prolongation.h

#ifndef LF_USCALFE_PROLONGATION_H
#define LF_USCALFE_PROLONGATION_H
 
#include <lf/assemble/dofhandler.h>
#include <lf/fe/fe.h>
#include <lf/mesh/utils/utils.h>
#include <lf/refinement/mesh_function_transfer.h>
#include <lf/refinement/mesh_hierarchy.h>
 
namespace lf::fe {
 
template <typename SCALAR_COEFF, typename FES_COARSE, typename FES_FINE>
[[nodiscard]] Eigen::Matrix<SCALAR_COEFF, Eigen::Dynamic, 1> prolongate(
    const lf::refinement::MeshHierarchy &mh,
    std::shared_ptr<FES_COARSE> fespace_coarse,
    std::shared_ptr<FES_FINE> fespace_fine,
    const Eigen::Matrix<SCALAR_COEFF, Eigen::Dynamic, 1> &dofs_coarse,
    lf::base::size_type level_coarse) {
  // Assert that the FES_* are actually FE spaces
  using scalar_fe_coarse_t = typename FES_COARSE::Scalar;
  using scalar_fe_fine_t = typename FES_FINE::Scalar;
  static_assert(
      std::is_convertible_v<FES_COARSE &,
                            const ScalarFESpace<scalar_fe_coarse_t> &>,
      "Invalid coarse FE space provided");
  static_assert(std::is_convertible_v<FES_FINE &,
                                      const ScalarFESpace<scalar_fe_fine_t> &>,
                "Invalid fine FE space provided");
  // Obtain the dofhandlers from the fe spaces
  const lf::assemble::DofHandler &dofh_coarse{fespace_coarse->LocGlobMap()};
  const lf::assemble::DofHandler &dofh_fine{fespace_fine->LocGlobMap()};
  const lf::base::size_type N_coarse = dofh_coarse.NumDofs();
  // Assert correctness of inputs
  LF_ASSERT_MSG(
      level_coarse < mh.NumLevels() - 1,
      "level must not point to or beyond the finest mesh in the hierarchy");
  LF_ASSERT_MSG(
      dofs_coarse.size() >= N_coarse,
      "Too few basis function coefficients provided for coarse FE space");
  // Construct a mesh function to simplify the point evaluations
  const lf::fe::MeshFunctionFE mf_coarse(fespace_coarse, dofs_coarse);
  // Transfer the mesh function to the finer mesh
  const lf::refinement::MeshFunctionTransfer mf_fine(
      mh, mf_coarse, level_coarse, level_coarse + 1);
  // Return the nodal projection of this transferred mesh function
  return lf::fe::NodalProjection(*fespace_fine, mf_fine);
}
 
}  // namespace lf::fe
 
#endif  // LF_USCALFE_PROLONGATION_H