On Thu, Jan 28, 2010 at 09:56:18PM +0100, Kristian Oelgaard wrote: > > > On 28 January 2010 21:14, Marie Rognes <[email protected]> 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? > > Yes, that would be one option and we already have MixedElement and > RestrictedElement is much the same thing (we should change the name in UFL). > Although, one objective of this re-write of FFC was to remove as much as > possible w.r.t. FiniteElement. > > We could make the RestrictedElement a child class of FIAT.FiniteElement, that > should be OK since FFC uses FIAT as the backend for finite elements. Then we > just need to modify a few member functions.
I think Marie's suggestion is cleaner with a the RestrictedElement class (or whatever it will be named) *has* an element. That element could perhaps be another mixed element. There are not that many functions to implement (about 8). -- Anders
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