ffc team mailing list archive

[Anders Logg <logg@xxxxxxxxx>]

On Thu, Jan 28, 2010 at 10:03:57PM +0100, Kristian Oelgaard wrote:
>
>
> On 28 January 2010 21:59, Anders Logg <logg@xxxxxxxxx> wrote:
> >On Thu, Jan 28, 2010 at 09:56:18PM +0100, Kristian Oelgaard wrote:
> >>
> >>
> >>On 28 January 2010 21:14, Marie Rognes <meg@xxxxxxxxx> 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?
> >>
> >>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).
>
> Let's make it a new class then.
>
> Kristian

ok. I'll add a sketch but I'm not sure what should happen so I'll need
help filling out the details.

--
Anders

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