Anders Logg wrote: > 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? >
I use it for functions that live on cell facets only. Nothing special is required for k <= 2, but it's needed for k > 2 to eliminate internal dofs. Garth > -- > Anders _______________________________________________ Mailing list: https://launchpad.net/~ffc Post to : [email protected] Unsubscribe : https://launchpad.net/~ffc More help : https://help.launchpad.net/ListHelp
