Dear all,

I would like to mark the boundary of the subdomain, which is not the boundary of the entire domain. How can I achieve that?

I have tried below but it does not work

```
parameters['reorder_dofs_serial'] = False
x0, y0 = 10, 10 ### computational domain size
center_1 = np.array([-3.5, -4]) ### center of the hole domain
radius_1 = 0.5 ### radius of the hole domain
center_2 = np.array([3.5, 4])
radius_2 = 0.5
domain = Rectangle(Point(-x0,-y0),Point(x0,y0))
hole_1 = Circle(Point(center_1[0],center_1[1]),radius_1)
hole_2 = Circle(Point(center_2[0],center_2[1]),radius_2)
domain.set_subdomain(1, hole_1)
domain.set_subdomain(2, hole_2)
resol = 150 ### resolution of the mesh
mesh = generate_mesh(domain, resol) ### the FEM mesh
subdomains = MeshFunction('size_t',mesh,mesh.topology().dim(),mesh.domains()) ### subdomains data
n = FacetNormal(mesh) ### outward normal unit vector
V = FunctionSpace(mesh, "P", 1) ### Langrage base function is used
dx=Measure('dx',subdomain_data=subdomains)
submesh_hole_1 = SubMesh(mesh, subdomains,1)
submesh_hole_2 = SubMesh(mesh, subdomains,2)
############################################################################
### Define two subdomain boundaries separately
############################################################################
class interior_boundaries_1(SubDomain):
def inside(self,x,on_boundary):
return abs(sqrt((x[0]-center_1[0])**2+(x[1]-center_1[1])**2))-radius_1 <= mesh.hmin()
class interior_boundaries_2(SubDomain):
def inside(self,x,on_boundary):
return abs(sqrt((x[0]-center_2[0])**2+(x[1]-center_2[1])**2))-radius_2 <= mesh.hmin()
boundaries=MeshFunction('size_t',mesh, mesh.topology().dim() - 1)
boundaries.set_all(0)
interior_boundaries_1().mark(boundaries, 1)
interior_boundaries_2().mark(boundaries, 2)
ds=Measure('ds',subdomain_data=boundaries)
print(assemble(project(Constant(1), V) * ds(1))) ### expect pi but got 0.0
```

Actually, I was thinking to get the global index of the edges of the subdomain boundaries, then marking the boundaries manually, however, it does not recognize “parent_facet_indices”, while “parent_cell_indices” and “parent_vertex_indices” work well.

Any help is much appreciated!

Best,

Alice