Anders Logg wrote: > On Fri, Jan 29, 2010 at 10:10:37AM +0000, Garth N. Wells wrote: > >>> Sub domains seem to be very different, but the other two cases just >>> seem to be a matter of some dofs being "active" and the other zeroed >>> out. This is what Marie suggested yesterday, that a restricted element >>> only considers a subset of the dofs of some given element. >>> >> Sounds good. >> >>> The thing I don't understand yet is the selection of which dofs should >>> be active. If we think of the case with restriction to facets, then >>> the element needs to be restricted to different facets depending on >>> which facet we are integrating over, or are we always mapping one >>> specific facet of the reference cell to the current facet? >>> >> It works the same way as the DG elements, just the internal dofs are >> thrown away, which is the latter if the above, right? >> >>> Say we have P1 elements in 2D which have 3 dofs. Then we could >>> restrict that element to the dofs on the first facet (facet 0). These >>> dofs are then labeled 1 and 2. But sometimes a facet in the mesh will >>> correspond to the edge between 0 and 1 or 0 and 2. >>> >> We don't restrict to individual facets, but to all facts of a cell. > > That makes sense, but one thing still confuses me. Say that we have a > P1 element and restrict it to facets. Then all dofs are on the facets > so the result of the restriction is just a new P1 element. Same for P2 > where the result again is a new P2 element.
Yes. > For P3, the result is P3 > element minus just one dof. Yes. > So does this make much difference for > other than very high degree elements? > It is only needed for k > 2. It's important because everything in FFC/UFL works for arbitrary orders. Garth > -- > Anders _______________________________________________ Mailing list: https://launchpad.net/~ffc Post to : ffc@lists.launchpad.net Unsubscribe : https://launchpad.net/~ffc More help : https://help.launchpad.net/ListHelp
