I have a composite material having sphere-shaped particles as reinforcements. So, there will be two different materials, one for matrix and one for these spheres. How can I define the boundaries of the subdomain for these spheres? I’ve tried to get cell coordinates by `cell.get_coordinates_dofs`

, but I think it didn’t work (maybe I’m missing something).

I’m using pygmsh to create geometry and mesh:

```
height = 0.020
radius = 0.020
with pygmsh.occ.Geometry() as geom:
geom.characteristic_length_max=0.003 # smaller = more mesh elements
cyl = geom.add_cylinder([0.0, 0.0, 0.0], [0.0, 0.0, height], radius, mesh_size=1)
sphere_list=[]
# Place voids with 3mm radius in BCC configuration
for i in np.linspace(-0.015, 0.015, 4):
for j in np.linspace(-0.015, 0.015, 4):
for k in np.linspace(-0.005, 0.015, 3):
sphere_list.append(geom.add_ball([i, j, k], 0.003))
spheres=geom.boolean_union(sphere_list)
cyl==geom.boolean_difference(cyl,spheres)
mesh = geom.generate_mesh()
```