Merge branch 'DivergenceComputation' into 'master'

[PL/SDN] Move divergence computation

See merge request ogs/ogs!5213

ProcessLib/Deformation/Divergence.h

-/**
- * \file
- *
- * \copyright
- * Copyright (c) 2012-2025, OpenGeoSys Community (http://www.opengeosys.org)
- *            Distributed under a Modified BSD License.
- *              See accompanying file LICENSE.txt or
- *              http://www.opengeosys.org/project/license
- */
-
-#pragma once
-
-namespace ProcessLib
-{
-namespace Deformation
-{
-/// Divergence of displacement, the volumetric strain.
-template <int DisplacementDim, int NPOINTS, typename DNDX_Type>
-double divergence(
-    const Eigen::Ref<Eigen::Matrix<double, NPOINTS * DisplacementDim, 1> const>&
-        u,
-    DNDX_Type const& dNdx)
-{
-    double divergence = 0;
-    for (int i = 0; i < DisplacementDim; ++i)
-    {
-        divergence += dNdx.template block<1, NPOINTS>(i, 0) *
-                      u.template segment<NPOINTS>(i * NPOINTS);
-    }
-    return divergence;
-}
-}  // namespace Deformation
-}  // namespace ProcessLib

ProcessLib/SmallDeformationNonlocal/SmallDeformationNonlocalFEM.h

@@ -29,7 +29,6 @@
 #include "NumLib/Fem/ShapeMatrixPolicy.h"
 #include "ParameterLib/Parameter.h"
 #include "ProcessLib/Deformation/BMatrixPolicy.h"
-#include "ProcessLib/Deformation/Divergence.h"
 #include "ProcessLib/Deformation/LinearBMatrix.h"
 #include "ProcessLib/LocalAssemblerTraits.h"
 #include "ProcessLib/Utils/SetOrGetIntegrationPointData.h"
@@ -575,8 +574,9 @@ public:
             auto const& w = _ip_data[ip].integration_weight;
 
             double const div_u =
-                Deformation::divergence<DisplacementDim,
-                                        ShapeFunction::NPOINTS>(u, dNdx);
+                (dNdx.template topRows<DisplacementDim>() *
+                 u.reshaped(ShapeFunction::NPOINTS, DisplacementDim))
+                    .trace();
             crack_volume += div_u * d * w;
         }
     }