Divergence.h

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#pragma once
 
namespace ProcessLib
{
namespace Deformation
{
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