From 48bc7d54726cd3772f8ab5fec23deff66adcc25e Mon Sep 17 00:00:00 2001
From: Emily Boudreaux <thomas@boudreauxmail.com>
Date: Mon, 2 Nov 2026 10:06:47 -0500
Subject: [PATCH] feat(dimensions): added second partial type and new
 dimensions

---
 src/include/serif/dimensions/dimensions.hpp | 34 ++++++++++++++++++++-
 src/include/serif/dimensions/partial.hpp    | 18 ++++++++++-
 src/include/serif/dimensions/type_alias.hpp |  3 +-
 3 files changed, 52 insertions(+), 3 deletions(-)

diff --git a/src/include/serif/dimensions/dimensions.hpp b/src/include/serif/dimensions/dimensions.hpp
index 060251a1..ccb804b5 100644
--- a/src/include/serif/dimensions/dimensions.hpp
+++ b/src/include/serif/dimensions/dimensions.hpp
@@ -64,6 +64,28 @@ namespace serif::dimensions {
         static constexpr std::string_view identifier = "inverse_time_squared";
     };
 
+    /**
+     * @brief Mass density divided by time,
+     */
+    struct MassDensityRate final : PhysicalQuantity {
+        static constexpr std::string_view identifier = "mass_density_rate";
+    };
+
+    /**
+     * @brief Force per unit volume
+     */
+    struct ForceDensity final : PhysicalQuantity {
+        static constexpr std::string_view identifier = "force_density";
+    };
+
+    /**
+     * @brief Pressure divided by length squared
+     */
+    struct PressureLaplacian final : PhysicalQuantity
+    {
+        static constexpr std::string_view identifier = "pressure_laplacian";
+    };
+
     /**
      * @struct GravitationalConstant
      *
@@ -200,6 +222,11 @@ namespace serif::dimensions {
         static constexpr std::string_view identifier = "specific_enthalpy";
     };
 
+    /** @brief The barotropic pressure primitive A with dA/density = (dP/density)/density. */
+    struct BarotropicPressurePotential final : ThermodynamicQuantity {
+        static constexpr std::string_view identifier = "barotropic_pressure_potential";
+    };
+
     /**
      * @struct EnergyDensity
      *
@@ -254,6 +281,11 @@ namespace serif::dimensions {
         static constexpr std::string_view identifier = "angular_velocity";
     };
 
+    /** @brief Angular acceleration, distinct from angular velocity despite sharing its chosen axis. */
+    struct AngularAcceleration final : PhysicalQuantity {
+        static constexpr std::string_view identifier = "angular_acceleration";
+    };
+
     /**
      * @struct Momentum
      *
@@ -364,4 +396,4 @@ namespace serif::dimensions {
     struct MagneticFluxDensity final : PhysicalQuantity {
         static constexpr std::string_view identifier = "magnetic_flux_density";
     };
-}
\ No newline at end of file
+}
diff --git a/src/include/serif/dimensions/partial.hpp b/src/include/serif/dimensions/partial.hpp
index ffff99b6..5acf9bce 100644
--- a/src/include/serif/dimensions/partial.hpp
+++ b/src/include/serif/dimensions/partial.hpp
@@ -27,6 +27,22 @@ namespace serif::dimensions {
     template <ThermodynamicQuantityType Quantity>
     struct WithRespectTo final {};
 
+    /** @brief
+     * A second EOS partial retains both differentiation quantities in its type.
+     */
+    template <ThermodynamicQuantityType OutputQuantity, ThermodynamicQuantityType FirstInput, ThermodynamicQuantityType SecondInput>
+    class SecondPartialDerivative final {
+    public:
+        /** @brief Store an explicitly evaluated second partial; this type does not differentiate. */
+        explicit constexpr SecondPartialDerivative(double value) noexcept : m_value(value) {}
+
+        /** @brief Return the numeric partial in the caller's physical units. */
+        [[nodiscard]] constexpr double value() const noexcept { return m_value; }
+
+    private:
+        double m_value;
+    };
+
     /**
      * @class PartialDerivative
      *
@@ -188,4 +204,4 @@ namespace serif::dimensions {
     private:
         double m_value; ///< Numeric value associated with the partial. If this is known at compile time then the compiler can optimize operations with partial.value() to be equivalent to compile time double operations.
     };
-}
\ No newline at end of file
+}
diff --git a/src/include/serif/dimensions/type_alias.hpp b/src/include/serif/dimensions/type_alias.hpp
index 6e588b41..caa6ef83 100644
--- a/src/include/serif/dimensions/type_alias.hpp
+++ b/src/include/serif/dimensions/type_alias.hpp
@@ -30,6 +30,7 @@ namespace serif::dimensions {
     using SpecificEnergyValue                            = QuantityValue<SpecificEnergy>;            ///< A quantity representing specific energy.
     using SpecificInternalEnergyValue                    = QuantityValue<SpecificInternalEnergy>;    ///< A quantity representing specific internal energy.
     using SpecificEnthalpyValue                          = QuantityValue<SpecificEnthalpy>;          ///< A quantity representing specific enthalpy.
+    using BarotropicPressurePotentialValue               = QuantityValue<BarotropicPressurePotential>; ///< A barotropic pressure primitive with specific energy units.
     using EnergyDensityValue                             = QuantityValue<EnergyDensity>;             ///< A quantity representing energy density.
     using GravitationalPotentialValue                    = QuantityValue<GravitationalPotential>;    ///< A quantity representing gravitational potential.
     using VelocityValue                                  = QuantityValue<Velocity>;                  ///< A quantity representing velocity.
@@ -48,4 +49,4 @@ namespace serif::dimensions {
     using DynamicViscosityValue                          = QuantityValue<DynamicViscosity>;          ///< A quantity representing dynamic viscosity.
     using KinematicViscosityValue                        = QuantityValue<KinematicViscosity>;        ///< A quantity representing kinematic viscosity.
     using MagneticFluxDensityValue                       = QuantityValue<MagneticFluxDensity>;       ///< A quantity representing magnetic flux density.
-}
\ No newline at end of file
+}