On Mon, May 10, 2010 at 12:00:35PM -0000, Marie Rognes wrote: > 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?
Here: https://launchpad.net/fenics-doc -- Anders
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