Question #109900 on DOLFIN changed: https://answers.launchpad.net/dolfin/+question/109900
Marie Rognes posted a new comment: Marie Rognes wrote: > Anders Logg wrote: >> On Thu, May 06, 2010 at 08:42:19PM -0000, Marie Rognes wrote: >> >>> Question #109900 on DOLFIN changed: >>> https://answers.launchpad.net/dolfin/+question/109900 >>> >>> Marie Rognes proposed the following answer: >>> Anders Logg wrote: >>> >>>> Question #109900 on DOLFIN changed: >>>> https://answers.launchpad.net/dolfin/+question/109900 >>>> >>>> Anders Logg proposed the following answer: >>>> On Thu, May 06, 2010 at 02:52:33PM +0200, Marie Rognes wrote: >>>> >>>> >>>>> Achim Schroll wrote: >>>>> >>>>> >>>>>> New question #109900 on DOLFIN: >>>>>> https://answers.launchpad.net/dolfin/+question/109900 >>>>>> >>>>>> for a plain Poisson eqn with pure Neumann b.c., how to specify >>>>>> the scaling condition u*dx = 0 ? >>>>>> >>>>>> >>>>> If you have a recent dolfin, you can introduce a constant c acting >>>>> as a Lagrange multiplier corresponding to the constraint. See >>>>> example below. >>>>> >>>>> from dolfin import * >>>>> >>>>> mesh = UnitSquare(32, 32) >>>>> V = FunctionSpace(mesh, "CG", 1) >>>>> Q = FunctionSpace(mesh, "R", 0) >>>>> M = V * Q >>>>> >>>>> (u, c) = TrialFunctions(M) >>>>> (v, d) = TestFunctions(M) >>>>> >>>>> f = Expression("x[0]*x[1]*sin(pi*x[0])") >>>>> >>>>> a = dot(grad(v), grad(u))*dx + d*u*dx + c*v*dx >>>>> L = v*f*dx >>>>> >>>>> pde = VariationalProblem(a, L) >>>>> u_h = pde.solve() >>>>> >>>>> plot(u_h[0]) >>>>> interactive() >>>>> >>>>> >>>> But make sure to not name that space 'M' if you try this with a UFL >>>> file or you will get a strange error (since 'M' is reserved in form >>>> files). >>>> >>>> Anyway, I'm wondering about the dofmap for the "R" element. It sets >>>> _global_dimension to m.num_entities[2] which is the global number of >>>> cells, but then it maps all dofs to 0. Is that right? Shouldn't the >>>> global dimension be 1? >>>> >>>> >>>> >>> Yes, it is a bug for non-mixed elements(!). I noticed but didn't really >>> want to start fixing before >>> the weekend. It's on the todo-list though. >>> >> >> ok! I thought I might have missed the point but then I think I know >> what's going on. Very cool feature. >> >> > > It is a true hack that I added for testing purposes. But it seems > useful, so let's keep it. I'll clean it up a bit (and fix that bug.) > >> Btw, you can add that demo now. ;-) >> > > Great. Added. Where should I put documentation? -- Marie -- You received this question notification because you are a member of DOLFIN Team, which is an answer contact for DOLFIN. _______________________________________________ Mailing list: https://launchpad.net/~dolfin Post to : [email protected] Unsubscribe : https://launchpad.net/~dolfin More help : https://help.launchpad.net/ListHelp
