Question #109900 on DOLFIN changed: https://answers.launchpad.net/dolfin/+question/109900
Marie Rognes proposed the following answer: 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. -- 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
