It doesn’t make sense to use the method pointwise with a facet.
The method pointwise uses the fact that:
- In legacy dolfin, a degree of freedom has a corresponding coordinate in physical space.
- Method=pointwise checks if the coordinate of a dof matches some geometrical requirement.
The standard method; topological can do two things:
- given a facet, if finds all dofs associated with that facet and applies the boundary condition to them,
- given a subdomain (some expression that takes in the mesh coordinates and returns a true/false value) it checks if the vertices of the facets satisfies this criterion (it can also check the midpoint of the facet). If all of these satisfies the condition, all relate dofs has boundary conditions applied to them.