Anders Logg wrote: > On Fri, Jan 29, 2010 at 10:54:54AM +0000, Garth N. Wells wrote: >> >> Anders Logg wrote: >>> On Fri, Jan 29, 2010 at 10:31:05AM +0000, Garth N. Wells wrote: >>>> 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. >>> Yes, it should work for any order. I was just questioning the >>> usefulness of it if it results in standard P1 and P2 elements for >>> k = 1,2. >>> >>> Then I think I understand how it all works. >>> >>> But does the FFC demo make any sense? >> We have a demo? > > Yes, it's called ElementRestriction.ufl. :-) >
I've just changed it. It doesn't test extensively, but it does hopefully illustrate now better its purpose. On a related note, it would be useful if we could have multiple forms in one file and have all of them compiled. Can this be done already? Garth >>> Could we simplify it so that it >>> just defines a finite element restricted to a facet and then some dS >>> integral? >>> >> Sounds good. > > Could you post something simple and I'll add it. > >>> It currently breaks the code we added for RestrictedElement yesterday >>> because it has a complex nesting of restriction, then mixed with >>> another element and then restricted again. It looks like this is not >>> how you are using it in your solver. >>> >> The concept is very simple, so its implementation should be pretty >> simple too. > > Yes. > > -- > 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
