On 28 January 2010 21:59, Anders Logg <[email protected]> wrote:
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).
Let's make it a new class then. Kristian
-- Anders -----BEGIN PGP SIGNATURE----- Version: GnuPG v1.4.9 (GNU/Linux) iEYEARECAAYFAkth+roACgkQTuwUCDsYZdGO8wCfcCoNgO22AeHHGX9crxLkznt7 H4MAn0krAMrRmtTq3keqPazWWmRPqvdT =2ipj -----END PGP SIGNATURE-----
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