSpecificEnthalpy = view.tryEvaluate<eos::quantity::Pressure>(specificEnthalpy);
+    const auto runtimeSpecificEnthalpyFromDensity  = view.tryEvaluate<eos::quantity::SpecificEnthalpy>(density);
+    const auto runtimeSpecificEnthalpyFromPressure = view.tryEvaluate<eos::quantity::SpecificEnthalpy>(pressure);
+    const auto runtimeDensityFromSpecificEnthalpy  = view.tryEvaluate<eos::quantity::Density>(specificEnthalpy);
+
+    REQUIRE(runtimePressureFromDensity.has_value());
+    REQUIRE(runtimePressureFromSpecificEnthalpy.has_value());
+    REQUIRE(runtimeSpecificEnthalpyFromDensity.has_value());
+    REQUIRE(runtimeSpecificEnthalpyFromPressure.has_value());
+    REQUIRE(runtimeDensityFromSpecificEnthalpy.has_value());
+
+    CHECK(
+        runtimePressureFromDensity->value() == eos::evaluate<eos::quantity::Pressure>(equationOfState, density).value()
+    );
+    CHECK(
+        runtimePressureFromSpecificEnthalpy->value() ==
+        eos::evaluate<eos::quantity::Pressure>(equationOfState, specificEnthalpy).value()
+    );
+    CHECK(
+        runtimeSpecificEnthalpyFromDensity->value() ==
+        eos::evaluate<eos::quantity::SpecificEnthalpy>(equationOfState, density).value()
+    );
+    CHECK(
+        runtimeSpecificEnthalpyFromPressure->value() ==
+        eos::evaluate<eos::quantity::SpecificEnthalpy>(equationOfState, pressure).value()
+    );
+    CHECK(
+        runtimeDensityFromSpecificEnthalpy->value() ==
+        eos::evaluate<eos::quantity::Density>(equationOfState, specificEnthalpy).value()
+    );
+
+    const std::array runtimeDensityInput{
+        eos::RuntimeQuantityValue{eos::thermodynamicQuantityId<eos::quantity::Density>, density.value()}
+    };
+
+    const auto erasedPressureFromDensity = view.tryEvaluate(
+        eos::thermodynamicQuantityId<eos::quantity::Pressure>,
+        std::span<const eos::RuntimeQuantityValue>{runtimeDensityInput}
+    );
+
+    REQUIRE(erasedPressureFromDensity.has_value());
+    CHECK(erasedPressureFromDensity->quantity == eos::thermodynamicQuantityId<eos::quantity::Pressure>);
+    CHECK(erasedPressureFromDensity->value == runtimePressureFromDensity->value());
+
+    const auto runtimePressureDerivative =
+        view.tryPartialDerivative<eos::quantity::Pressure, eos::quantity::SpecificEnthalpy>(specificEnthalpy);
+
+    const auto runtimeDensityDerivative =
+        view.tryPartialDerivative<eos::quantity::Density, eos::quantity::SpecificEnthalpy>(specificEnthalpy);
+
+    const auto runtimePressureDensityDerivative =
+        view.tryPartialDerivative<eos::quantity::Pressure, eos::quantity::Density>(density);
+
+    REQUIRE(runtimePressureDerivative.has_value());
+    REQUIRE(runtimeDensityDerivative.has_value());
+    REQUIRE(runtimePressureDensityDerivative.has_value());
+
+    CHECK(
+        runtimePressureDerivative->value() ==
+        eos::partialDerivative<eos::quantity::Pressure, eos::quantity::SpecificEnthalpy>(
+            equationOfState, specificEnthalpy
+        )
+            .value()
+    );
+    CHECK(
+        runtimeDensityDerivative->value() ==
+        eos::partialDerivative<eos::quantity::Density, eos::quantity::SpecificEnthalpy>(
+            equationOfState, specificEnthalpy
+        )
+            .value()
+    );
+    CHECK(
+        runtimePressureDensityDerivative->value() ==
+        eos::partialDerivative<eos::quantity::Pressure, eos::quantity::Density>(equationOfState, density).value()
+    );
+
+    const auto erasedPressureDensityDerivative = view.tryPartialDerivative(
+        eos::thermodynamicQuantityId<eos::quantity::Pressure>, eos::thermodynamicQuantityId<eos::quantity::Density>,
+        std::span<const eos::RuntimeQuantityValue>{runtimeDensityInput}
+    );
+
+    REQUIRE(erasedPressureDensityDerivative.has_value());
+    CHECK(*erasedPressureDensityDerivative == runtimePressureDensityDerivative->value());
+}
+
+TEST_CASE(
+    "Runtime EOS View Reports Unsupported And Invalid Requests",
+    tags::equation_of_state_runtime_contract
+) {
+    const eos::Polytrope equationOfState(3.0, 0.25);
+    const eos::EquationOfStateView view{equationOfState};
+
+    constexpr eos::ThermodynamicQuantityId temperature{"temperature"};
+
+    const std::array densityInput{eos::RuntimeQuantityValue{eos::thermodynamicQuantityId<eos::quantity::Density>, 0.7}};
+
+    const std::array pressureInput{
+        eos::RuntimeQuantityValue{eos::thermodynamicQuantityId<eos::quantity::Pressure>, 0.04}
+    };
+
+    const std::array<eos::RuntimeQuantityValue, 0> noInputs{};
+
+    const auto unsupportedOutput =
+        view.tryEvaluate(temperature, std::span<const eos::RuntimeQuantityValue>{densityInput});
+    REQUIRE_FALSE(unsupportedOutput.has_value());
+    CHECK(unsupportedOutput.error().code() == eos::EvaluationErrorCode::unsupported_relation);
+
+    const auto wrongInputCount = view.tryEvaluate(
+        eos::thermodynamicQuantityId<eos::quantity::Pressure>, std::span<const eos::RuntimeQuantityValue>{noInputs}
+    );
+    REQUIRE_FALSE(wrongInputCount.has_value());
+    CHECK(wrongInputCount.error().code() == eos::EvaluationErrorCode::wrong_input_count);
+
+    const auto wrongInputQuantity = view.tryEvaluate(
+        eos::thermodynamicQuantityId<eos::quantity::Density>, std::span<const eos::RuntimeQuantityValue>{pressureInput}
+    );
+    REQUIRE_FALSE(wrongInputQuantity.has_value());
+    CHECK(wrongInputQuantity.error().code() == eos::EvaluationErrorCode::wrong_input_quantity);
+
+    const auto unsupportedDerivative = view.tryPartialDerivative(
+        eos::thermodynamicQuantityId<eos::quantity::SpecificEnthalpy>,
+        eos::thermodynamicQuantityId<eos::quantity::Pressure>, std::span<const eos::RuntimeQuantityValue>{pressureInput}
+    );
+    REQUIRE_FALSE(unsupportedDerivative.has_value());
+    CHECK(unsupportedDerivative.error().code() == eos::EvaluationErrorCode::unsupported_derivative);
+
+    const auto invalidDensity = view.tryEvaluate<eos::quantity::Pressure>(eos::DensityValue{-0.1});
+    REQUIRE_FALSE(invalidDensity.has_value());
+    CHECK(invalidDensity.error().code() == eos::EvaluationErrorCode::outside_domain);
+
+    const auto nonfiniteDensity =
+        view.tryEvaluate<eos::quantity::Pressure>(eos::DensityValue{std::numeric_limits<double>::quiet_NaN()});
+    REQUIRE_FALSE(nonfiniteDensity.has_value());
+    CHECK(nonfiniteDensity.error().code() == eos::EvaluationErrorCode::nonfinite_input);
+}
+
+TEST_CASE(
+    "One Runtime EOS Function Accepts Heterogeneous Concrete Models",
+    tags::equation_of_state_runtime_compatibility
+) {
+    const eos::Polytrope polytrope(3.0, 0.25);
+    const LinearPressureEquationOfState linearEquationOfState;
+
+    const std::array views{eos::EquationOfStateView{polytrope}, eos::EquationOfStateView{linearEquationOfState}};
+
+    const eos::DensityValue density{0.7};
+
+    const auto polytropicPressure = pressureAtDensity(views[0], density);
+    const auto linearPressure     = pressureAtDensity(views[1], density);
+
+    REQUIRE(polytropicPressure.has_value());
+    REQUIRE(linearPressure.has_value());
+
+    CHECK(polytropicPressure->value() == eos::evaluate<eos::quantity::Pressure>(polytrope, density).value());
+    CHECK(linearPressure->value() == 1.9);
+}
+
+TEST_CASE(
+    "Runtime EOS View Remains Valid When Stable Ownership Moves",
+    tags::equation_of_state_runtime_contract
+) {
+    auto owner = std::make_unique<const eos::Polytrope>(3.0, 0.25);
+    const eos::EquationOfStateView view{*owner};
+
+    auto movedOwner     = std::move(owner);
+
+    const auto pressure = view.tryEvaluate<eos::quantity::Pressure>(eos::DensityValue{0.7});
+
+    REQUIRE(movedOwner != nullptr);
+    REQUIRE(pressure.has_value());
+    CHECK(pressure->value() == eos::evaluate<eos::quantity::Pressure>(*movedOwner, eos::DensityValue{0.7}).value());
+}

tests/physics/equation_of_state_type_system.cpp

@@ -0,0 +1,228 @@
+#include <concepts>
+#include <string_view>
+#include <type_traits>
+
+#include <catch2/catch_test_macros.hpp>
+
+import mean_field;
+import test_helpers;
+
+namespace {
+    namespace eos = mean_field::eos;
+
+    struct Entropy final : eos::ThermodynamicQuantity { };
+    struct ElectronFraction final : eos::ThermodynamicQuantity { };
+
+    using SpecificEnthalpyFromPressureAndEntropy =
+        eos::Relation<eos::quantity::SpecificEnthalpy, eos::quantity::Pressure, Entropy>;
+
+    class CompleteEquationOfState final {
+    public:
+        using Relations = eos::RelationCatalog<
+            eos::PressureFromDensity,
+            eos::SpecificEnthalpyFromPressure,
+            SpecificEnthalpyFromPressureAndEntropy>;
+
+        [[nodiscard]] constexpr eos::PressureValue evaluate(
+            eos::PressureFromDensity,
+            const eos::DensityValue density
+        ) const noexcept {
+            return eos::PressureValue{2.0 * density.value()};
+        }
+
+        [[nodiscard]] constexpr eos::SpecificEnthalpyValue evaluate(
+            eos::SpecificEnthalpyFromPressure,
+            const eos::PressureValue pressure
+        ) const noexcept {
+            return eos::SpecificEnthalpyValue{3.0 * pressure.value()};
+        }
+
+        [[nodiscard]] constexpr eos::SpecificEnthalpyValue evaluate(
+            SpecificEnthalpyFromPressureAndEntropy,
+            const eos::PressureValue pressure,
+            const eos::QuantityValue<Entropy> entropy
+        ) const noexcept {
+            return eos::SpecificEnthalpyValue{3.0 * pressure.value() + 5.0 * entropy.value()};
+        }
+
+        [[nodiscard]] constexpr eos::PartialDerivative<
+            eos::quantity::SpecificEnthalpy,
+            Entropy>
+        partialDerivative(
+            SpecificEnthalpyFromPressureAndEntropy,
+            eos::WithRespectTo<Entropy>,
+            eos::PressureValue,
+            eos::QuantityValue<Entropy>
+        ) const noexcept {
+            return eos::PartialDerivative<eos::quantity::SpecificEnthalpy, Entropy>{5.0};
+        }
+    };
+
+    class MissingRelationImplementation final {
+    public:
+        using Relations = eos::RelationCatalog<eos::PressureFromDensity, eos::SpecificEnthalpyFromPressure>;
+
+        [[nodiscard]] eos::PressureValue evaluate(
+            eos::PressureFromDensity,
+            eos::DensityValue density
+        ) const {
+            return eos::PressureValue{density.value()};
+        }
+    };
+
+    class IncorrectRelationOutput final {
+    public:
+        using Relations = eos::RelationCatalog<eos::PressureFromDensity>;
+
+        [[nodiscard]] eos::DensityValue evaluate(
+            eos::PressureFromDensity,
+            eos::DensityValue density
+        ) const {
+            return density;
+        }
+    };
+
+    class InvalidRelationCatalog final {
+    public:
+        using Relations = eos::RelationCatalog<eos::Relation<double, eos::quantity::Density>>;
+    };
+
+    template <typename EquationOfState>
+    concept CanEvaluateDensityFromSpecificEnthalpy = requires(const EquationOfState &equationOfState) {
+        eos::evaluate<eos::quantity::Density>(equationOfState, eos::SpecificEnthalpyValue{1.0});
+    };
+} // namespace
+
+TEST_CASE(
+    "Thermodynamic Values Preserve Physical Quantity Types",
+    tags::equation_of_state_quantity_types
+) {
+    STATIC_CHECK(eos::ThermodynamicQuantityType<eos::quantity::Density>);
+    STATIC_CHECK(eos::ThermodynamicQuantityType<eos::quantity::Pressure>);
+    STATIC_CHECK(eos::ThermodynamicQuantityType<eos::quantity::SpecificEnthalpy>);
+    STATIC_CHECK_FALSE(eos::ThermodynamicQuantityType<const eos::quantity::Pressure>);
+
+    STATIC_CHECK_FALSE(std::same_as<eos::DensityValue, eos::PressureValue>);
+    STATIC_CHECK_FALSE(std::same_as<eos::PressureValue, eos::SpecificEnthalpyValue>);
+    STATIC_CHECK_FALSE(std::is_convertible_v<double, eos::PressureValue>);
+    STATIC_CHECK_FALSE(std::is_constructible_v<eos::PressureValue, eos::DensityValue>);
+
+    STATIC_CHECK(std::is_trivially_copyable_v<eos::DensityValue>);
+    STATIC_CHECK(std::is_standard_layout_v<eos::DensityValue>);
+    STATIC_CHECK(sizeof(eos::DensityValue) == sizeof(double));
+    STATIC_CHECK(sizeof(eos::PressureValue) == sizeof(double));
+    STATIC_CHECK(sizeof(eos::SpecificEnthalpyValue) == sizeof(double));
+    STATIC_CHECK(std::is_empty_v<eos::PressureFromDensity>);
+
+    constexpr eos::DensityValue density{-0.25};
+    STATIC_CHECK(density.value() == -0.25);
+}
+
+TEST_CASE(
+    "Thermodynamic Derivatives Preserve Numerator And Denominator Types",
+    tags::equation_of_state_quantity_types
+) {
+    using PressureByDensity          = eos::PartialDerivative<eos::quantity::Pressure, eos::quantity::Density>;
+
+    using PressureBySpecificEnthalpy = eos::PartialDerivative<eos::quantity::Pressure, eos::quantity::SpecificEnthalpy>;
+
+    STATIC_CHECK_FALSE(std::same_as<PressureByDensity, PressureBySpecificEnthalpy>);
+    STATIC_CHECK_FALSE(std::is_convertible_v<PressureByDensity, PressureBySpecificEnthalpy>);
+    STATIC_CHECK(std::is_trivially_copyable_v<PressureByDensity>);
+    STATIC_CHECK(std::is_standard_layout_v<PressureByDensity>);
+    STATIC_CHECK(sizeof(PressureByDensity) == sizeof(double));
+
+    constexpr PressureByDensity derivative{1.75};
+    STATIC_CHECK(derivative.value() == 1.75);
+}
+
+TEST_CASE(
+    "EOS Relation Catalog Rejects Invalid And Duplicate Relations",
+    tags::equation_of_state_relation_contract
+) {
+    using ValidCatalog     = eos::RelationCatalog<eos::PressureFromDensity, eos::SpecificEnthalpyFromPressure>;
+
+    using DuplicateCatalog = eos::RelationCatalog<eos::PressureFromDensity, eos::PressureFromDensity>;
+
+    using InvalidRelation  = eos::Relation<double, eos::quantity::Density>;
+    using InvalidCatalog   = eos::RelationCatalog<InvalidRelation>;
+    using RepeatedInputRelation =
+        eos::Relation<eos::quantity::Pressure, eos::quantity::Density, eos::quantity::Density>;
+    using RepeatedInputCatalog = eos::RelationCatalog<RepeatedInputRelation>;
+
+    STATIC_CHECK(eos::ValidRelationCatalog<ValidCatalog>);
+    STATIC_CHECK_FALSE(eos::ValidRelationCatalog<DuplicateCatalog>);
+    STATIC_CHECK_FALSE(eos::ValidRelationCatalog<InvalidCatalog>);
+    STATIC_CHECK_FALSE(eos::ValidRelationCatalog<RepeatedInputCatalog>);
+    STATIC_CHECK_FALSE(eos::ValidRelationCatalog<eos::RelationCatalog<>>);
+
+    STATIC_CHECK(eos::relationCatalogContains<ValidCatalog, eos::PressureFromDensity>);
+    STATIC_CHECK_FALSE(eos::relationCatalogContains<ValidCatalog, eos::DensityFromSpecificEnthalpy>);
+    STATIC_CHECK(eos::relationContainsInput<eos::PressureFromDensity, eos::quantity::Density>);
+    STATIC_CHECK_FALSE(eos::relationContainsInput<eos::PressureFromDensity, eos::quantity::Pressure>);
+
+    STATIC_CHECK(std::same_as<eos::RelationOutputT<eos::PressureFromDensity>, eos::quantity::Pressure>);
+    STATIC_CHECK(std::same_as<eos::RelationInputT<0, eos::PressureFromDensity>, eos::quantity::Density>);
+}
+
+TEST_CASE(
+    "EOS Model Contract Requires Every Declared Relation",
+    tags::equation_of_state_relation_contract
+) {
+    STATIC_CHECK(eos::EquationOfStateModel<CompleteEquationOfState>);
+    STATIC_CHECK_FALSE(eos::EquationOfStateModel<MissingRelationImplementation>);
+    STATIC_CHECK_FALSE(eos::EquationOfStateModel<IncorrectRelationOutput>);
+    STATIC_CHECK_FALSE(eos::EquationOfStateModel<InvalidRelationCatalog>);
+
+    STATIC_CHECK(eos::SupportsRelation<CompleteEquationOfState, eos::PressureFromDensity>);
+    STATIC_CHECK_FALSE(eos::SupportsRelation<CompleteEquationOfState, eos::DensityFromSpecificEnthalpy>);
+    STATIC_CHECK_FALSE(CanEvaluateDensityFromSpecificEnthalpy<CompleteEquationOfState>);
+    STATIC_CHECK(
+        eos::SupportsPartialDerivative<CompleteEquationOfState, SpecificEnthalpyFromPressureAndEntropy, Entropy>
+    );
+    STATIC_CHECK_FALSE(
+        eos::SupportsPartialDerivative<
+            CompleteEquationOfState, SpecificEnthalpyFromPressureAndEntropy, ElectronFraction>
+    );
+}
+
+TEST_CASE(
+    "EOS Evaluation Selects Relations From Typed Inputs",
+    tags::equation_of_state_relation_contract
+) {
+    constexpr CompleteEquationOfState equationOfState;
+
+    constexpr eos::PressureValue pressure =
+        eos::evaluate<eos::quantity::Pressure>(equationOfState, eos::DensityValue{1.25});
+
+    constexpr eos::SpecificEnthalpyValue specificEnthalpy = eos::evaluate<eos::quantity::SpecificEnthalpy>(
+        equationOfState, eos::PressureValue{0.5}, eos::QuantityValue<Entropy>{0.2}
+    );
+
+    constexpr auto entropyDerivative = eos::partialDerivative<eos::quantity::SpecificEnthalpy, Entropy>(
+        equationOfState, eos::PressureValue{0.5}, eos::QuantityValue<Entropy>{0.2}
+    );
+
+    STATIC_CHECK(noexcept(eos::evaluate<eos::quantity::Pressure>(equationOfState, eos::DensityValue{1.25})));
+    STATIC_CHECK(
+        noexcept(eos::partialDerivative<eos::quantity::SpecificEnthalpy, Entropy>(
+            equationOfState, eos::PressureValue{0.5}, eos::QuantityValue<Entropy>{0.2}
+        ))
+    );
+
+    STATIC_CHECK(pressure.value() == 2.5);
+    STATIC_CHECK(specificEnthalpy.value() == 2.5);
+    STATIC_CHECK(entropyDerivative.value() == 5.0);
+}
+
+TEST_CASE(
+    "EOS Evaluation Errors Retain A Structured Cause",
+    tags::equation_of_state_relation_contract
+) {
+    const eos::EvaluationError error(
+        eos::EvaluationErrorCode::outside_domain, "Density is outside the relation domain."
+    );
+
+    CHECK(error.code() == eos::EvaluationErrorCode::outside_domain);
+    CHECK(std::string_view{error.what()} == "Density is outside the relation domain.");
+}

tests/physics/polytropic_eos_characterization.cpp

@@ -0,0 +1,156 @@
+#include <array>
+#include <cmath>
+#include <limits>
+#include <stdexcept>
+
+#include <catch2/catch_test_macros.hpp>
+#include <catch2/matchers/catch_matchers_floating_point.hpp>
+
+import mean_field;
+import test_helpers;
+
+namespace eos = mean_field::eos;
+
+TEST_CASE(
+    "Polytropic EOS Pressure To Specific Enthalpy Relation Is Characterized",
+    tags::polytropic_eos_characterization
+) {
+    constexpr std::array<double, 3> polytropicIndices{1.0, 1.5, 3.0};
+    constexpr std::array<double, 3> polytropicConstants{0.25, 0.73, 2.0};
+    constexpr std::array<double, 5> pressures{0.0, 1.0e-12, 1.0e-4, 0.3, 5.0};
+
+    for (const double polytropicIndex : polytropicIndices) {
+        for (const double polytropicConstant : polytropicConstants) {
+            const mean_field::eos::Polytrope equationOfState(polytropicIndex, polytropicConstant);
+
+            for (const double pressure : pressures) {
+                CAPTURE(polytropicIndex, polytropicConstant, pressure);
+
+                const double indexPlusOne     = polytropicIndex + 1.0;
+                const double expectedEnthalpy = indexPlusOne *
+                                                std::pow(polytropicConstant, polytropicIndex / indexPlusOne) *
+                                                std::pow(pressure, 1.0 / indexPlusOne);
+
+                const double enthalpy =
+                    eos::evaluate<eos::quantity::SpecificEnthalpy>(equationOfState, eos::PressureValue{pressure})
+                        .value();
+
+                if (pressure == 0.0) {
+                    CHECK(enthalpy == 0.0);
+                } else {
+                    CHECK_THAT(enthalpy, Catch::Matchers::WithinRel(expectedEnthalpy, 5.0e-14));
+
+                    const double recoveredPressure =
+                        eos::evaluate<eos::quantity::Pressure>(equationOfState, eos::SpecificEnthalpyValue{enthalpy})
+                            .value();
+
+                    CHECK_THAT(recoveredPressure, Catch::Matchers::WithinRel(pressure, 5.0e-13));
+                }
+            }
+        }
+    }
+}
+
+TEST_CASE(
+    "Polytropic EOS Domain Contract Covers Every Relation",
+    tags::polytropic_eos_characterization
+) {
+    constexpr double infinity = std::numeric_limits<double>::infinity();
+    constexpr double quietNaN = std::numeric_limits<double>::quiet_NaN();
+
+    for (const double invalidIndex : std::array<double, 4>{0.999, infinity, -infinity, quietNaN}) {
+        CAPTURE(invalidIndex);
+        CHECK_THROWS_AS(mean_field::eos::Polytrope(invalidIndex, 1.0), std::invalid_argument);
+    }
+
+    for (const double invalidConstant : std::array<double, 5>{0.0, -0.1, infinity, -infinity, quietNaN}) {
+        CAPTURE(invalidConstant);
+        CHECK_THROWS_AS(mean_field::eos::Polytrope(3.0, invalidConstant), std::invalid_argument);
+    }
+
+    const mean_field::eos::Polytrope equationOfState(3.0, 0.75);
+
+    constexpr double negativeDensity = -0.1;
+    CHECK_THROWS_AS(
+        eos::evaluate<eos::quantity::Pressure>(equationOfState, eos::DensityValue{negativeDensity}), std::domain_error
+    );
+    CHECK_THROWS_AS(
+        eos::evaluate<eos::quantity::SpecificEnthalpy>(equationOfState, eos::DensityValue{negativeDensity}),
+        std::domain_error
+    );
+    CHECK_THROWS_AS(
+        (eos::partialDerivative<eos::quantity::Pressure, eos::quantity::Density>(
+            equationOfState, eos::DensityValue{negativeDensity}
+        )),
+        std::domain_error
+    );
+
+    CHECK_THROWS_AS(
+        eos::evaluate<eos::quantity::SpecificEnthalpy>(equationOfState, eos::PressureValue{-0.1}), std::domain_error
+    );
+
+    constexpr double exteriorEnthalpy = -0.1;
+    CHECK(
+        eos::evaluate<eos::quantity::Density>(equationOfState, eos::SpecificEnthalpyValue{exteriorEnthalpy}).value() ==
+        0.0
+    );
+    CHECK(
+        eos::evaluate<eos::quantity::Pressure>(equationOfState, eos::SpecificEnthalpyValue{exteriorEnthalpy}).value() ==
+        0.0
+    );
+    CHECK(
+        (eos::partialDerivative<eos::quantity::Density, eos::quantity::SpecificEnthalpy>(
+             equationOfState, eos::SpecificEnthalpyValue{exteriorEnthalpy}
+         )
+             .value() == 0.0)
+    );
+    CHECK(
+        (eos::partialDerivative<eos::quantity::Pressure, eos::quantity::SpecificEnthalpy>(
+             equationOfState, eos::SpecificEnthalpyValue{exteriorEnthalpy}
+         )
+             .value() == 0.0)
+    );
+
+    for (const double nonfiniteValue : std::array<double, 3>{infinity, -infinity, quietNaN}) {
+        CAPTURE(nonfiniteValue);
+
+        CHECK_THROWS_AS(
+            eos::evaluate<eos::quantity::Pressure>(equationOfState, eos::DensityValue{nonfiniteValue}),
+            std::domain_error
+        );
+        CHECK_THROWS_AS(
+            eos::evaluate<eos::quantity::SpecificEnthalpy>(equationOfState, eos::DensityValue{nonfiniteValue}),
+            std::domain_error
+        );
+        CHECK_THROWS_AS(
+            (eos::partialDerivative<eos::quantity::Pressure, eos::quantity::Density>(
+                equationOfState, eos::DensityValue{nonfiniteValue}
+            )),
+            std::domain_error
+        );
+        CHECK_THROWS_AS(
+            eos::evaluate<eos::quantity::SpecificEnthalpy>(equationOfState, eos::PressureValue{nonfiniteValue}),
+            std::domain_error
+        );
+        CHECK_THROWS_AS(
+            eos::evaluate<eos::quantity::Density>(equationOfState, eos::SpecificEnthalpyValue{nonfiniteValue}),
+            std::domain_error
+        );
+        CHECK_THROWS_AS(
+            eos::evaluate<eos::quantity::Pressure>(equationOfState, eos::SpecificEnthalpyValue{nonfiniteValue}),
+            std::domain_error
+        );
+        CHECK_THROWS_AS(
+            (eos::partialDerivative<eos::quantity::Density, eos::quantity::SpecificEnthalpy>(
+                equationOfState, eos::SpecificEnthalpyValue{nonfiniteValue}
+            )),
+            std::domain_error
+        );
+        CHECK_THROWS_AS(
+            (eos::partialDerivative<eos::quantity::Pressure, eos::quantity::SpecificEnthalpy>(
+                equationOfState, eos::SpecificEnthalpyValue{nonfiniteValue}
+            )),
+            std::domain_error
+        );
+    }
+}

tests/physics/polytropic_eos_relations.cpp

@@ -0,0 +1,200 @@
+#include <array>
+#include <cmath>
+#include <concepts>
+#include <limits>
+#include <type_traits>
+
+#include <catch2/catch_test_macros.hpp>
+#include <catch2/matchers/catch_matchers_floating_point.hpp>
+
+import mean_field;
+import test_helpers;
+
+namespace {
+    namespace eos = mean_field::eos;
+
+    template <typename Candidate>
+    concept HasAnyUnaryEquationOfStateConversion =
+        requires(const Candidate &candidate, const double value) { candidate.pressure_from_density(value); } ||
+        requires(const Candidate &candidate, const double value) { candidate.pressure_from_enthalpy(value); } ||
+        requires(const Candidate &candidate, const double value) { candidate.enthalpy_from_density(value); } ||
+        requires(const Candidate &candidate, const double value) { candidate.enthalpy_from_pressure(value); } ||
+        requires(const Candidate &candidate, const double value) { candidate.density_from_enthalpy(value); } ||
+        requires(const Candidate &candidate, const double value) {
+            candidate.density_derivative_from_enthalpy(value);
+        } ||
+        requires(const Candidate &candidate, const double value) {
+            candidate.pressure_derivative_from_enthalpy(value);
+        } ||
+        requires(const Candidate &candidate, const double value) { candidate.pressure_derivative_from_density(value); };
+} // namespace
+
+TEST_CASE(
+    "Polytropic EOS Declares Its Thermodynamic Relation Contract",
+    tags::polytropic_eos_relation_contract
+) {
+    using Polytrope = eos::Polytrope;
+
+    STATIC_CHECK(eos::EquationOfStateModel<Polytrope>);
+    STATIC_CHECK_FALSE(std::is_polymorphic_v<Polytrope>);
+    STATIC_CHECK_FALSE(HasAnyUnaryEquationOfStateConversion<Polytrope>);
+    STATIC_CHECK(Polytrope::Relations::size == 5);
+
+    STATIC_CHECK(eos::SupportsRelation<Polytrope, eos::PressureFromDensity>);
+    STATIC_CHECK(eos::SupportsRelation<Polytrope, eos::PressureFromSpecificEnthalpy>);
+    STATIC_CHECK(eos::SupportsRelation<Polytrope, eos::SpecificEnthalpyFromDensity>);
+    STATIC_CHECK(eos::SupportsRelation<Polytrope, eos::SpecificEnthalpyFromPressure>);
+    STATIC_CHECK(eos::SupportsRelation<Polytrope, eos::DensityFromSpecificEnthalpy>);
+
+    STATIC_CHECK(eos::SupportsPartialDerivative<Polytrope, eos::PressureFromDensity, eos::quantity::Density>);
+    STATIC_CHECK(
+        eos::SupportsPartialDerivative<Polytrope, eos::PressureFromSpecificEnthalpy, eos::quantity::SpecificEnthalpy>
+    );
+    STATIC_CHECK(
+        eos::SupportsPartialDerivative<Polytrope, eos::DensityFromSpecificEnthalpy, eos::quantity::SpecificEnthalpy>
+    );
+
+    STATIC_CHECK_FALSE(
+        eos::SupportsPartialDerivative<Polytrope, eos::SpecificEnthalpyFromPressure, eos::quantity::Pressure>
+    );
+    STATIC_CHECK_FALSE(
+        eos::SupportsPartialDerivative<Polytrope, eos::SpecificEnthalpyFromDensity, eos::quantity::Density>
+    );
+}
+
+TEST_CASE(
+    "Polytropic EOS Typed Relations Preserve Analytic Values",
+    tags::polytropic_eos_characterization
+) {
+    constexpr std::array<double, 3> polytropicIndices{1.0, 1.5, 3.0};
+    constexpr std::array<double, 2> polytropicConstants{0.25, 0.73};
+    constexpr std::array<double, 4> densities{0.0, 1.0e-6, 0.2, 2.0};
+    constexpr std::array<double, 4> specificEnthalpies{-0.3, 0.0, 0.2, 1.7};
+    constexpr std::array<double, 4> pressures{0.0, 1.0e-8, 0.3, 4.0};
+
+    for (const double polytropicIndex : polytropicIndices) {
+        for (const double polytropicConstant : polytropicConstants) {
+            const eos::Polytrope equationOfState(polytropicIndex, polytropicConstant);
+
+            for (const double density : densities) {
+                CAPTURE(polytropicIndex, polytropicConstant, density);
+
+                const double expectedPressure = polytropicConstant * std::pow(density, 1.0 + 1.0 / polytropicIndex);
+                const double expectedSpecificEnthalpy =
+                    (polytropicIndex + 1.0) * polytropicConstant * std::pow(density, 1.0 / polytropicIndex);
+
+                CHECK(
+                    eos::evaluate<eos::quantity::Pressure>(equationOfState, eos::DensityValue{density}).value() ==
+                    expectedPressure
+                );
+
+                CHECK(
+                    eos::evaluate<eos::quantity::SpecificEnthalpy>(equationOfState, eos::DensityValue{density})
+                        .value() == expectedSpecificEnthalpy
+                );
+
+                CHECK_THAT(
+                    (eos::partialDerivative<eos::quantity::Pressure, eos::quantity::Density>(
+                         equationOfState, eos::DensityValue{density}
+                    )
+                         .value()),
+                    Catch::Matchers::WithinRel(
+                        density == 0.0 ? 0.0 : expectedSpecificEnthalpy / polytropicIndex, 2.0e-15
+                    )
+                );
+            }
+
+            for (const double specificEnthalpy : specificEnthalpies) {
+                CAPTURE(polytropicIndex, polytropicConstant, specificEnthalpy);
+
+                const double expectedDensity =
+                    specificEnthalpy <= 0.0
+                        ? 0.0
+                        : std::pow(specificEnthalpy / ((polytropicIndex + 1.0) * polytropicConstant), polytropicIndex);
+
+                CHECK(
+                    eos::evaluate<eos::quantity::Density>(equationOfState, eos::SpecificEnthalpyValue{specificEnthalpy})
+                        .value() == expectedDensity
+                );
+
+                CHECK(
+                    eos::evaluate<eos::quantity::Pressure>(
+                        equationOfState, eos::SpecificEnthalpyValue{specificEnthalpy}
+                    )
+                        .value() ==
+                    (specificEnthalpy <= 0.0 ? 0.0 : expectedDensity * specificEnthalpy / (polytropicIndex + 1.0))
+                );
+
+                CHECK(
+                    (eos::partialDerivative<eos::quantity::Pressure, eos::quantity::SpecificEnthalpy>(
+                         equationOfState, eos::SpecificEnthalpyValue{specificEnthalpy}
+                     )
+                         .value() == expectedDensity)
+                );
+            }
+
+            for (const double pressure : pressures) {
+                CAPTURE(polytropicIndex, polytropicConstant, pressure);
+
+                const double indexPlusOne             = polytropicIndex + 1.0;
+                const double expectedSpecificEnthalpy = indexPlusOne *
+                                                        std::pow(polytropicConstant, polytropicIndex / indexPlusOne) *
+                                                        std::pow(pressure, 1.0 / indexPlusOne);
+
+                CHECK(
+                    eos::evaluate<eos::quantity::SpecificEnthalpy>(equationOfState, eos::PressureValue{pressure})
+                        .value() == expectedSpecificEnthalpy
+                );
+            }
+        }
+    }
+}
+
+TEST_CASE(
+    "Typed Polytropic EOS Preserves Domain And Exterior Semantics",
+    tags::polytropic_eos_relation_contract
+) {
+    const eos::Polytrope equationOfState(3.0, 0.75);
+
+    try {
+        static_cast<void>(eos::evaluate<eos::quantity::Pressure>(equationOfState, eos::DensityValue{-0.1}));
+        FAIL("A negative density must be rejected.");
+    } catch (const eos::EvaluationError &error) {
+        CHECK(error.code() == eos::EvaluationErrorCode::outside_domain);
+    }
+
+    try {
+        static_cast<void>(eos::evaluate<eos::quantity::SpecificEnthalpy>(
+            equationOfState, eos::PressureValue{std::numeric_limits<double>::quiet_NaN()}
+        ));
+        FAIL("A nonfinite pressure must be rejected.");
+    } catch (const eos::EvaluationError &error) {
+        CHECK(error.code() == eos::EvaluationErrorCode::nonfinite_input);
+    }
+
+    constexpr double exteriorSpecificEnthalpy = -0.3;
+
+    CHECK(
+        eos::evaluate<eos::quantity::Density>(equationOfState, eos::SpecificEnthalpyValue{exteriorSpecificEnthalpy})
+            .value() == 0.0
+    );
+
+    CHECK(
+        eos::evaluate<eos::quantity::Pressure>(equationOfState, eos::SpecificEnthalpyValue{exteriorSpecificEnthalpy})
+            .value() == 0.0
+    );
+
+    CHECK(
+        (eos::partialDerivative<eos::quantity::Density, eos::quantity::SpecificEnthalpy>(
+             equationOfState, eos::SpecificEnthalpyValue{exteriorSpecificEnthalpy}
+         )
+             .value() == 0.0)
+    );
+
+    CHECK(
+        (eos::partialDerivative<eos::quantity::Pressure, eos::quantity::SpecificEnthalpy>(
+             equationOfState, eos::SpecificEnthalpyValue{exteriorSpecificEnthalpy}
+         )
+             .value() == 0.0)
+    );
+}

tests/surface/constant_surface_compilation.cpp

@@ -0,0 +1,329 @@
+#include <cmath>
+#include <concepts>
+#include <limits>
+#include <string_view>
+#include <type_traits>
+
+#include <catch2/catch_test_macros.hpp>
+#include <catch2/matchers/catch_matchers_floating_point.hpp>
+
+import mean_field;
+import test_helpers;
+
+namespace {
+    namespace eos     = mean_field::eos;
+    namespace field   = mean_field::field;
+    namespace surface = mean_field::surface;
+
+    struct Entropy final : eos::ThermodynamicQuantity {
+        static constexpr std::string_view identifier = "entropy";
+    };
+
+    struct ElectronFraction final : eos::ThermodynamicQuantity {
+        static constexpr std::string_view identifier = "electron_fraction";
+    };
+
+    struct EntropyField final {
+        static constexpr std::string_view name = "entropy";
+    };
+
+    struct ElectronFractionField final {
+        static constexpr std::string_view name = "electron_fraction";
+    };
+
+    using SpecificEnthalpyFromPressureEntropyAndElectronFraction =
+        eos::Relation<eos::quantity::SpecificEnthalpy, eos::quantity::Pressure, Entropy, ElectronFraction>;
+
+    class GeneralStellarMatterEquationOfState final {
+    public:
+        using Relations = eos::RelationCatalog<SpecificEnthalpyFromPressureEntropyAndElectronFraction>;
+
+        [[nodiscard]] constexpr eos::SpecificEnthalpyValue evaluate(
+            SpecificEnthalpyFromPressureEntropyAndElectronFraction,
+            const eos::PressureValue pressure,
+            const eos::QuantityValue<Entropy> entropy,
+            const eos::QuantityValue<ElectronFraction> electronFraction
+        ) const noexcept {
+            return eos::SpecificEnthalpyValue{
+                2.0 * pressure.value() + 3.0 * entropy.value() + 5.0 * electronFraction.value()
+            };
+        }
+
+        [[nodiscard]] constexpr eos::PartialDerivative<
+            eos::quantity::SpecificEnthalpy,
+            Entropy>
+        partialDerivative(
+            SpecificEnthalpyFromPressureEntropyAndElectronFraction,
+            eos::WithRespectTo<Entropy>,
+            eos::PressureValue,
+            eos::QuantityValue<Entropy>,
+            eos::QuantityValue<ElectronFraction>
+        ) const noexcept {
+            return eos::PartialDerivative<eos::quantity::SpecificEnthalpy, Entropy>{3.0};
+        }
+
+        [[nodiscard]] constexpr eos::PartialDerivative<
+            eos::quantity::SpecificEnthalpy,
+            ElectronFraction>
+        partialDerivative(
+            SpecificEnthalpyFromPressureEntropyAndElectronFraction,
+            eos::WithRespectTo<ElectronFraction>,
+            eos::PressureValue,
+            eos::QuantityValue<Entropy>,
+            eos::QuantityValue<ElectronFraction>
+        ) const noexcept {
+            return eos::PartialDerivative<eos::quantity::SpecificEnthalpy, ElectronFraction>{5.0};
+        }
+    };
+
+    class GeneralEquationOfStateWithoutElectronFractionPartial final {
+    public:
+        using Relations = eos::RelationCatalog<SpecificEnthalpyFromPressureEntropyAndElectronFraction>;
+
+        [[nodiscard]] constexpr eos::SpecificEnthalpyValue evaluate(
+            SpecificEnthalpyFromPressureEntropyAndElectronFraction,
+            const eos::PressureValue pressure,
+            const eos::QuantityValue<Entropy> entropy,
+            const eos::QuantityValue<ElectronFraction> electronFraction
+        ) const noexcept {
+            return eos::SpecificEnthalpyValue{pressure.value() + entropy.value() + electronFraction.value()};
+        }
+
+        [[nodiscard]] constexpr eos::PartialDerivative<
+            eos::quantity::SpecificEnthalpy,
+            Entropy>
+        partialDerivative(
+            SpecificEnthalpyFromPressureEntropyAndElectronFraction,
+            eos::WithRespectTo<Entropy>,
+            eos::PressureValue,
+            eos::QuantityValue<Entropy>,
+            eos::QuantityValue<ElectronFraction>
+        ) const noexcept {
+            return eos::PartialDerivative<eos::quantity::SpecificEnthalpy, Entropy>{1.0};
+        }
+    };
+
+    using SpecificEnthalpyFromPressureAndEntropy =
+        eos::Relation<eos::quantity::SpecificEnthalpy, eos::quantity::Pressure, Entropy>;
+
+    class AmbiguousSurfaceEquationOfState final {
+    public:
+        using Relations =
+            eos::RelationCatalog<eos::SpecificEnthalpyFromPressure, SpecificEnthalpyFromPressureAndEntropy>;
+
+        [[nodiscard]] constexpr eos::SpecificEnthalpyValue evaluate(
+            eos::SpecificEnthalpyFromPressure,
+            const eos::PressureValue pressure
+        ) const noexcept {
+            return eos::SpecificEnthalpyValue{pressure.value()};
+        }
+
+        [[nodiscard]] constexpr eos::SpecificEnthalpyValue evaluate(
+            SpecificEnthalpyFromPressureAndEntropy,
+            const eos::PressureValue pressure,
+            const eos::QuantityValue<Entropy> entropy
+        ) const noexcept {
+            return eos::SpecificEnthalpyValue{pressure.value() + entropy.value()};
+        }
+
+        [[nodiscard]] constexpr eos::PartialDerivative<
+            eos::quantity::SpecificEnthalpy,
+            Entropy>
+        partialDerivative(
+            SpecificEnthalpyFromPressureAndEntropy,
+            eos::WithRespectTo<Entropy>,
+            eos::PressureValue,
+            eos::QuantityValue<Entropy>
+        ) const noexcept {
+            return eos::PartialDerivative<eos::quantity::SpecificEnthalpy, Entropy>{1.0};
+        }
+    };
+
+    class DensityOnlyEquationOfState final {
+    public:
+        using Relations = eos::RelationCatalog<eos::PressureFromDensity>;
+
+        [[nodiscard]] constexpr eos::PressureValue evaluate(
+            eos::PressureFromDensity,
+            const eos::DensityValue density
+        ) const noexcept {
+            return eos::PressureValue{density.value()};
+        }
+    };
+
+    using GeneralSurfaceFormulation = surface::SurfaceConstraintFormulation<
+        eos::quantity::SpecificEnthalpy,
+        field::Enthalpy,
+        surface::SurfaceStateBindings<
+            surface::SurfaceStateBinding<eos::quantity::SpecificEnthalpy, field::Enthalpy>,
+            surface::SurfaceStateBinding<Entropy, EntropyField>,
+            surface::SurfaceStateBinding<ElectronFraction, ElectronFractionField>>>;
+
+    struct PolytropicSurfaceState final {
+        double specificEnthalpy;
+
+        [[nodiscard]] eos::SpecificEnthalpyValue value(eos::quantity::SpecificEnthalpy) const noexcept {
+            return eos::SpecificEnthalpyValue{specificEnthalpy};
+        }
+    };
+
+    struct GeneralSurfaceState final {
+        double specificEnthalpy;
+        double entropy;
+        double electronFraction;
+
+        [[nodiscard]] eos::SpecificEnthalpyValue value(eos::quantity::SpecificEnthalpy) const noexcept {
+            return eos::SpecificEnthalpyValue{specificEnthalpy};
+        }
+
+        [[nodiscard]] eos::QuantityValue<Entropy> value(Entropy) const noexcept {
+            return eos::QuantityValue<Entropy>{entropy};
+        }
+
+        [[nodiscard]] eos::QuantityValue<ElectronFraction> value(ElectronFraction) const noexcept {
+            return eos::QuantityValue<ElectronFraction>{electronFraction};
+        }
+    };
+
+    template <typename Candidate>
+    concept HasTargetEnthalpy = requires(const Candidate &candidate) { candidate.targetEnthalpy; };
+} // namespace
+
+TEST_CASE(
+    "Constant Pressure Surface Prescribes Only A Pressure Quantity",
+    tags::surface_prescription_type_contract
+) {
+    STATIC_CHECK(std::same_as<surface::ConstantPressureSurface::PhysicalQuantity, eos::quantity::Pressure>);
+    STATIC_CHECK(std::constructible_from<surface::ConstantPressureSurface, eos::PressureValue>);
+    STATIC_CHECK_FALSE(std::constructible_from<surface::ConstantPressureSurface, eos::SpecificEnthalpyValue>);
+    STATIC_CHECK_FALSE(std::constructible_from<surface::ConstantPressureSurface, double>);
+    STATIC_CHECK(std::same_as<surface::Isobaric, surface::ConstantPressureSurface>);
+    STATIC_CHECK(std::is_trivially_copyable_v<surface::ConstantPressureSurface>);
+    STATIC_CHECK(std::is_trivially_copyable_v<surface::PressureSurfaceDescriptor>);
+    STATIC_CHECK(std::is_trivially_copyable_v<surface::RuntimeSurfaceConstraintDependencies>);
+
+    const surface::ConstantPressureSurface pressureSurface{eos::PressureValue{0.03125}};
+
+    CHECK(pressureSurface.targetPressure() == eos::PressureValue{0.03125});
+    CHECK(pressureSurface.descriptor().targetPressure == 0.03125);
+
+    CHECK_THROWS_AS(surface::ConstantPressureSurface{eos::PressureValue{-0.1}}, std::invalid_argument);
+    CHECK_THROWS_AS(
+        surface::ConstantPressureSurface{eos::PressureValue{std::numeric_limits<double>::infinity()}},
+        std::invalid_argument
+    );
+}
+
+TEST_CASE(
+    "Polytropic EOS Resolves Constant Surface Pressure Through Its Enthalpy Relation",
+    tags::surface_constraint_compilation
+) {
+    using Formulation = surface::BarotropicSurfaceFormulation;
+
+    STATIC_CHECK(surface::PressureSurfaceCompilable<Formulation, eos::Polytrope>);
+    STATIC_CHECK_FALSE(surface::PressureSurfaceCompilable<Formulation, DensityOnlyEquationOfState>);
+
+    const eos::Polytrope equationOfState(3.0, 0.25);
+    const surface::ConstantPressureSurface pressureSurface{eos::PressureValue{0.03125}};
+    const auto constraint = surface::compilePressureSurfaceConstraint<Formulation>(pressureSurface, equationOfState);
+
+    using Constraint      = std::remove_cvref_t<decltype(constraint)>;
+    using Dependencies    = Constraint::SurfaceDependencies;
+
+    STATIC_CHECK(std::is_trivially_copyable_v<Constraint>);
+    STATIC_CHECK(std::same_as<Constraint::Relation, eos::SpecificEnthalpyFromPressure>);
+    STATIC_CHECK(std::same_as<Dependencies::RowField, field::Enthalpy>);
+    STATIC_CHECK(std::same_as<Dependencies::StateFieldTypes, field::TypeList<field::Enthalpy>>);
+    STATIC_CHECK_FALSE(HasTargetEnthalpy<Constraint>);
+
+    const double requiredSpecificEnthalpy =
+        eos::evaluate<eos::quantity::SpecificEnthalpy>(equationOfState, pressureSurface.targetPressure()).value();
+    const PolytropicSurfaceState state{requiredSpecificEnthalpy};
+    const PolytropicSurfaceState variation{-0.19};
+
+    CHECK(constraint.targetPressure() == eos::PressureValue{0.03125});
+    CHECK(constraint.residual(state) == 0.0);
+    CHECK(constraint.jacobianAction(state, variation) == -0.19);
+
+    const auto runtimeDependencies = constraint.runtimeDependencies();
+    REQUIRE(runtimeDependencies.stateFields.size() == 1);
+    CHECK(runtimeDependencies.residualRowField == surface::surfaceFieldId<field::Enthalpy>);
+    CHECK(runtimeDependencies.stateFields[0] == surface::surfaceFieldId<field::Enthalpy>);
+}
+
+TEST_CASE(
+    "General EOS Resolves Constant Surface Pressure With Local Composition",
+    tags::surface_constraint_compilation
+) {
+    STATIC_CHECK(surface::PressureSurfaceCompilable<GeneralSurfaceFormulation, GeneralStellarMatterEquationOfState>);
+    STATIC_CHECK_FALSE(
+        surface::PressureSurfaceCompilable<surface::BarotropicSurfaceFormulation, GeneralStellarMatterEquationOfState>
+    );
+    STATIC_CHECK_FALSE(
+        surface::PressureSurfaceCompilable<
+            GeneralSurfaceFormulation, GeneralEquationOfStateWithoutElectronFractionPartial>
+    );
+    STATIC_CHECK_FALSE(surface::PressureSurfaceCompilable<GeneralSurfaceFormulation, AmbiguousSurfaceEquationOfState>);
+
+    const GeneralStellarMatterEquationOfState equationOfState;
+    const surface::ConstantPressureSurface pressureSurface{eos::PressureValue{0.4}};
+    const auto constraint =
+        surface::compilePressureSurfaceConstraint<GeneralSurfaceFormulation>(pressureSurface, equationOfState);
+
+    using Constraint   = std::remove_cvref_t<decltype(constraint)>;
+    using Dependencies = Constraint::SurfaceDependencies;
+
+    STATIC_CHECK(std::same_as<Constraint::Relation, SpecificEnthalpyFromPressureEntropyAndElectronFraction>);
+    STATIC_CHECK(
+        std::same_as<
+            Dependencies::StateFieldTypes, field::TypeList<field::Enthalpy, EntropyField, ElectronFractionField>>
+    );
+
+    constexpr GeneralSurfaceState firstSurface{
+        .specificEnthalpy = 2.0 * 0.4 + 3.0 * 0.2 + 5.0 * 0.1, .entropy = 0.2, .electronFraction = 0.1
+    };
+    constexpr GeneralSurfaceState secondSurface{
+        .specificEnthalpy = 2.0 * 0.4 + 3.0 * 0.3 + 5.0 * 0.1, .entropy = 0.3, .electronFraction = 0.1
+    };
+
+    CHECK(firstSurface.specificEnthalpy != secondSurface.specificEnthalpy);
+    CHECK(constraint.residual(firstSurface) == 0.0);
+    CHECK(constraint.residual(secondSurface) == 0.0);
+
+    const auto runtimeDependencies = constraint.runtimeDependencies();
+    REQUIRE(runtimeDependencies.stateFields.size() == 3);
+    CHECK(runtimeDependencies.stateFields[0] == surface::surfaceFieldId<field::Enthalpy>);
+    CHECK(runtimeDependencies.stateFields[1] == surface::surfaceFieldId<EntropyField>);
+    CHECK(runtimeDependencies.stateFields[2] == surface::surfaceFieldId<ElectronFractionField>);
+}
+
+TEST_CASE(
+    "General EOS Pressure Surface Jacobian Includes Every Local State Dependency",
+    tags::surface_constraint_jacobian
+) {
+    const GeneralStellarMatterEquationOfState equationOfState;
+    const surface::ConstantPressureSurface pressureSurface{eos::PressureValue{0.4}};
+    const auto constraint =
+        surface::compilePressureSurfaceConstraint<GeneralSurfaceFormulation>(pressureSurface, equationOfState);
+
+    constexpr GeneralSurfaceState state{.specificEnthalpy = 1.7, .entropy = 0.2, .electronFraction = 0.1};
+    constexpr GeneralSurfaceState variation{.specificEnthalpy = 0.7, .entropy = -0.2, .electronFraction = 0.05};
+    constexpr double step = 1.0e-7;
+
+    const GeneralSurfaceState forward{
+        .specificEnthalpy = state.specificEnthalpy + step * variation.specificEnthalpy,
+        .entropy          = state.entropy + step * variation.entropy,
+        .electronFraction = state.electronFraction + step * variation.electronFraction
+    };
+    const GeneralSurfaceState backward{
+        .specificEnthalpy = state.specificEnthalpy - step * variation.specificEnthalpy,
+        .entropy          = state.entropy - step * variation.entropy,
+        .electronFraction = state.electronFraction - step * variation.electronFraction
+    };
+
+    const double finiteDifference = (constraint.residual(forward) - constraint.residual(backward)) / (2.0 * step);
+    const double jacobianAction   = constraint.jacobianAction(state, variation);
+
+    CHECK(jacobianAction == variation.specificEnthalpy - 3.0 * variation.entropy - 5.0 * variation.electronFraction);
+    CHECK_THAT(finiteDifference, Catch::Matchers::WithinAbs(jacobianAction, 2.0e-9));
+}

tests/surface/isobaric.cpp

@@ -1,76 +0,0 @@
-#include <cmath>
-#include <limits>
-#include <stdexcept>
-
-#include <catch2/catch_test_macros.hpp>
-
-import mean_field;
-import test_helpers;
-
-TEST_CASE(
-    "Isobaric Surface Resolves Zero Pressure To Zero Enthalpy",
-    tags::barotrope &tags::unit &tags::surface
-) {
-    const mean_field::eos::Polytrope equationOfState(3.0, 0.25);
-
-    const mean_field::surface::Isobaric surface;
-
-    const mean_field::surface::ResolvedSurfaceCondition resolved = surface.resolve(equationOfState);
-
-    CHECK(surface.targetPressure() == 0.0);
-    CHECK(resolved.targetEnthalpy == 0.0);
-    CHECK(resolved.residual(0.0) == 0.0);
-    CHECK(resolved.residual(0.37) == 0.37);
-    CHECK(resolved.jacobianAction(-0.19) == -0.19);
-}
-
-TEST_CASE(
-    "Isobaric Surface Resolves Positive Pressure Through The EOS",
-    tags::barotrope &tags::unit &tags::surface
-) {
-    const mean_field::eos::Polytrope equationOfState(3.0, 0.25);
-
-    constexpr double targetPressure = 0.03125;
-
-    const mean_field::surface::Isobaric surface(targetPressure);
-
-    const mean_field::surface::ResolvedSurfaceCondition resolved = surface.resolve(equationOfState);
-
-    const double recoveredPressure = equationOfState.pressure_from_enthalpy(resolved.targetEnthalpy);
-
-    INFO("Resolved surface enthalpy = " << resolved.targetEnthalpy);
-    INFO("Recovered surface pressure = " << recoveredPressure);
-
-    CHECK(resolved.targetEnthalpy > 0.0);
-    CHECK(std::abs(recoveredPressure - targetPressure) < 64.0 * std::numeric_limits<double>::epsilon());
-    CHECK(resolved.residual(resolved.targetEnthalpy) == 0.0);
-}
-
-TEST_CASE(
-    "Isobaric Surface Rejects Invalid Pressure Targets",
-    tags::barotrope &tags::unit &tags::surface
-) {
-    CHECK_THROWS_AS(mean_field::surface::Isobaric(-1.0), std::invalid_argument);
-
-    CHECK_THROWS_AS(mean_field::surface::Isobaric(std::numeric_limits<double>::infinity()), std::invalid_argument);
-
-    CHECK_THROWS_AS(mean_field::surface::Isobaric(std::numeric_limits<double>::quiet_NaN()), std::invalid_argument);
-}
-
-TEST_CASE(
-    "Surface Base Dispatch Preserves The Isobaric Prescription",
-    tags::barotrope &tags::unit &tags::surface
-) {
-    const mean_field::eos::Polytrope equationOfState(3.0, 0.25);
-
-    const mean_field::surface::Isobaric isobaric(0.02);
-
-    const mean_field::surface::SurfaceBase &surface = isobaric;
-
-    surface.validate(equationOfState);
-
-    const mean_field::surface::ResolvedSurfaceCondition resolved = surface.resolve(equationOfState);
-
-    CHECK(resolved.targetEnthalpy > 0.0);
-    CHECK(resolved.residual(resolved.targetEnthalpy) == 0.0);
-}

tests/test_helpers.cppm

@@ -13,456 +13,469 @@ export module test_helpers;
 import mean_field;
 
 template <std::size_t N> struct Tag {
-  std::array<char, N> chars{};
+    std::array<char, N> chars{};
 
-  // ReSharper disable once CppNonExplicitConvertingConstructor
-  consteval Tag(std::array<char, N> arr) : chars(arr) {}
+    // ReSharper disable once CppNonExplicitConvertingConstructor
+    consteval Tag(
+        std::array<
+            char,
+            N> arr
+    )
+        : chars(arr) {
+    }
 
-  // ReSharper disable once CppNonExplicitConversionOperator
-  constexpr operator const char *() const { return chars.data(); }
+    // ReSharper disable once CppNonExplicitConversionOperator
+    constexpr operator const char *() const {
+        return chars.data();
+    }
 
-  // ReSharper disable once CppNonExplicitConversionOperator
-  constexpr operator Catch::StringRef() const {
-    return Catch::StringRef(chars.data(), N - 1);
-  }
+    // ReSharper disable once CppNonExplicitConversionOperator
+    constexpr operator Catch::StringRef() const {
+        return Catch::StringRef(chars.data(), N - 1);
+    }
 
-  template <std::size_t M>
-  consteval Tag<N + M - 1> operator&(const Tag<M> &other) const {
-    std::array<char, N + M - 1> res{};
-    std::ranges::copy(chars.begin(), chars.end() - 1, res.begin());
-    std::ranges::copy(other.chars, res.begin() + (N - 1));
-    return {res};
-  }
+    template <std::size_t M> consteval Tag<N + M - 1> operator&(const Tag<M> &other) const {
+        std::array<char, N + M - 1> res{};
+        std::ranges::copy(chars.begin(), chars.end() - 1, res.begin());
+        std::ranges::copy(other.chars, res.begin() + (N - 1));
+        return {res};
+    }
 };
 
 template <std::size_t N> consteval auto make_tag(const char (&str)[N]) {
-  std::array<char, N + 2> res{};
-  res[0] = '[';
-  std::ranges::copy(str, str + N - 1, res.begin() + 1);
-  res[N] = ']';
-  res[N + 1] = '\0';
-  return Tag<N + 2>{res};
+    std::array<char, N + 2> res{};
+    res[0] = '[';
+    std::ranges::copy(str, str + N - 1, res.begin() + 1);
+    res[N]     = ']';
+    res[N + 1] = '\0';
+    return Tag<N + 2>{res};
 }
 
-template <std::size_t N, std::size_t M>
-consteval auto sub_tag(const Tag<N> &parent, const char (&str)[M]) {
-  return parent & make_tag(str);
+template <
+    std::size_t N,
+    std::size_t M>
+consteval auto sub_tag(
+    const Tag<N> &parent,
+    const char (&str)[M]
+) {
+    return parent & make_tag(str);
 }
 
 namespace test_utils::detail {
-std::optional<mean_field::utils::Args> configured_args;
+    std::optional<mean_field::utils::Args> configured_args;
 
-mean_field::utils::Args make_default_args() {
-  mean_field::utils::Args args;
-  args.mesh_file = "sandbox.smesh";
-  args.p.rtol = 1.0e-12;
-  args.p.atol = 1.0e-12;
-  return args;
-}
+    mean_field::utils::Args make_default_args() {
+        mean_field::utils::Args args;
+        args.mesh_file = "sandbox.smesh";
+        args.p.rtol    = 1.0e-12;
+        args.p.atol    = 1.0e-12;
+        return args;
+    }
 } // namespace test_utils::detail
 
 export namespace test_utils {
-void set_args(mean_field::utils::Args args) {
-  detail::configured_args = std::move(args);
-}
+    void set_args(mean_field::utils::Args args) {
+        detail::configured_args = std::move(args);
+    }
 
-mean_field::utils::Args setup_args() {
-  if (detail::configured_args.has_value()) {
-    return *detail::configured_args;
-  }
+    mean_field::utils::Args setup_args() {
+        if (detail::configured_args.has_value()) {
+            return *detail::configured_args;
+        }
 
-  return detail::make_default_args();
-}
+        return detail::make_default_args();
+    }
 } // namespace test_utils
 
 export namespace gravity_prepared_test_utils {
-using DomainSchema = mean_field::utils::domain::CoreEnvelopeVacuumDomainSchema;
+    using DomainSchema = mean_field::utils::domain::CoreEnvelopeVacuumDomainSchema;
 
-template <typename FieldT>
-inline mean_field::field::FieldDofMap
-make_field_map(const mean_field::fem::FEM &f) {
-  if constexpr (std::same_as<FieldT, mean_field::field::Density>) {
-    return mean_field::field::make_field_dof_map<FieldT, DomainSchema>(
-        *f.densityFes);
-  } else if constexpr (std::same_as<FieldT, mean_field::field::Displacement>) {
-    return mean_field::field::make_field_dof_map<FieldT, DomainSchema>(
-        *f.displacementFes);
-  } else {
-    static_assert(std::same_as<FieldT, mean_field::field::Gravity>);
-    return mean_field::field::make_field_dof_map<FieldT, DomainSchema>(
-        *f.gravityFluxFes);
-  }
-}
-
-template <typename FieldT>
-inline mfem::Vector gather_field(const mean_field::fem::FEM &f,
-                                 const mfem::Vector &true_vector) {
-  return make_field_map<FieldT>(f).gather(true_vector);
-}
-
-inline mfem::Vector make_deterministic_vector(const int size,
-                                              const double phase = 0.0) {
-  mfem::Vector vector(size);
-
-  for (int i = 0; i < size; ++i) {
-    const double index = static_cast<double>(i + 1);
-    vector(i) = std::sin(0.37 * index + phase) +
-                0.31 * std::cos(0.19 * index - 0.5 * phase);
-  }
-
-  return vector;
-}
-
-inline mfem::Vector make_displacement(const mean_field::fem::FEM &f,
-                                      const double scale) {
-  mfem::ParGridFunction displacement(f.displacementFes.get());
-
-  auto displacement_function = [scale](const mfem::Vector &position,
-                                       mfem::Vector &value) {
-    value.SetSize(3);
-    value(0) = scale * (0.04 * position(0) + 0.01 * position(1) * position(2));
-    value(1) =
-        scale * (-0.03 * position(1) + 0.008 * position(0) * position(2));
-    value(2) = scale * (0.02 * position(2) - 0.006 * position(0) * position(1));
-  };
-
-  mfem::VectorFunctionCoefficient coefficient(f.mesh->Dimension(),
-                                              displacement_function);
-  displacement.ProjectCoefficient(coefficient);
-
-  mfem::Vector displacement_true;
-  displacement.GetTrueDofs(displacement_true);
-  return displacement_true;
-}
-
-inline mfem::Vector make_domain_supported_density(const mean_field::fem::FEM &f,
-                                                  const bool stellar) {
-  mfem::Vector attribute_values(f.mesh->attributes.Max());
-  attribute_values = 0.0;
-
-  using DomainSchema =
-      mean_field::utils::domain::CoreEnvelopeVacuumDomainSchema;
-
-  for (int i = 0; i < f.mesh->attributes.Size(); ++i) {
-    const int attribute = f.mesh->attributes[i];
-    const bool is_stellar = DomainSchema::template attribute_belongs_to<
-        mean_field::utils::domain::Stellar>(attribute);
-
-    if (is_stellar == stellar) {
-      attribute_values(attribute - 1) = 1.0;
+    template <typename FieldT> inline mean_field::field::FieldDofMap make_field_map(const mean_field::fem::FEM &f) {
+        if constexpr (std::same_as<FieldT, mean_field::field::Density>) {
+            return mean_field::field::make_field_dof_map<FieldT, DomainSchema>(*f.densityFes);
+        } else if constexpr (std::same_as<FieldT, mean_field::field::Displacement>) {
+            return mean_field::field::make_field_dof_map<FieldT, DomainSchema>(*f.displacementFes);
+        } else {
+            static_assert(std::same_as<FieldT, mean_field::field::Gravity>);
+            return mean_field::field::make_field_dof_map<FieldT, DomainSchema>(*f.gravityFluxFes);
+        }
     }
-  }
 
-  mfem::PWConstCoefficient coefficient(attribute_values);
-  mfem::ParGridFunction density(f.densityFes.get());
-  density.ProjectCoefficient(coefficient);
+    template <typename FieldT>
+    inline mfem::Vector gather_field(
+        const mean_field::fem::FEM &f,
+        const mfem::Vector &true_vector
+    ) {
+        return make_field_map<FieldT>(f).gather(true_vector);
+    }
 
-  mfem::Vector density_true;
-  density.GetTrueDofs(density_true);
-  return density_true;
-}
+    inline mfem::Vector make_deterministic_vector(
+        const int size,
+        const double phase = 0.0
+    ) {
+        mfem::Vector vector(size);
 
-inline mfem::Vector linear_combination(const mfem::Vector &first,
-                                       const double first_scale,
-                                       const mfem::Vector &second,
-                                       const double second_scale) {
-  MFEM_VERIFY(first.Size() == second.Size(),
-              "Cannot combine vectors with different sizes.");
+        for (int i = 0; i < size; ++i) {
+            const double index = static_cast<double>(i + 1);
+            vector(i)          = std::sin(0.37 * index + phase) + 0.31 * std::cos(0.19 * index - 0.5 * phase);
+        }
 
-  mfem::Vector combination(first);
-  combination *= first_scale;
-  combination.Add(second_scale, second);
-  return combination;
-}
+        return vector;
+    }
 
-inline double global_norm(const mfem::Vector &vector, MPI_Comm communicator) {
-  const double local_norm_squared = vector * vector;
-  double global_norm_squared = 0.0;
-  MPI_Allreduce(&local_norm_squared, &global_norm_squared, 1, MPI_DOUBLE,
-                MPI_SUM, communicator);
-  return std::sqrt(global_norm_squared);
-}
+    inline mfem::Vector make_displacement(
+        const mean_field::fem::FEM &f,
+        const double scale
+    ) {
+        mfem::ParGridFunction displacement(f.displacementFes.get());
 
-inline double global_dot(const mfem::Vector &first, const mfem::Vector &second,
-                         MPI_Comm communicator) {
-  MFEM_VERIFY(first.Size() == second.Size(),
-              "Cannot take the dot product of vectors with different sizes.");
+        auto displacement_function = [scale](const mfem::Vector &position, mfem::Vector &value) {
+            value.SetSize(3);
+            value(0) = scale * (0.04 * position(0) + 0.01 * position(1) * position(2));
+            value(1) = scale * (-0.03 * position(1) + 0.008 * position(0) * position(2));
+            value(2) = scale * (0.02 * position(2) - 0.006 * position(0) * position(1));
+        };
 
-  const double local_dot = first * second;
-  double global_dot = 0.0;
-  MPI_Allreduce(&local_dot, &global_dot, 1, MPI_DOUBLE, MPI_SUM, communicator);
-  return global_dot;
-}
+        mfem::VectorFunctionCoefficient coefficient(f.mesh->Dimension(), displacement_function);
+        displacement.ProjectCoefficient(coefficient);
 
-inline double relative_error(const mfem::Vector &computed,
-                             const mfem::Vector &reference,
-                             MPI_Comm communicator) {
-  MFEM_VERIFY(computed.Size() == reference.Size(),
-              "Cannot compare vectors with different sizes.");
+        mfem::Vector displacement_true;
+        displacement.GetTrueDofs(displacement_true);
+        return displacement_true;
+    }
 
-  mfem::Vector difference(computed);
-  difference -= reference;
+    inline mfem::Vector make_domain_supported_density(
+        const mean_field::fem::FEM &f,
+        const bool stellar
+    ) {
+        mfem::Vector attribute_values(f.mesh->attributes.Max());
+        attribute_values   = 0.0;
 
-  return global_norm(difference, communicator) /
-         std::max(global_norm(reference, communicator),
-                  std::numeric_limits<double>::epsilon());
-}
+        using DomainSchema = mean_field::utils::domain::CoreEnvelopeVacuumDomainSchema;
 
-inline double relative_scalar_error(const double computed,
-                                    const double reference) {
-  return std::abs(computed - reference) /
-         std::max(std::abs(reference), std::numeric_limits<double>::epsilon());
-}
+        for (int i = 0; i < f.mesh->attributes.Size(); ++i) {
+            const int attribute = f.mesh->attributes[i];
+            const bool is_stellar =
+                DomainSchema::template attribute_belongs_to<mean_field::utils::domain::Stellar>(attribute);
+
+            if (is_stellar == stellar) {
+                attribute_values(attribute - 1) = 1.0;
+            }
+        }
+
+        mfem::PWConstCoefficient coefficient(attribute_values);
+        mfem::ParGridFunction density(f.densityFes.get());
+        density.ProjectCoefficient(coefficient);
+
+        mfem::Vector density_true;
+        density.GetTrueDofs(density_true);
+        return density_true;
+    }
+
+    inline mfem::Vector linear_combination(
+        const mfem::Vector &first,
+        const double first_scale,
+        const mfem::Vector &second,
+        const double second_scale
+    ) {
+        MFEM_VERIFY(first.Size() == second.Size(), "Cannot combine vectors with different sizes.");
+
+        mfem::Vector combination(first);
+        combination *= first_scale;
+        combination.Add(second_scale, second);
+        return combination;
+    }
+
+    inline double global_norm(
+        const mfem::Vector &vector,
+        MPI_Comm communicator
+    ) {
+        const double local_norm_squared = vector * vector;
+        double global_norm_squared      = 0.0;
+        MPI_Allreduce(&local_norm_squared, &global_norm_squared, 1, MPI_DOUBLE, MPI_SUM, communicator);
+        return std::sqrt(global_norm_squared);
+    }
+
+    inline double global_dot(
+        const mfem::Vector &first,
+        const mfem::Vector &second,
+        MPI_Comm communicator
+    ) {
+        MFEM_VERIFY(first.Size() == second.Size(), "Cannot take the dot product of vectors with different sizes.");
+
+        const double local_dot = first * second;
+        double global_dot      = 0.0;
+        MPI_Allreduce(&local_dot, &global_dot, 1, MPI_DOUBLE, MPI_SUM, communicator);
+        return global_dot;
+    }
+
+    inline double relative_error(
+        const mfem::Vector &computed,
+        const mfem::Vector &reference,
+        MPI_Comm communicator
+    ) {
+        MFEM_VERIFY(computed.Size() == reference.Size(), "Cannot compare vectors with different sizes.");
+
+        mfem::Vector difference(computed);
+        difference -= reference;
+
+        return global_norm(difference, communicator) /
+               std::max(global_norm(reference, communicator), std::numeric_limits<double>::epsilon());
+    }
+
+    inline double relative_scalar_error(
+        const double computed,
+        const double reference
+    ) {
+        return std::abs(computed - reference) / std::max(std::abs(reference), std::numeric_limits<double>::epsilon());
+    }
 } // namespace gravity_prepared_test_utils
 
 export namespace field_dof_test_utils {
-using DomainSchema = mean_field::utils::domain::CoreEnvelopeVacuumDomainSchema;
+    using DomainSchema = mean_field::utils::domain::CoreEnvelopeVacuumDomainSchema;
 
-inline mean_field::mapping::DomainMapper make_domain_mapper() {
-  const mean_field::utils::Args args = test_utils::setup_args();
-  return mean_field::mapping::DomainMapper(
-      args.domain_mapper_options,
-      std::make_unique<const mean_field::mapping::compactification::
-                           KelvinCompactification>(args.kelvin_options));
-}
+    inline mean_field::mapping::DomainMapper make_domain_mapper() {
+        const mean_field::utils::Args args = test_utils::setup_args();
+        return mean_field::mapping::DomainMapper(
+            args.domain_mapper_options,
+            std::make_unique<const mean_field::mapping::compactification::KelvinCompactification>(args.kelvin_options)
+        );
+    }
 
-inline constexpr int vacuum_material_attribute =
-    DomainSchema::template material_attribute<
-        mean_field::utils::domain::Vacuum>();
+    inline constexpr int vacuum_material_attribute =
+        DomainSchema::template material_attribute<mean_field::utils::domain::Vacuum>();
 
-template <typename FieldT>
-inline mean_field::field::FieldDofMap
-make_map(const mfem::ParFiniteElementSpace &finiteElementSpace) {
-  return mean_field::field::make_field_dof_map<FieldT, DomainSchema>(
-      finiteElementSpace);
-}
+    template <typename FieldT>
+    inline mean_field::field::FieldDofMap make_map(const mfem::ParFiniteElementSpace &finiteElementSpace) {
+        return mean_field::field::make_field_dof_map<FieldT, DomainSchema>(finiteElementSpace);
+    }
 
-template <typename FieldT>
-inline mfem::Vector make_deterministic_supported_vector(
-    const mfem::ParFiniteElementSpace &finiteElementSpace, const double phase) {
-  const mean_field::field::FieldDofMap map =
-      make_map<FieldT>(finiteElementSpace);
-  const mfem::Vector full =
-      gravity_prepared_test_utils::make_deterministic_vector(map.full_size(),
-                                                             phase);
-  return map.gather(full);
-}
+    template <typename FieldT>
+    inline mfem::Vector make_deterministic_supported_vector(
+        const mfem::ParFiniteElementSpace &finiteElementSpace,
+        const double phase
+    ) {
+        const mean_field::field::FieldDofMap map = make_map<FieldT>(finiteElementSpace);
+        const mfem::Vector full = gravity_prepared_test_utils::make_deterministic_vector(map.full_size(), phase);
+        return map.gather(full);
+    }
 
-inline mfem::Vector make_supported_displacement(const mean_field::fem::FEM &f,
-                                                const double phase) {
-  const mean_field::field::FieldDofMap map =
-      make_map<mean_field::field::Displacement>(*f.displacementFes);
-  return map.gather(gravity_prepared_test_utils::make_displacement(f, phase));
-}
+    inline mfem::Vector make_supported_displacement(
+        const mean_field::fem::FEM &f,
+        const double phase
+    ) {
+        const mean_field::field::FieldDofMap map = make_map<mean_field::field::Displacement>(*f.displacementFes);
+        return map.gather(gravity_prepared_test_utils::make_displacement(f, phase));
+    }
 
-inline void apply_hydrostatic_reference(
-    const mean_field::fem::FEM &f,
-    const mean_field::physics::RigidRotation &rotation,
-    const mfem::Vector &enthalpy, const mfem::Vector &gravityPotential,
-    const mfem::Vector &displacement, const double bernoulliConstant,
-    mfem::Vector &residual) {
-  const mean_field::field::FieldDofMap enthalpyMap =
-      make_map<mean_field::field::Enthalpy>(*f.enthalpyFes);
-  const mean_field::field::FieldDofMap gravityPotentialMap =
-      make_map<mean_field::field::Gravity>(*f.gravityPotentialFes);
-  const mean_field::field::FieldDofMap displacementMap =
-      make_map<mean_field::field::Displacement>(*f.displacementFes);
+    inline void apply_hydrostatic_reference(
+        const mean_field::fem::FEM &f,
+        const mean_field::physics::RigidRotation &rotation,
+        const mfem::Vector &enthalpy,
+        const mfem::Vector &gravityPotential,
+        const mfem::Vector &displacement,
+        const double bernoulliConstant,
+        mfem::Vector &residual
+    ) {
+        const mean_field::field::FieldDofMap enthalpyMap = make_map<mean_field::field::Enthalpy>(*f.enthalpyFes);
+        const mean_field::field::FieldDofMap gravityPotentialMap =
+            make_map<mean_field::field::Gravity>(*f.gravityPotentialFes);
+        const mean_field::field::FieldDofMap displacementMap =
+            make_map<mean_field::field::Displacement>(*f.displacementFes);
 
-  mfem::Vector enthalpyTrue(enthalpyMap.full_size());
-  mfem::Vector gravityPotentialTrue(gravityPotentialMap.full_size());
-  mfem::Vector displacementTrue(displacementMap.full_size());
-  mfem::Vector residualTrue;
+        mfem::Vector enthalpyTrue(enthalpyMap.full_size());
+        mfem::Vector gravityPotentialTrue(gravityPotentialMap.full_size());
+        mfem::Vector displacementTrue(displacementMap.full_size());
+        mfem::Vector residualTrue;
 
-  enthalpyMap.scatter(enthalpy, enthalpyTrue);
-  gravityPotentialMap.scatter(gravityPotential, gravityPotentialTrue);
-  displacementMap.scatter(displacement, displacementTrue);
+        enthalpyMap.scatter(enthalpy, enthalpyTrue);
+        gravityPotentialMap.scatter(gravityPotential, gravityPotentialTrue);
+        displacementMap.scatter(displacement, displacementTrue);
 
-  mean_field::operators::kernels::apply_hydrostatic_equilibrium(
-      f, *f.domainMapperStateless, rotation, enthalpyTrue, gravityPotentialTrue,
-      displacementTrue, bernoulliConstant, residualTrue);
+        mean_field::operators::kernels::apply_hydrostatic_equilibrium(
+            f, *f.domainMapperStateless, rotation, enthalpyTrue, gravityPotentialTrue, displacementTrue,
+            bernoulliConstant, residualTrue
+        );
 
-  residual.SetSize(enthalpyMap.reduced_size());
-  enthalpyMap.gather(residualTrue, residual);
-}
+        residual.SetSize(enthalpyMap.reduced_size());
+        enthalpyMap.gather(residualTrue, residual);
+    }
 } // namespace field_dof_test_utils
 
 export namespace tags {
-inline constexpr auto geometry = make_tag("geometry");
-inline constexpr auto physics = make_tag("physics");
-inline constexpr auto unit = make_tag("unit");
-inline constexpr auto mesh = make_tag("mesh");
-inline constexpr auto integration = make_tag("integration");
-inline constexpr auto solver = make_tag("solver");
-inline constexpr auto integrator = make_tag("integrator");
-inline constexpr auto mapping = make_tag("mapping");
-inline constexpr auto utils = make_tag("utils");
-inline constexpr auto mfem_operators = make_tag("operators");
-inline constexpr auto initialization = make_tag("initialization");
-inline constexpr auto accuracy = make_tag("accuracy");
-inline constexpr auto closure = make_tag("closure");
-inline constexpr auto kernels = make_tag("kernels");
-inline constexpr auto surface = make_tag("surface");
-inline constexpr auto model = make_tag("model");
+    inline constexpr auto geometry                     = make_tag("geometry");
+    inline constexpr auto physics                      = make_tag("physics");
+    inline constexpr auto unit                         = make_tag("unit");
+    inline constexpr auto mesh                         = make_tag("mesh");
+    inline constexpr auto integration                  = make_tag("integration");
+    inline constexpr auto solver                       = make_tag("solver");
+    inline constexpr auto integrator                   = make_tag("integrator");
+    inline constexpr auto mapping                      = make_tag("mapping");
+    inline constexpr auto utils                        = make_tag("utils");
+    inline constexpr auto mfem_operators               = make_tag("operators");
+    inline constexpr auto initialization               = make_tag("initialization");
+    inline constexpr auto accuracy                     = make_tag("accuracy");
+    inline constexpr auto closure                      = make_tag("closure");
+    inline constexpr auto kernels                      = make_tag("kernels");
+    inline constexpr auto surface                      = make_tag("surface");
+    inline constexpr auto model                        = make_tag("model");
 
-inline constexpr auto field = sub_tag(mesh & physics, "field");
-inline constexpr auto field_dof = field & make_tag("dof");
-inline constexpr auto field_dof_unit = field_dof & unit;
-inline constexpr auto field_dof_integration = field_dof & integration;
+    inline constexpr auto field                        = sub_tag(mesh & physics, "field");
+    inline constexpr auto field_dof                    = field & make_tag("dof");
+    inline constexpr auto field_dof_unit               = field_dof & unit;
+    inline constexpr auto field_dof_integration        = field_dof & integration;
 
-inline constexpr auto pressure = sub_tag(physics, "pressure");
+    inline constexpr auto pressure                     = sub_tag(physics, "pressure");
 
-inline constexpr auto hydro = sub_tag(physics, "hydro");
-inline constexpr auto jacobian = sub_tag(integration & physics, "jacobian");
-inline constexpr auto residuals = sub_tag(integration & physics, "residuals");
-inline constexpr auto volume = sub_tag(mesh & geometry, "volume");
-inline constexpr auto quadrature =
-    sub_tag(mesh & geometry & solver, "quadrature");
-inline constexpr auto convergence = sub_tag(solver, "convergence");
-inline constexpr auto transformations =
-    sub_tag(mesh & geometry, "transformations");
+    inline constexpr auto hydro                        = sub_tag(physics, "hydro");
+    inline constexpr auto jacobian                     = sub_tag(integration & physics, "jacobian");
+    inline constexpr auto residuals                    = sub_tag(integration & physics, "residuals");
+    inline constexpr auto volume                       = sub_tag(mesh & geometry, "volume");
+    inline constexpr auto quadrature                   = sub_tag(mesh & geometry & solver, "quadrature");
+    inline constexpr auto convergence                  = sub_tag(solver, "convergence");
+    inline constexpr auto transformations              = sub_tag(mesh & geometry, "transformations");
 
-inline constexpr auto h_refinement =
-    sub_tag(mesh & convergence, "h_refinement");
-inline constexpr auto p_refinement =
-    sub_tag(mesh & convergence, "p_refinement");
+    inline constexpr auto h_refinement                 = sub_tag(mesh & convergence, "h_refinement");
+    inline constexpr auto p_refinement                 = sub_tag(mesh & convergence, "p_refinement");
 
-inline constexpr auto analytic_comparison =
-    sub_tag(solver & physics & residuals, "analytic_comparison");
-inline constexpr auto self_consistency =
-    sub_tag(solver & physics, "self_consistency");
+    inline constexpr auto analytic_comparison          = sub_tag(solver & physics & residuals, "analytic_comparison");
+    inline constexpr auto self_consistency             = sub_tag(solver & physics, "self_consistency");
 
-inline constexpr auto centrifugal = sub_tag(solver & physics, "centrifugal");
-inline constexpr auto advection = sub_tag(solver & physics, "advection");
-inline constexpr auto coriolis = sub_tag(solver & physics, "coriolis");
-inline constexpr auto gravity = sub_tag(solver & physics, "gravity");
-inline constexpr auto enthalpy = sub_tag(solver & physics, "enthalpy");
-inline constexpr auto barotrope = sub_tag(physics, "barotrope");
-inline constexpr auto mass_continuity =
-    sub_tag(solver & physics, "mass_continuity");
-inline constexpr auto pressure_gradient =
-    sub_tag(solver & physics, "pressure_gradient");
-inline constexpr auto viscosity = sub_tag(solver & physics, "viscosity");
+    inline constexpr auto centrifugal                  = sub_tag(solver & physics, "centrifugal");
+    inline constexpr auto advection                    = sub_tag(solver & physics, "advection");
+    inline constexpr auto coriolis                     = sub_tag(solver & physics, "coriolis");
+    inline constexpr auto gravity                      = sub_tag(solver & physics, "gravity");
+    inline constexpr auto enthalpy                     = sub_tag(solver & physics, "enthalpy");
+    inline constexpr auto barotrope                    = sub_tag(physics, "barotrope");
+    inline constexpr auto mass_continuity              = sub_tag(solver & physics, "mass_continuity");
+    inline constexpr auto pressure_gradient            = sub_tag(solver & physics, "pressure_gradient");
+    inline constexpr auto viscosity                    = sub_tag(solver & physics, "viscosity");
 
-inline constexpr auto compactification =
-    sub_tag(mesh & mapping, "compactification");
-inline constexpr auto kelvin = sub_tag(compactification, "kelvin");
-inline constexpr auto mapping_evaluator =
-    mapping & make_tag("grid_function_evaluator");
-inline constexpr auto mapping_evaluator_unit = mapping_evaluator & unit;
+    inline constexpr auto compactification             = sub_tag(mesh & mapping, "compactification");
+    inline constexpr auto kelvin                       = sub_tag(compactification, "kelvin");
+    inline constexpr auto mapping_evaluator            = mapping & make_tag("grid_function_evaluator");
+    inline constexpr auto mapping_evaluator_unit       = mapping_evaluator & unit;
 
-inline constexpr auto prepared = sub_tag(solver & physics, "prepared");
-inline constexpr auto contexts = sub_tag(solver, "contexts");
+    inline constexpr auto prepared                     = sub_tag(solver & physics, "prepared");
+    inline constexpr auto contexts                     = sub_tag(solver, "contexts");
 
-inline constexpr auto domain = sub_tag(mesh, "domain");
+    inline constexpr auto domain                       = sub_tag(mesh, "domain");
 
-// Canonical gravity-suite tags. These intentionally compose leaf tags
-// exactly once so Catch2 output remains useful and free of repeated
-// [solver]/[physics] entries inherited from older composite tags.
-inline constexpr auto gravity_unit = gravity & unit;
-inline constexpr auto gravity_integration = gravity & integration;
-inline constexpr auto gravity_operator = gravity & mfem_operators;
-inline constexpr auto gravity_prepared = gravity & make_tag("prepared");
-inline constexpr auto gravity_context = gravity & make_tag("context");
-inline constexpr auto gravity_kernel = gravity & kernels;
-inline constexpr auto gravity_accuracy = gravity & accuracy;
-inline constexpr auto gravity_operator_unit = gravity_operator & unit;
-inline constexpr auto gravity_operator_integration =
-    gravity_operator & integration;
-inline constexpr auto gravity_operator_convergence =
-    gravity_operator & integration & make_tag("convergence");
-inline constexpr auto gravity_analytic =
-    gravity & integration & make_tag("analytic_comparison");
-inline constexpr auto gravity_consistency =
-    gravity & integration & make_tag("self_consistency");
-inline constexpr auto gravity_prepared_jacobian =
-    gravity_prepared & integration & make_tag("jacobian");
-inline constexpr auto gravity_prepared_unit = gravity_prepared & unit;
-inline constexpr auto gravity_prepared_jacobian_accuracy =
-    gravity_prepared_jacobian & accuracy;
-inline constexpr auto gravity_kernel_accuracy = gravity_kernel & accuracy;
-inline constexpr auto gravity_kernel_integration = gravity_kernel & integration;
-inline constexpr auto gravity_kernel_convergence =
-    gravity_kernel & integration & make_tag("convergence");
-inline constexpr auto gravity_analytic_accuracy = gravity_analytic & accuracy;
-inline constexpr auto gravity_consistency_accuracy =
-    gravity_consistency & accuracy;
-inline constexpr auto gravity_integrator_unit = gravity & integrator & unit;
+    // Canonical gravity-suite tags. These intentionally compose leaf tags
+    // exactly once so Catch2 output remains useful and free of repeated
+    // [solver]/[physics] entries inherited from older composite tags.
+    inline constexpr auto gravity_unit                 = gravity & unit;
+    inline constexpr auto gravity_integration          = gravity & integration;
+    inline constexpr auto gravity_operator             = gravity & mfem_operators;
+    inline constexpr auto gravity_prepared             = gravity & make_tag("prepared");
+    inline constexpr auto gravity_context              = gravity & make_tag("context");
+    inline constexpr auto gravity_kernel               = gravity & kernels;
+    inline constexpr auto gravity_accuracy             = gravity & accuracy;
+    inline constexpr auto gravity_operator_unit        = gravity_operator & unit;
+    inline constexpr auto gravity_operator_integration = gravity_operator & integration;
+    inline constexpr auto gravity_operator_convergence = gravity_operator & integration & make_tag("convergence");
+    inline constexpr auto gravity_analytic             = gravity & integration & make_tag("analytic_comparison");
+    inline constexpr auto gravity_consistency          = gravity & integration & make_tag("self_consistency");
+    inline constexpr auto gravity_prepared_jacobian    = gravity_prepared & integration & make_tag("jacobian");
+    inline constexpr auto gravity_prepared_unit        = gravity_prepared & unit;
+    inline constexpr auto gravity_prepared_jacobian_accuracy = gravity_prepared_jacobian & accuracy;
+    inline constexpr auto gravity_kernel_accuracy            = gravity_kernel & accuracy;
+    inline constexpr auto gravity_kernel_integration         = gravity_kernel & integration;
+    inline constexpr auto gravity_kernel_convergence         = gravity_kernel & integration & make_tag("convergence");
+    inline constexpr auto gravity_analytic_accuracy          = gravity_analytic & accuracy;
+    inline constexpr auto gravity_consistency_accuracy       = gravity_consistency & accuracy;
+    inline constexpr auto gravity_integrator_unit            = gravity & integrator & unit;
 
-inline constexpr auto barotrope_prepared =
-    barotrope & solver & make_tag("prepared");
-inline constexpr auto barotrope_eos_unit = barotrope & unit & make_tag("eos");
-inline constexpr auto barotrope_eos_jacobian =
-    barotrope_eos_unit & integration & make_tag("jacobian");
-inline constexpr auto barotrope_pressure_quadrature =
-    barotrope & mesh & geometry & solver & make_tag("pressure") &
-    make_tag("pressure_gradient") & make_tag("quadrature");
-inline constexpr auto barotrope_pressure_quadrature_unit =
-    barotrope_pressure_quadrature & unit;
-inline constexpr auto barotrope_pressure_quadrature_accuracy =
-    barotrope_pressure_quadrature & accuracy;
-inline constexpr auto barotrope_prepared_jacobian =
-    barotrope_prepared & integration & make_tag("jacobian");
-inline constexpr auto barotrope_context =
-    barotrope & solver & make_tag("context");
-inline constexpr auto barotrope_context_integration =
-    barotrope_context & integration;
-inline constexpr auto barotrope_prepared_analytic =
-    barotrope_prepared & integration & make_tag("analytic_comparison");
-inline constexpr auto barotrope_prepared_jacobian_accuracy =
-    barotrope_prepared_jacobian & accuracy;
-inline constexpr auto barotrope_prepared_jacobian_geometry =
-    barotrope_prepared_jacobian & geometry;
-inline constexpr auto barotrope_prepared_jacobian_unit =
-    barotrope_prepared_jacobian & unit;
+    inline constexpr auto barotrope_prepared                 = barotrope & solver & make_tag("prepared");
+    inline constexpr auto barotrope_eos_unit                 = barotrope & unit & make_tag("eos");
+    inline constexpr auto barotrope_eos_jacobian             = barotrope_eos_unit & integration & make_tag("jacobian");
+    inline constexpr auto polytropic_eos_characterization =
+        barotrope & unit & make_tag("eos") & make_tag("characterization");
+    inline constexpr auto polytropic_eos_relation_contract =
+        barotrope & unit & make_tag("eos") & make_tag("relation_contract");
+    inline constexpr auto polytropic_eos_compatibility = barotrope & unit & make_tag("eos") & make_tag("compatibility");
+    inline constexpr auto equation_of_state            = physics & make_tag("eos");
+    inline constexpr auto equation_of_state_type_system    = equation_of_state & unit & make_tag("type_system");
+    inline constexpr auto equation_of_state_quantity_types = equation_of_state_type_system & make_tag("quantity_types");
+    inline constexpr auto equation_of_state_relation_contract =
+        equation_of_state_type_system & make_tag("relation_contract");
+    inline constexpr auto equation_of_state_runtime_view = equation_of_state & unit & make_tag("runtime_view");
+    inline constexpr auto equation_of_state_runtime_contract =
+        equation_of_state_runtime_view & make_tag("relation_contract");
+    inline constexpr auto equation_of_state_runtime_compatibility =
+        equation_of_state_runtime_view & make_tag("compatibility");
+    inline constexpr auto equation_of_state_consumer_contract =
+        equation_of_state & unit & make_tag("consumer_contract");
+    inline constexpr auto barotropic_closure_equation_of_state_contract =
+        equation_of_state_consumer_contract & make_tag("barotropic_closure");
+    inline constexpr auto pressure_force_equation_of_state_contract =
+        equation_of_state_consumer_contract & make_tag("pressure_force");
+    inline constexpr auto structure_seed_equation_of_state_contract =
+        equation_of_state_consumer_contract & make_tag("structure_seed");
+    inline constexpr auto stellar_model_type_contract = barotrope & model & unit & make_tag("type_contract");
+    inline constexpr auto stellar_model_runtime_view  = barotrope & model & unit & make_tag("runtime_view");
+    inline constexpr auto surface_prescription_type_contract =
+        surface & physics & unit & make_tag("prescription") & make_tag("type_contract");
+    inline constexpr auto surface_constraint_compilation =
+        surface & physics & unit & make_tag("constraint_compilation");
+    inline constexpr auto surface_constraint_jacobian = surface_constraint_compilation & jacobian;
+    inline constexpr auto surface_constraint_lifetime = surface & model & unit & make_tag("constraint_lifetime");
+    inline constexpr auto surface_boundary_dof_topology =
+        surface & field_dof & integration & make_tag("boundary_topology");
+    inline constexpr auto surface_row_replacement =
+        surface & barotrope_prepared & integration & make_tag("row_replacement");
+    inline constexpr auto translational_centering = geometry & solver & make_tag("translational_centering");
+    inline constexpr auto translational_centering_topology =
+        translational_centering & field_dof & integration & make_tag("point_topology");
+    inline constexpr auto translational_centering_enforcement =
+        translational_centering & barotrope_prepared & integration & make_tag("row_replacement");
+    inline constexpr auto barotrope_pressure_quadrature = barotrope & mesh & geometry & solver & make_tag("pressure") &
+                                                          make_tag("pressure_gradient") & make_tag("quadrature");
+    inline constexpr auto barotrope_pressure_quadrature_unit     = barotrope_pressure_quadrature & unit;
+    inline constexpr auto barotrope_pressure_quadrature_accuracy = barotrope_pressure_quadrature & accuracy;
+    inline constexpr auto barotrope_prepared_jacobian   = barotrope_prepared & integration & make_tag("jacobian");
+    inline constexpr auto barotrope_context             = barotrope & solver & make_tag("context");
+    inline constexpr auto barotrope_context_integration = barotrope_context & integration;
+    inline constexpr auto barotrope_prepared_analytic =
+        barotrope_prepared & integration & make_tag("analytic_comparison");
+    inline constexpr auto barotrope_prepared_jacobian_accuracy = barotrope_prepared_jacobian & accuracy;
+    inline constexpr auto barotrope_prepared_jacobian_geometry = barotrope_prepared_jacobian & geometry;
+    inline constexpr auto barotrope_prepared_jacobian_unit     = barotrope_prepared_jacobian & unit;
 
-// Canonical hydrostatic-suite tags. The leaf tags are composed directly
-// so inherited [physics]/[solver] tags appear only once.
-inline constexpr auto barotrope_hydrostatic =
-    barotrope & solver & make_tag("hydro");
-inline constexpr auto barotrope_hydrostatic_context =
-    barotrope_hydrostatic & make_tag("context");
-inline constexpr auto barotrope_hydrostatic_prepared =
-    barotrope_hydrostatic & make_tag("prepared");
-inline constexpr auto barotrope_hydrostatic_prepared_residual =
-    barotrope_hydrostatic_prepared & integration & make_tag("residual");
-inline constexpr auto barotrope_hydrostatic_prepared_jacobian =
-    barotrope_hydrostatic_prepared & integration & make_tag("jacobian");
-inline constexpr auto barotrope_hydrostatic_prepared_analytic =
-    barotrope_hydrostatic_prepared & integration &
-    make_tag("analytic_comparison");
+    // Canonical hydrostatic-suite tags. The leaf tags are composed directly
+    // so inherited [physics]/[solver] tags appear only once.
+    inline constexpr auto barotrope_hydrostatic                = barotrope & solver & make_tag("hydro");
+    inline constexpr auto barotrope_hydrostatic_context        = barotrope_hydrostatic & make_tag("context");
+    inline constexpr auto barotrope_hydrostatic_prepared       = barotrope_hydrostatic & make_tag("prepared");
+    inline constexpr auto barotrope_hydrostatic_prepared_residual =
+        barotrope_hydrostatic_prepared & integration & make_tag("residual");
+    inline constexpr auto barotrope_hydrostatic_prepared_jacobian =
+        barotrope_hydrostatic_prepared & integration & make_tag("jacobian");
+    inline constexpr auto barotrope_hydrostatic_prepared_analytic =
+        barotrope_hydrostatic_prepared & integration & make_tag("analytic_comparison");
 
-inline constexpr auto barotrope_mass_normalization =
-    barotrope & solver & make_tag("mass_normalization");
-inline constexpr auto barotrope_mass_normalization_context =
-    barotrope_mass_normalization & make_tag("context");
-inline constexpr auto barotrope_mass_normalization_prepared =
-    barotrope_mass_normalization & make_tag("prepared");
-inline constexpr auto barotrope_mass_normalization_jacobian =
-    barotrope_mass_normalization_prepared & integration & make_tag("jacobian");
-inline constexpr auto barotrope_mass_normalization_analytic =
-    barotrope_mass_normalization_prepared & integration &
-    make_tag("analytic_comparison");
+    inline constexpr auto barotrope_mass_normalization          = barotrope & solver & make_tag("mass_normalization");
+    inline constexpr auto barotrope_mass_normalization_context  = barotrope_mass_normalization & make_tag("context");
+    inline constexpr auto barotrope_mass_normalization_prepared = barotrope_mass_normalization & make_tag("prepared");
+    inline constexpr auto barotrope_mass_normalization_jacobian =
+        barotrope_mass_normalization_prepared & integration & make_tag("jacobian");
+    inline constexpr auto barotrope_mass_normalization_analytic =
+        barotrope_mass_normalization_prepared & integration & make_tag("analytic_comparison");
 
-inline constexpr auto rotation_prepared = centrifugal & make_tag("prepared");
-inline constexpr auto rotation_context = centrifugal & make_tag("context");
-inline constexpr auto rotation_analytic =
-    centrifugal & integration & make_tag("analytic_comparison");
-inline constexpr auto rotation_context_unit = rotation_context & unit;
-inline constexpr auto rotation_prepared_unit = rotation_prepared & unit;
-inline constexpr auto rotation_prepared_jacobian =
-    rotation_prepared & integration & make_tag("jacobian");
-inline constexpr auto rotation_prepared_jacobian_accuracy =
-    rotation_prepared_jacobian & accuracy;
-inline constexpr auto rotation_kernel_accuracy =
-    centrifugal & kernels & accuracy;
-inline constexpr auto rotation_integrator_unit = centrifugal & integrator & unit;
-inline constexpr auto rotation_integrator_integration =
-    centrifugal & integrator & integration;
-inline constexpr auto rotation_integrator_convergence =
-    rotation_integrator_integration & convergence & h_refinement;
-inline constexpr auto rotation_analytic_unit = rotation_analytic & unit;
-inline constexpr auto rotation_analytic_accuracy = rotation_analytic & accuracy;
-inline constexpr auto rotation_analytic_accuracy_geometry =
-    rotation_analytic_accuracy & geometry;
+    inline constexpr auto rotation_prepared          = centrifugal & make_tag("prepared");
+    inline constexpr auto rotation_context           = centrifugal & make_tag("context");
+    inline constexpr auto rotation_analytic          = centrifugal & integration & make_tag("analytic_comparison");
+    inline constexpr auto rotation_context_unit      = rotation_context & unit;
+    inline constexpr auto rotation_prepared_unit     = rotation_prepared & unit;
+    inline constexpr auto rotation_prepared_jacobian = rotation_prepared & integration & make_tag("jacobian");
+    inline constexpr auto rotation_prepared_jacobian_accuracy = rotation_prepared_jacobian & accuracy;
+    inline constexpr auto rotation_kernel_accuracy            = centrifugal & kernels & accuracy;
+    inline constexpr auto rotation_integrator_unit            = centrifugal & integrator & unit;
+    inline constexpr auto rotation_integrator_integration     = centrifugal & integrator & integration;
+    inline constexpr auto rotation_integrator_convergence =
+        rotation_integrator_integration & convergence & h_refinement;
+    inline constexpr auto rotation_analytic_unit              = rotation_analytic & unit;
+    inline constexpr auto rotation_analytic_accuracy          = rotation_analytic & accuracy;
+    inline constexpr auto rotation_analytic_accuracy_geometry = rotation_analytic_accuracy & geometry;
 
 } // namespace tags

tests/test_main.cpp

@@ -3,6 +3,7 @@
 #include <catch2/catch_test_case_info.hpp>
 #include <catch2/reporters/catch_reporter_registrars.hpp>
 #include <catch2/reporters/catch_reporter_streaming_base.hpp>
+#include <chrono>
 #include <fstream>
 #include <iomanip>
 #include <iostream>
@@ -223,6 +224,7 @@ class CheckReporter : public Catch::StreamingReporterBase {
         bool passed;
         std::size_t assertionsPassed;
         std::size_t assertionsFailed;
+        double durationSeconds;
         std::vector<std::string> failureMessages;
         std::vector<std::string> infoMessages;
     };
@@ -231,6 +233,7 @@ class CheckReporter : public Catch::StreamingReporterBase {
     std::vector<std::string> m_currentInfos;
     std::unordered_set<unsigned int> m_currentInfoSequences;
     std::vector<TestCaseData> m_testRunData;
+    std::chrono::time_point<std::chrono::steady_clock> m_testStartTime;
 
     void captureInfoMessages(Catch::AssertionStats const &assertionStats) {
         for (auto const &message : assertionStats.infoMessages) {
@@ -253,9 +256,8 @@ public:
     }
 
     static std::string getDescription() {
-        return "Console reporter with wrapping, tags, and collapsible HTML "
-               "export "
-               "with ANSI color rendering.";
+        return "Console reporter with wrapping, tags, live test progress, and collapsible HTML "
+               "export with ANSI color rendering.";
     }
 
     void testRunStarting(Catch::TestRunInfo const &_testRunInfo) override {
@@ -263,8 +265,20 @@ public:
 
         std::cout << '\n';
         std::cout << std::left << std::setw(85) << "Test Case Name"
-                  << "Status    " << std::right << std::setw(8) << "Passed" << std::setw(8) << "Failed" << '\n';
-        std::cout << std::string(121, '-') << '\n';
+                  << "Status    " << std::right << std::setw(8) << "Passed" << std::setw(8) << "Failed" << std::setw(12)
+                  << "Time (s)" << '\n';
+        std::cout << std::string(133, '-') << '\n';
+    }
+
+    void testCaseStarting(Catch::TestCaseInfo const &testInfo) override {
+        StreamingReporterBase::testCaseStarting(testInfo);
+
+        m_testStartTime  = std::chrono::steady_clock::now();
+        std::string name = testInfo.name;
+        auto wrappedName = wrapText(name, 83);
+
+        // Print progress line, \r to overwrite later, \033[K to clear till end of line
+        std::cout << "\r\033[K" << std::left << std::setw(85) << (wrappedName[0] + " ...") << std::flush;
     }
 
     void assertionEnded(Catch::AssertionStats const &assertionStats) override {
@@ -300,14 +314,20 @@ public:
     void testCaseEnded(Catch::TestCaseStats const &stats) override {
         StreamingReporterBase::testCaseEnded(stats);
 
-        bool passed      = stats.totals.assertions.allPassed();
-        std::string mark = passed ? "\033[32m✓\033[0m" : "\033[31m✗\033[0m";
+        auto endTime                          = std::chrono::steady_clock::now();
+        std::chrono::duration<double> elapsed = endTime - m_testStartTime;
+        double duration_s                     = elapsed.count();
 
-        std::string name = stats.testInfo->name;
-        auto wrappedName = wrapText(name, 83);
+        bool passed                           = stats.totals.assertions.allPassed();
+        std::string mark                      = passed ? "\033[32m✓\033[0m" : "\033[31m✗\033[0m";
 
-        std::cout << std::left << std::setw(85) << wrappedName[0] << mark << "         " << std::right << std::setw(8)
-                  << stats.totals.assertions.passed << std::setw(8) << stats.totals.assertions.failed << '\n';
+        std::string name                      = stats.testInfo->name;
+        auto wrappedName                      = wrapText(name, 83);
+
+        // Overwrite the loading line with the actual result
+        std::cout << "\r\033[K" << std::left << std::setw(85) << wrappedName[0] << mark << "         " << std::right
+                  << std::setw(8) << stats.totals.assertions.passed << std::setw(8) << stats.totals.assertions.failed
+                  << std::setw(11) << std::fixed << std::setprecision(3) << duration_s << "s\n";
 
         for (size_t i = 1; i < wrappedName.size(); ++i) {
             std::cout << "  \033[90m↳ \033[0m" // Dim indent arrow
@@ -327,12 +347,12 @@ public:
             for (auto const &failure : m_currentFailures) {
                 std::cout << failure << '\n';
             }
-            std::cout << std::string(121, '-') << '\n';
+            std::cout << std::string(133, '-') << '\n';
         }
 
         m_testRunData.push_back(
-            {name, tagsStr, passed, stats.totals.assertions.passed, stats.totals.assertions.failed, m_currentFailures,
-             m_currentInfos}
+            {name, tagsStr, passed, stats.totals.assertions.passed, stats.totals.assertions.failed, duration_s,
+             m_currentFailures, m_currentInfos}
         );
 
         m_currentFailures.clear();
@@ -343,7 +363,7 @@ public:
     void testRunEnded(Catch::TestRunStats const &_testRunStats) override {
         StreamingReporterBase::testRunEnded(_testRunStats);
 
-        std::cout << std::string(121, '=') << '\n';
+        std::cout << std::string(133, '=') << '\n';
 
         auto const &tc = _testRunStats.totals.testCases;
         auto const &as = _testRunStats.totals.assertions;
@@ -444,7 +464,9 @@ private:
             html << "    </div>\n";
             html << "    <div class='stats'>\n";
             html << "      <span class='text-green'>&#10003; " << test.assertionsPassed << "</span> | ";
-            html << "      <span class='text-red'>&#10007; " << test.assertionsFailed << "</span>\n";
+            html << "      <span class='text-red'>&#10007; " << test.assertionsFailed << "</span> | ";
+            html << "      <span style='color: #34495e;'>&#8987; " << std::fixed << std::setprecision(3)
+                 << test.durationSeconds << "s</span>\n";
             html << "    </div>\n";
             html << "  </div>\n";