perf(allocations): reduced overall allocations by 95%, increaseed jacobian applicatin by 2x

This commit uses global pre allocated work space to dramatically reduce memory usage and allocation time

libmeanfield/impl/operators/prepared_stellar_equilibrium.cpp

@@ -1068,6 +1068,29 @@ namespace mean_field::operators {
         return m_generatedVolumeDisplacement;
     }
 
+    void PreparedStellarEquilibriumOperator::BuildVolumeDisplacementDirection(
+        const mfem::Vector &surfaceDeformationDirection,
+        mfem::Vector &volumeDisplacementDirection
+    ) const {
+        VerifyPrepared();
+        MFEM_VERIFY(
+            surfaceDeformationDirection.Size() == m_domainDeformation.parameterCount(),
+            "PreparedStellarEquilibriumOperator received a surface-deformation direction with the wrong size."
+        );
+        validate_finite_vector(
+            surfaceDeformationDirection,
+            "PreparedStellarEquilibriumOperator received a non-finite surface-deformation direction."
+        );
+        MFEM_VERIFY(
+            volumeDisplacementDirection.Size() == m_domainDeformation.volumeDisplacementSize(),
+            "PreparedStellarEquilibriumOperator received a volume-displacement workspace with the wrong size."
+        );
+
+        m_domainDeformation.applyJacobian(
+            m_surfaceDeformationParameters, surfaceDeformationDirection, volumeDisplacementDirection
+        );
+    }
+
     const mfem::Vector &PreparedStellarEquilibriumOperator::GetFullMechanicalResidual() const {
         VerifyPrepared();
         return m_fullMechanicalResidual;