Change the value of meshtags in a loop

dolfinx
,
1

Hi,
I am update my code from fenicsx-0.6.0 to fenicsx-0.8.0. I find that the update of meshtags function makes the values read only. However, in my previous code, I defined a meshtag and changed its values in my loop, like the demo:

import os
os.environ['OMP_NUM_THREADS'] = '1'
from mpi4py import MPI
comm = MPI.COMM_WORLD
import numpy as np
from dolfinx import mesh

msh             = mesh.create_unit_square(MPI.COMM_WORLD, 96, 96, mesh.CellType.triangle)
num_cells       = msh.topology.index_map(msh.topology.dim).size_local + msh.topology.index_map(msh.topology.dim).num_ghosts
indices         = np.arange(num_cells).astype(np.int32)
values          = np.full(indices.shape, 1, dtype=np.intc) 
meshtag         = mesh.meshtags(msh, msh.topology.dim, indices, values)
for i in range(0,5):
    meshtag.values[:] = np.full(indices.shape, i, dtype=np.intc)

This works fine in fenicsx-0.6.0. But when I run the code in fenicsx-0.8.0, it returns the error.

ValueError: assignment destination is read-only
    meshtag.values[:] = np.full(indices.shape, i, dtype=np.intc)

I also tried

for i in range(0,5):
    meshtag._cpp_object.values[:] = np.full(indices.shape, i, dtype=np.intc)

but the error is the same. Although I have lots of other ways instead to implement my algorithm, I still would like to know that is there any way to change this value as in fenicsx-0.6.0?

2

That probably changed when we moved to nanobind. The simplest workaround is to create a new dolfinx.fem.meshtags, rather than trying to update the values in-place.