ffc team mailing list archive

[Anders Logg <logg@xxxxxxxxx>]

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?

--
Anders

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