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[Achim Schroll <question127166@xxxxxxxxxxxxxxxxxxxxx>]

New question #127166 on DOLFIN:
https://answers.launchpad.net/dolfin/+question/127166

Hi! 

Thanks for the new tutorial (aug 2010)!

Ultimately I need to specify a flux condition on a (small) part of the boundary as explained in Section 6.3. 
But, is it true that "it is not possible to perform integrals over different parts of the ... boundary using ... the VariationalProblem instance"?

Background: I am solving the nonlinear DEMOSTRAT model and want to model sediment inflow through a river bed.
Just recently, before the summer, I updated my code to implement the fully nonlinear system and to use DOLFINs features like automatic form building and nonlinearity. I don't want to go back to manual linearization etc...

Another detail:
Any idea what could be wrong when using the code on page 24 to evaluate the total flux:
n = FacetNormal(mesh)
flux = -dot(grad(u),n)*ds
total_flux = assemble(flux)
A runtime error appears: "Unable to extract mesh from form (no mesh found)" 
when executing the last line.
I am runing DOLFIN 0.9.7 under Ubuntu 9.10

Best, Achim
 

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