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? -- Anders -- 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
