Ksagiyam/submesh core

[ksagiyam]

Enable cell submesh.

Depends on:

UFL

[pbrubeck]

I believe this key should not depend on the mesh. We just need to call finat once, independently of mt.terminal (and its domain).

[ksagiyam]

CoordinateMapping uses mt.terminal:

    @serial_cache(hashkey=make_basis_evaluation_key)
    def basis_evaluation(self, finat_element, mt, entity_id):
        return finat_element.basis_evaluation(mt.local_derivatives,
                                              self.point_set,
                                              (self.integration_dim, entity_id),
                                              coordinate_mapping=CoordinateMapping(mt, self))

[pbrubeck]

But internally it only cares about the element

[pbrubeck]

We should probably make CoordinateMapping only depend on the UFL element

[ksagiyam]

In concept that might be true, but we probably need refactoring. CoordinateMapping also has:

    def cell_size(self):
        return self.interface.cell_size(self.mt.restriction)

which implicitly depends on domain.

[ksagiyam]

Either way, as long as we pass mt to basis_evaluation, we need to use the entire mt in the cache key to ensure that we can safely use mt.something_new in the relevant parts of the code.