How to define boundary conditions on an irregular geometry?

[dokken]

For more complicated geometries , its common to use external software, like gmsh/pygmsh. With these softwares, you can set physical markers for cells snd facets, Which can be loaded into dolfin as described here:

Transitioning from mesh.xml to mesh.xdmf, from dolfin-convert to meshio

This can be done using meshio and writing the explicit data to xdmf file. import meshio msh = meshio.read("test.msh") meshio.write("mesh.xdmf", meshio.Mesh(points=msh.points, cells={"tetra": msh.cells["tetra"]})) meshio.write("mf.xdmf", meshio.Mesh(points=msh.points, cells={"triangle": msh.cells["triangle"]}, cell_data={"triangle": {"name_to_read": msh.cell_data["triangle"]["gmsh:physical"]}})) from dolfin import * mesh = Mesh() with XDMFFile("mesh.xdmf") …