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).
