Feature/netgen periodic meshes#5217
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When a Netgen mesh carries periodic identifications, ngsPETSc now produces a vertex-merged (periodic) DMPlex. This finishes the job on the Firedrake side: the Mesh() netgen branch detects periodicity, builds the intermediate topology without reordering, and attaches a discontinuous DG1 coordinate field (MeshGeometry._periodic_coordinates) carrying the un-wrapped geometry via _postprocess_periodic_mesh, exactly as Firedrake's own periodic meshes. Each Firedrake cell is matched to its Netgen element by geometry (hashing the wrapped per-cell coordinates), which is robust to reordering. The DG coordinate space uses the equispaced variant required by _set_dg_coordinates. High-order curving of periodic meshes raises NotImplementedError for now. Adds regression tests for a periodic square (one and two directions), a periodic cylinder, and the too-coarse error path. Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
Add a "Periodic Meshes" section to the Netgen integration demo showing how
to declare OCC periodic identifications and import the resulting mesh into
Firedrake. The worked example is the periodic-cylinder ("screw pinch")
reduced model of a tokamak: a cylinder whose two circular ends are
identified, making the axial (toroidal) direction periodic. It labels the
lateral wall, checks the geometry survives the vertex merge (volume 2*pi^2),
and solves a manufactured Helmholtz problem with Dirichlet data on the wall
and periodicity on the ends, demonstrating seam continuity. Also documents
the too-coarse ValueError and the degree==1 limitation.
Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
pbrubeck
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Jul 9, 2026
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| topology_reorder = False if netgen_periodic else reorder | ||
| topology = MeshTopology(plex, name=plex.getName(), reorder=topology_reorder, |
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| topology_reorder = False if netgen_periodic else reorder | |
| topology = MeshTopology(plex, name=plex.getName(), reorder=topology_reorder, | |
| reorder = False if netgen_periodic else reorder | |
| topology = MeshTopology(plex, name=plex.getName(), reorder=reorder, |
pbrubeck
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Jul 9, 2026
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| @PETSc.Log.EventDecorator() | ||
| def _periodic_coordinates(self, permutation_tol=1e-8): |
pbrubeck
reviewed
Jul 9, 2026
| # is finished off with a discontinuous coordinate field below. That field | ||
| # is built on the un-reordered topology (as for Firedrake's own periodic | ||
| # meshes), so suppress reordering here and reapply it in postprocessing. | ||
| netgen_periodic = len(netgen_firedrake_mesh.meshMap.ngMesh.GetIdentifications()) > 0 |
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Do as the comment says and supress reordering here. Remove the comment, we don't like AI slop
pbrubeck
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Jul 9, 2026
| # discontinuous coordinate field carrying the un-wrapped geometry. | ||
| if degree != 1: | ||
| raise NotImplementedError( | ||
| "High-order curving of periodic netgen meshes is not supported yet." |
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pbrubeck
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Jul 9, 2026
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| from firedrake.utility_meshes import _postprocess_periodic_mesh | ||
| permutation_tol = netgen_flags.get("permutation_tol", 1e-8) | ||
| coordinates = mesh._periodic_coordinates(permutation_tol=permutation_tol) | ||
| temp = _postprocess_periodic_mesh(coordinates, | ||
| mesh.comm, | ||
| distribution_parameters, | ||
| reorder, | ||
| name, | ||
| kwargs.get("distribution_name"), | ||
| kwargs.get("permutation_name")) | ||
| temp.netgen_mesh = mesh.netgen_mesh | ||
| temp.netgen_flags = mesh.netgen_flags | ||
| mesh = temp |
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create a helper function in netgen.py doing everything here
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ngsPETSc PR: NGSolve/ngsPETSc#124