feat(FieldDofMap): Completed FieldDofMap migration

also removed legacy BarotropicPolytrope implementation

libmeanfield/interface/field/field_mfem.cppm

@@ -5,6 +5,7 @@ module;
 #include <cstddef>
 #include <memory>
 #include <stdexcept>
+#include <utility>
 
 #include <mfem.hpp>
 
@@ -887,6 +888,110 @@ export namespace mean_field::field {
         mfem::Array<int> m_trueToReduced;
     };
 
+    /*
+     * Canonical adapter between an MFEM GridFunction and a reduced field
+     * vector.
+     *
+     * FieldDofMap deliberately contains only indexing information. This
+     * adapter binds that indexing to the exact finite-element space whose true
+     * DOFs the map describes. Consequently, a grid function from another
+     * finite-element space is rejected even when it happens to have the same
+     * vector size.
+     *
+     * The finite-element space must outlive the adapter.
+     */
+    class FieldDofGridFunctionAdapter {
+    public:
+        FieldDofGridFunctionAdapter(
+            FieldDofMap dofMap,
+            const mfem::FiniteElementSpace &finiteElementSpace
+        )
+            : m_dofMap(std::move(dofMap)),
+              m_finiteElementSpace(&finiteElementSpace) {
+            if (m_dofMap.full_size() != finiteElementSpace.GetTrueVSize()) {
+                throw std::invalid_argument(
+                    "FieldDofGridFunctionAdapter map and finite-element "
+                    "space have incompatible true-DOF sizes."
+                );
+            }
+        }
+
+        [[nodiscard]]
+        const FieldDofMap &dof_map() const noexcept {
+            return m_dofMap;
+        }
+
+        [[nodiscard]]
+        const mfem::FiniteElementSpace &finite_element_space() const noexcept {
+            return *m_finiteElementSpace;
+        }
+
+        /*
+         * Gather the grid function's true DOFs into reduced field ordering.
+         * The output vector is not resized so MFEM vector views remain valid.
+         */
+        void gather(
+            const mfem::GridFunction &gridFunction,
+            mfem::Vector &reduced
+        ) const {
+            validate_grid_function(gridFunction);
+
+            mfem::Vector full;
+            gridFunction.GetTrueDofs(full);
+            m_dofMap.gather(full, reduced);
+        }
+
+        [[nodiscard]]
+        mfem::Vector gather(const mfem::GridFunction &gridFunction) const {
+            mfem::Vector reduced(m_dofMap.reduced_size());
+            gather(gridFunction, reduced);
+            return reduced;
+        }
+
+        /*
+         * Scatter with projection semantics. Unsupported true DOFs are zeroed
+         * before the complete true vector is distributed to the grid function.
+         */
+        void scatter(
+            const mfem::Vector &reduced,
+            mfem::GridFunction &gridFunction
+        ) const {
+            validate_grid_function(gridFunction);
+
+            const mfem::Vector full = m_dofMap.scatter(reduced);
+            gridFunction.SetFromTrueDofs(full);
+        }
+
+        /*
+         * Scatter while preserving the grid function's existing unsupported
+         * true DOFs.
+         */
+        void scatter_into(
+            const mfem::Vector &reduced,
+            mfem::GridFunction &gridFunction
+        ) const {
+            validate_grid_function(gridFunction);
+
+            mfem::Vector full;
+            gridFunction.GetTrueDofs(full);
+            m_dofMap.scatter_into(reduced, full);
+            gridFunction.SetFromTrueDofs(full);
+        }
+
+    private:
+        void validate_grid_function(const mfem::GridFunction &gridFunction) const {
+            if (gridFunction.FESpace() != m_finiteElementSpace) {
+                throw std::invalid_argument(
+                    "FieldDofGridFunctionAdapter received a grid function "
+                    "from a different finite-element space."
+                );
+            }
+        }
+
+        FieldDofMap m_dofMap;
+        const mfem::FiniteElementSpace *m_finiteElementSpace;
+    };
+
     /*
      * Construct the canonical solver map for a registered spatial field.
      *
@@ -903,4 +1008,16 @@ export namespace mean_field::field {
 
         return FieldDofMap(support);
     }
+
+    template <
+        MfemDomainField FieldT,
+        utils::domain::IsSchema SchemaT>
+    [[nodiscard]]
+    FieldDofGridFunctionAdapter
+    make_field_dof_grid_function_adapter(const mfem::ParFiniteElementSpace &finiteElementSpace) {
+        return FieldDofGridFunctionAdapter(
+            make_field_dof_map<FieldT, SchemaT>(finiteElementSpace),
+            finiteElementSpace
+        );
+    }
 } // namespace mean_field::field