ffc team mailing list archive

[Anders Logg <logg@xxxxxxxxx>]

On Thu, Jan 28, 2010 at 08:28:22PM +0000, Garth N. Wells wrote:
>
>
> Anders Logg wrote:
> > On Thu, Jan 28, 2010 at 09:14:36PM +0100, Marie Rognes wrote:
> >> Kristian Oelgaard wrote:
> >>>
> >>> 2010/1/27 Medhi Nikbakht <m.nikbakht@xxxxxxxxxx>:
> >>>> On Wed, 2010-01-27 at 15:50 +0100, Marie Rognes wrote:
> >>>>> FFC compilation fails for
> >>>>>
> >>>>>    ElementRestriction.ufl
> >>>> The error message says that "ElementRestriction" is not supported by
> >>>> FIAT.
> >>>> How will the restricted elements be implemented? Wouldn't it be better
> >>>> to support them inside FFC?
> >>> There are two types of restrictions supported in UFL (and the old FFC).
> >>> 1) Restriction onto Measure (like 'dc'), which is what you want.
> >>> 2) Restriction onto Cell, as for instance restricting a Lagrange
> >>> element defined on a 'triangle' to its facets.
> >>>
> >>> The third restriction that we might want in the future is
> >>> restriction onto subdomains possible in UFL but not in FFC.
> >>>
> >>> To implement 1) I think it is enough to just attach the Measure as
> >>> a member to the fiat_element and the simply look for it in
> >>> appropriate places when generating the code. That means handle it
> >>> in FFC.fiatinterface, could that work?
> >>>
> >>> To implement 2) I modified the return value of entity_dofs() and
> >>> tabulate() accordingly. To do it this way again we will need to
> >>> make changes in FIAT_NEW.FiniteElement and FFC.MixedElement. I'm
> >>> not sure it is a good idea to make FIAT_NEW.PolynomialSet aware of
> >>> restrictions, but I don't know enough about the FIAT internals to
> >>> back up this claim.
> >>>
> >>
> >> How about adding a class RestrictedElement that contains an element
> >> and (based on the restriction)
> >> a list of relevant basis function indices, and overrides the methods
> >> as FiniteElement/MixedElement?
> >>
> >> No need to make FIAT aware of this.
> >
> > This sounds good. I think I understand (somewhat) what (2) is supposed
> > to do, but not (1).
> >
> > And as Garth suggests, I think a better name is FacetElement. Does a
> > FacetElement know that it can only be integrated over facets, not the
> > interior, or can it?
> >
>
> It's possible that it could be integrated over the interior, but
> probably not very sensible.
>
> I think that FacetElement is a bit misleading, since what it does is
> just take the dofs of a cell that live on the facets. With FacetElement
> I think of an element of topological dim 2 embedded in 3D.

I thought that was the idea.

Exactly what does it do?

--
Anders

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