How to create a ds only on the upper surface in fenicsx

[Stein]

You’ll have to create a meshtags object where you tag that surface. Then you create a surface measure with that meshtags object attached:

ds = ufl.Measure('ds', domain=mesh, subdomain_data=surface_meshtags)

In your weak form, you’d use:

lasersource*testfunction*ds(1)

Assuming you’ve tagged that surface with value 1.

See this post from two hours ago

Eadg integral on part of the boundary

It should be like marker_value = 33 inner_facets = mesh.locate_entities_boundary(msh, 1, boundary_marker) facet_tags = mesh.meshtags(msh, 1, inner_facets, np.full(len(inner_facets), marker_value, dtype=np.int32)) ds = ufl.Measure("ds", domain=msh, subdomain_data=facet_tags, subdomain_id=marker_value)