On Tue, Sep 28, 2010 at 08:50:53AM -0700, Johan Hake wrote: > On Tuesday September 28 2010 05:34:06 Achim Schroll wrote: > > 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"? > > This should be possible. Just pass a FacetFunction which marks the different > Boundary domains, as the exterior_facet_domains. > > Can you point me to the tutorial. I think I do not have the latest copy.
It's available from http://www.fenics.org/doc/ > > 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. > > This because the dolfin::Form which is used to pass the ufc::form to the > assembler only chech the FunctionSpaces of the Test and TrialSpaces for a > mesh. So you need to pass this manually by: > > total_flux = assemble(flux, mesh=mesh) > > I think it would be convinient to be able to assemble a scalar from a > Function. The mesh is contained in the FunctionSpace so it should be possible. > I then need to figure out if a GenericFunction is a Function or an Expression. > Maybe we can add a has_function_space() method to the GenericFunction > interface? Sounds ok to me. -- Anders _______________________________________________ Mailing list: https://launchpad.net/~dolfin Post to : dolfin@lists.launchpad.net Unsubscribe : https://launchpad.net/~dolfin More help : https://help.launchpad.net/ListHelp
