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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 14:22, Marie Rognes wrote:
> Garth Wells wrote:
>> 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?
>>
>
> "Real" (Space of real numbers)
>

OK.

It would good to add this example as a demo to DOLFIN.

Garth

>
> --
> Marie
>
>> 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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>>
>
>
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