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[Dominique <question122406@xxxxxxxxxxxxxxxxxxxxx>]

New question #122406 on DOLFIN:
https://answers.launchpad.net/dolfin/+question/122406

Hello,

In Python, I am trying to encapsulate a problem stated in weak form: a(v,u) = L(v) for all v in V (nonlinear or not). The first option that came to my mind is to use 

problem = VariationalProblem(a, L, bc)

Now I can do

A = assemble(a, mesh=mesh) ; b = assemble(L, mesh=mesh) ; bc.apply(A,b)

but I cannot do

A = assemble(problem.a, mesh=mesh) ; b = assemble(problem.L, mesh=mesh)

Somehow assemble() doesn't want to work on the members of 'problem'. It returns:

Unable to convert object to a UFL form: <dolfin.fem.form.Form; proxy of <Swig Object of type 'dolfin::Form *' at 0x99fa350> >
ERROR: An unexpected error occurred while tokenizing input
The following traceback may be corrupted or invalid
The error message is: ('EOF in multi-line statement', (4, 0))
[...]
UFLException: Unable to convert object to a UFL form: <dolfin.fem.form.Form; proxy of <Swig Object of type 'dolfin::Form *' at 0x99fa350> >

I don't *have* to use VariationalProblem to encapsulate the data, but I need to be able to get A and b somehow. I saw in a previous post that one could subclass NonlinearProblem. That would be fine for me, but I have 2 questions:

1) Is there a recommended way to encapsulate a and L so that they can be assemble()'d?

2) Could you please show an example usage of calling problem.F and problem.J when problem is a VariationalProblem? That just might answer the question.

Thanks in advance!
Dominique

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