Dear Alexander,

On 24 Sep 2018, at 14:34, Terenin, Alexander <a.terenin17@imperial.ac.uk> wrote:

I have a Gmsh mesh which has physical points/curves/surfaces.

I need to create indicator functions for these that are equal to 1 for nodes in the given physical entity and zero everywhere else.

The tutorial https://www.firedrakeproject.org/demos/linear_fluid_structure_interaction.py... says that this can be done via

``` fn = Function(fnspace) par_loop( 'for (int i=0; i < f.dofs; i++) f[i][0] = 1.0;', dx(subdomain_id), {'f': (fn, WRITE)} ) ``

where subdomain_id is the numerical id of the physical entity in Gmsh.

Unfortunately, this only works for physical surfaces and not points or lines. The error I get is

``` File "firedrake/dmplex.pyx", line 1022, in firedrake.dmplex.get_cell_markers ValueError: Invalid subdomain_id 5 not in [3 4] ```

where 5 is a physical line, 1,2 are physical points, and 3,4 are physical surfaces.

Is there a different way I can create the necessary indicator function?

The example in the manual talks about creating a cell-based indicator function. But if I understand correctly, you also want a facet-based indicator function (the physical lines). This is possible by creating a space on the trace of the mesh: V = FunctionSpace(mesh, "DGT", 0) f = Function(V) but the kernel itself is slightly more involved. Can you explain a little more how you subsequently intend to use the indicator function? Perhaps there is no need for it. Lawrence