On Wed, Jun 04, 2014 at 11:02:53AM +0200, Martin Sandve Alnæs wrote:
> I see that facet_normals has been added as an argument to
> custom_integral::tabulate_tensor. If you actually want to use FacetNormal with
> custom integrals, I think the better way is to have custom_integral and
> custom_facet_integral, with the latter taking 'int facet' just like
> exterior_facet_integral, referring to the first cell. That will allow any 
> facet
> related geometric quantity to be computed just as for other facet integrals.

The failing on the next buildbot is not because facet normals were
added in UFC, but because a change in UFL allowing custom integrals to
use facet normals got lost in the merge. I pushed a fix earlier and it
should soon be green.

Regarding adding custom_facet_integral, it's not enough to send in an
int for the facet because the facet in question may not be a facet of
any of the cells in the list. It is something that only the assembler
knows about.

The signature of custom_integral allows sending in an arbitrary number
of cells (not just two), a list of quadrature points (which may or may
not be on a facet, just some arbitrary subset of the intersection of
the cells), and the value of the facet normal (if any) at each of the
quadrature points (the normal may be different for different
quadrature points).

This allows for integrating along a surface cutting arbitrarily
through an arbitrary number of overlapping cells.

> On a related note, the num_cells metadata hack should be made to fit with
> development of domain representation in ufl.

Yes. This is something I want to discuss with you when I have thought
more about how to polish up the interface for custom
integrals/multimesh.

--
Anders
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