Transfer of boundary tags in new version

dolfinx
1

Hi there,

I have a question related to the new dolfinx.mesh.EntityMap in version 0.10.
I used the old entity maps (np.arrays) in order to transfer for various mesh/facet-tags, e.g. for transferring boundary tags which declare mixed boundary conditions. For that I used in 0.9 something like

def get_boundary_marker_for_submesh(
    global_mesh: dfx.mesh.Mesh,
    global_boundary_tag: dfx.mesh.MeshTags,
    boundary_tag_values: Iterable[int],
    submesh: dfx.mesh.Mesh,
    enitity_map: np.ndarray,
    vertex_map: np.ndarray,
):
    transfered_global_tag, face_map = transfer_meshtags_to_submesh(global_mesh, global_boundary_tag, submesh, vertex_map, enitity_map)
    fdim = global_mesh.topology.dim -1
    num_faces_submesh = submesh.topology.index_map(fdim).size_local
    new_boundary_marker = np.zeros(num_faces_submesh, dtype=np.int32)
    new_tag_value = max(boundary_tag_values) + 1

    all_boundary_faces = dfx.mesh.exterior_facet_indices(submesh.topology)
    new_boundary_marker[all_boundary_faces] = new_tag_value
    for value in boundary_tag_values:
        boundary_i = transfered_global_tag.find(value)
        new_boundary_marker[boundary_i] = value
    submesh_boundary_tags = dfx.mesh.meshtags(submesh, fdim, np.arange(num_faces_submesh, dtype=np.int32), new_boundary_marker)
    return submesh_boundary_tags

which additionally marks the “inner” boundary of the submesh. The function `transfer_meshtags_to_submesh` is more or less a slight adaptation of the method I found here (It is in fact quite long, so please excuse that I dont just copy it here. I thought I’d rather give you the original source).
I understand that dolfinx.mesh.EntityMap is now in version 0.10 a two-way mapping between submesh entities and the global ones.

My questions are now the following:

  • How can I access the size of an entity map and loop over the values (similar as I would do over an array)?
  • Is there a quick way to port the function `transfer_meshtags_to_submesh` to version 0.10.?
  • And otherwise, do you have some advice how to write a similar function using the new dolfinx.mesh.EntityMap?

Thanks in advance :slight_smile:

2

See for instance:

that works with both the old and new EntityMap.

You can see the implementation here:

1 Like
3

Thank you a lot for the quick response, that was exactly what I was looking for.

Just to add on that for others, who might stumble over this and wonder how to get the numpy array:

cell_index_map = submesh.topology.index_map(dim)
num_cells_local = cell_index_map.size_local + cell_index_map.num_ghosts 
np_cell_map = cell_map.sub_topology_to_topology(
    np.arange(num_cells_local), inverse=False
)