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. -- 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
