symmetrize the Cauchy Tensor

src/scheme/HyperelasticSolver.cpp

@@ -464,6 +464,8 @@ class HyperelasticSolverHandler::HyperelasticSolver final : public HyperelasticS
         new_u[j] += dt_over_Mj * momentum_fluxes;
         new_E[j] += dt_over_Mj * energy_fluxes;
         new_CG[j] += dt_over_Mj * cauchy_green_fluxes;
+        new_CG[j] += transpose(new_CG[j]);
+        new_CG[j] *= 0.5;
       });
 
     CellValue<const double> new_Vj = MeshDataManager::instance().getMeshData(*new_mesh).Vj();