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// ```text
// Copyright (C) 2022 Igor A. Baratta and Massimiliano Leoni
// This file is part of DOLFINx (https://www.fenicsproject.org)
// SPDX-License-Identifier: LGPL-3.0-or-later
// ```
// # Interpolation different meshes
#include <basix/e-lagrange.h>
#include <dolfinx/fem/dolfinx_fem.h>
#include <dolfinx/io/ADIOS2Writers.h>
#include <dolfinx/mesh/generation.h>
#include <bit>
#include <memory>
using namespace dolfinx;
using T = double;
int main(int argc, char* argv[])
{
init_logging(argc, argv);
MPI_Init(&argc, &argv);
{
MPI_Comm comm = MPI_COMM_WORLD;
// Create a tetrahedral mesh
auto mesh_tet = std::make_shared<mesh::Mesh<double>>(
mesh::create_box(comm, {{{0, 0, 0}, {1, 1, 1}}}, {20, 20, 20},
mesh::CellType::tetrahedron));
// Create a hexahedral mesh
auto mesh_hex = std::make_shared<mesh::Mesh<double>>(
mesh::create_box(comm, {{{0, 0, 0}, {1, 1, 1}}}, {15, 15, 15},
mesh::CellType::hexahedron));
basix::FiniteElement element_tet = basix::element::create_lagrange<double>(
mesh::cell_type_to_basix_type(mesh_tet->topology()->cell_type()), 1,
basix::element::lagrange_variant::equispaced, false);
auto V_tet = std::make_shared<fem::FunctionSpace<double>>(
fem::create_functionspace(mesh_tet, element_tet,
std::vector<std::size_t>{3}));
basix::FiniteElement element_hex = basix::element::create_lagrange<double>(
mesh::cell_type_to_basix_type(mesh_hex->topology()->cell_type()), 2,
basix::element::lagrange_variant::equispaced, false);
auto V_hex = std::make_shared<fem::FunctionSpace<double>>(
fem::create_functionspace(mesh_hex, element_hex,
std::vector<std::size_t>{3}));
auto u_tet = std::make_shared<fem::Function<T>>(V_tet);
auto u_hex = std::make_shared<fem::Function<T>>(V_hex);
auto fun = [](auto x) -> std::pair<std::vector<T>, std::vector<std::size_t>>
{
std::vector<T> fdata(3 * x.extent(1), 0.0);
using dextent = MDSPAN_IMPL_STANDARD_NAMESPACE::dextents<std::size_t, 2>;
MDSPAN_IMPL_STANDARD_NAMESPACE::mdspan<double, dextent> f(fdata.data(), 3,
x.extent(1));
for (std::size_t i = 0; i < x.extent(1); ++i)
{
f(0, i) = std::cos(10 * x(0, i)) * std::sin(10 * x(2, i));
f(1, i) = std::sin(10 * x(0, i)) * std::sin(10 * x(2, i));
f(2, i) = std::cos(10 * x(0, i)) * std::cos(10 * x(2, i));
}
return {std::move(fdata), {3, x.extent(1)}};
};
// Interpolate an expression into u_tet
u_tet->interpolate(fun);
// Interpolate from u_tet to u_hex
auto cell_map
= mesh_hex->topology()->index_map(mesh_hex->topology()->dim());
assert(cell_map);
std::vector<std::int32_t> cells(
cell_map->size_local() + cell_map->num_ghosts(), 0);
std::iota(cells.begin(), cells.end(), 0);
geometry::PointOwnershipData<T> interpolation_data
= fem::create_interpolation_data(
u_hex->function_space()->mesh()->geometry(),
*u_hex->function_space()->element(),
*u_tet->function_space()->mesh(), std::span(cells), 1e-8);
u_hex->interpolate(*u_tet, cells, interpolation_data);
#ifdef HAS_ADIOS2
// Adios2 is not well tested on big-endian systems, so skip them
if constexpr (std::endian::native != std::endian::big)
{
io::VTXWriter<double> write_tet(mesh_tet->comm(), "u_tet.bp", {u_tet});
write_tet.write(0.0);
io::VTXWriter<double> write_hex(mesh_hex->comm(), "u_hex.bp", {u_hex});
write_hex.write(0.0);
}
#endif
}
MPI_Finalize();
return 0;
}
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