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[Phil Marinier <question95908@xxxxxxxxxxxxxxxxxxxxx>]

Question #95908 on DOLFIN changed:
https://answers.launchpad.net/dolfin/+question/95908

    Status: Solved => Open

Phil Marinier is still having a problem:
So I just finished thinking through some of the consequences of not
being able to use vector valued Functions. I am trying to assign
gradients to a Neumann boundary condition. Basic I'm doing a domain
decomposition approach and I need to be able to calculate the gradients
after each iteration, average them out and reapply them as Neumann BCs
for the next iteration. I am also doing stuff on another boundary but
its all Dirichlet conditions. I defined my FunctionSpace and neumann
conditions like so:

element = FiniteElement("Lagrange", triangle, 1)

v = TestFunction(element)
u = TrialFunction(element)
f = Function(element)
g = Function(element)

a = inner(grad(v), grad(u))*dx
L = v*f*dx + v*g*ds(3)

where g is going to be my Neumann condition. In my code, I am currently
trying to assign a Function with 2 subfunctions (X and Y) to g

L.g = FunctionWith2SubFunctions

This should work, assuming the function with 2 subfunctions is defined
on the same FunctionSpace as L. But if I don't use vecotr values
elements, will dolfin know that the 2 SubFunctions are the X and Y
values? If my understanding of how things work is right, then dolfin
will get confused and either run wrong, or blow up.

Can I define 2 Neumann conditions, X and Y on the same boundary? If so
should I mark them differently? by this I mean should I do this:

L = v*f*dx + v*g*ds(2) + v*h*ds(3)

but mark the same boundary as both 2 and 3? Can this even be done in
dolfin?

Thank you for your help.

Phil

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