feat(initial): added portable mfem build system

src/python/bindings.cpp

@@ -0,0 +1,91 @@
+#include <meson_mfem_template/config.hpp>
+#include <mfem.hpp>
+#include <nanobind/nanobind.h>
+#include <nanobind/stl/string.h>
+
+#include <cmath>
+#include <stdexcept>
+#include <string>
+
+namespace nb = nanobind;
+
+namespace
+{
+int serial_poisson_dofs(int cells, int order)
+{
+   if (cells < 2 || order < 1)
+   {
+      throw nb::value_error("cells must be >= 2 and order must be >= 1");
+   }
+   mfem::Mesh mesh = mfem::Mesh::MakeCartesian2D(
+      cells, cells, mfem::Element::QUADRILATERAL, true, 1.0, 1.0);
+   mfem::H1_FECollection elements(order, mesh.Dimension());
+   mfem::FiniteElementSpace space(&mesh, &elements);
+   mfem::Array<int> essential_boundary(mesh.bdr_attributes.Max());
+   essential_boundary = 1;
+   mfem::Array<int> essential_dofs;
+   space.GetEssentialTrueDofs(essential_boundary, essential_dofs);
+
+   mfem::ConstantCoefficient one(1.0);
+   mfem::LinearForm rhs(&space);
+   rhs.AddDomainIntegrator(new mfem::DomainLFIntegrator(one));
+   rhs.Assemble();
+   mfem::GridFunction solution(&space);
+   solution = 0.0;
+   mfem::BilinearForm diffusion(&space);
+   diffusion.AddDomainIntegrator(new mfem::DiffusionIntegrator(one));
+   diffusion.Assemble();
+
+   mfem::OperatorPtr matrix;
+   mfem::Vector linear_rhs;
+   mfem::Vector linear_solution;
+   diffusion.FormLinearSystem(
+      essential_dofs, solution, rhs, matrix, linear_solution, linear_rhs);
+   mfem::GSSmoother smoother(static_cast<mfem::SparseMatrix &>(*matrix));
+   mfem::CGSolver solver;
+   solver.SetOperator(*matrix);
+   solver.SetPreconditioner(smoother);
+   solver.SetRelTol(1e-10);
+   solver.SetMaxIter(200);
+   solver.SetPrintLevel(0);
+   solver.Mult(linear_rhs, linear_solution);
+   if (!solver.GetConverged())
+   {
+      throw std::runtime_error("MFEM CG solve did not converge");
+   }
+   return space.GetTrueVSize();
+}
+
+nb::dict capabilities()
+{
+   nb::dict result;
+   result["mpi"] = MESON_MFEM_HAS_MPI != 0;
+   result["hypre"] = MESON_MFEM_HAS_HYPRE != 0;
+   result["metis"] = MESON_MFEM_HAS_METIS != 0;
+   result["cuda"] = MESON_MFEM_HAS_CUDA != 0;
+   result["hip"] = MESON_MFEM_HAS_HIP != 0;
+   result["openmp"] = MESON_MFEM_HAS_OPENMP != 0;
+   result["gslib"] = MESON_MFEM_HAS_GSLIB != 0;
+   result["zlib"] = MESON_MFEM_HAS_ZLIB != 0;
+   result["sundials"] = MESON_MFEM_HAS_SUNDIALS != 0;
+   result["ceed"] = MESON_MFEM_HAS_CEED != 0;
+   result["fms"] = MESON_MFEM_HAS_FMS != 0;
+   result["algoim"] = MESON_MFEM_HAS_ALGOIM != 0;
+   result["simd"] = MESON_MFEM_HAS_SIMD != 0;
+   result["bundled_mfem"] = MESON_MFEM_USING_BUNDLED_MFEM != 0;
+   return result;
+}
+} // namespace
+
+NB_MODULE(_core, module)
+{
+   module.doc() = "Small nanobind validation module for the Meson MFEM bundle";
+   module.def("mfem_version", []() { return std::string(MFEM_VERSION_STRING); });
+   module.def("capabilities", &capabilities);
+   module.def(
+      "serial_poisson_dofs",
+      &serial_poisson_dofs,
+      nb::arg("cells") = 4,
+      nb::arg("order") = 2,
+      "Assemble and solve a small MFEM Poisson problem; return true DOFs.");
+}