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[Garth Wells <question109900@xxxxxxxxxxxxxxxxxxxxx>]

Question #109900 on DOLFIN changed:
https://answers.launchpad.net/dolfin/+question/109900

Garth Wells proposed the following answer:

On 06/05/10 13:52, 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.
>

Nice. What does 'R' stand for in the definition of the space Q?

Garth

> 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()
>
>
> --
> Marie
>
>
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