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. For P3, the result is P3 element minus just one dof. So does this make much difference for other than very high degree elements? -- Anders
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