Possible Bug in mesh refinement

dokken · June 11, 2026, 1:43pm

The parent_cells and parent_facets has a slightly different meaning than you think, see:

and

github.com/FEniCS/dolfinx

Parent cells not correct in refine_plaza

opened 12:47PM - 06 Jul 24 UTC

closed 01:51PM - 06 Jul 24 UTC

jorgensd

### Summarize the issue Reported at: https://fenicsproject.discourse.group/t…/mesh-refinement-using-dolfinx-mesh-refine-plaza/15168/4 ### How to reproduce the bug Run the following ### Minimal Example (Python) ```Python from mpi4py import MPI import numpy as np import dolfinx msh_c = dolfinx.mesh.create_unit_square(MPI.COMM_WORLD, 2, 2) msh_c.topology.create_entities(1) msh_f, parent_cells, _ = dolfinx.mesh.refine_plaza(msh_c, redistribute=False, option=dolfinx.mesh.RefinementOption.parent_cell) child_vertices = dolfinx.mesh.entities_to_geometry(msh_f, 2, np.arange(len(parent_cells), dtype=np.int32)) parent_vertices = dolfinx.mesh.entities_to_geometry(msh_c, 2, parent_cells) for i, (child_vertex, parent_vertex) in enumerate(zip(child_vertices, parent_vertices)): print(f"Child {i} has parent {parent_cells[i]}") child_vertex_coords = msh_f.geometry.x[child_vertex] print(f"Child {i} has vertices {child_vertex} at {child_vertex_coords}") parent_vertex_coords = msh_c.geometry.x[parent_vertex] print(f"Parent {parent_cells[i]} has vertices {parent_vertex} at {parent_vertex_coords}") num_cells = msh_c.topology.index_map(msh_c.topology.dim).size_local marker = np.arange(num_cells, dtype=np.int32) ct = dolfinx.mesh.meshtags(msh_c, msh_c.topology.dim, marker, marker) ct_refined = dolfinx.mesh.meshtags(msh_f, msh_f.topology.dim, np.arange(len(parent_cells), dtype=np.int32), parent_cells) with dolfinx.io.XDMFFile(msh_c.comm, "ct.xdmf", "w") as xdmf: xdmf.write_mesh(msh_c) xdmf.write_meshtags(ct, msh_c.geometry) with dolfinx.io.XDMFFile(msh_f.comm, "ct_refined.xdmf", "w") as xdmf: xdmf.write_mesh(msh_f) xdmf.write_meshtags(ct_refined, msh_f.geometry) ``` ### Output (Python) _No response_ ### Version main branch ### DOLFINx git commit _No response_ ### Installation _No response_ ### Additional information ![image](https://github.com/FEniCS/dolfinx/assets/8554300/bff91966-f09f-491a-8d0e-1a1fa07accc2)

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Possible Bug in mesh refinement

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