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 <[email protected]>: > >>>> 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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