> > > [EMAIL PROTECTED] wrote: >>> >>> [EMAIL PROTECTED] wrote: >>>>> [EMAIL PROTECTED] wrote: >>>>>>> One or more new changesets pushed to the primary dolfin repository. >>>>>>> A short summary of the last three changesets is included below. >>>>>>> >>>>>>> changeset: 4730:6548c25c33352492c9279c035509a139caab323b >>>>>>> tag: tip >>>>>>> user: "Garth N. Wells <[EMAIL PROTECTED]>" >>>>>>> date: Tue Sep 09 13:08:58 2008 +0100 >>>>>>> files: dolfin/fem/Assembler.cpp dolfin/pde/LinearPDE.cpp >>>>>>> description: >>>>>>> Revert to old assembly in LinearPDE due to bug in symmetric >>>>>>> assembly. >>>>>>> >>>>>>> There is a problem with exterior facets in the symmetric assembly. >>>>>>> The >>>>>>> code needs to be broken up to make debugging easier. >>>>>>> >>>>>> Agree that it should be broken up. But it will take some effort. >>>>>> Do you have an example where the bug is apparent ? >>>>>> >>>>> I was using a RT0 element (not one of the demos). It should be >>>>> reproducible by adding a non-zero Dirichlet bc (given be a Function) >>>>> to >>>>> the mixed-poisson demo. >>>>> >>>>> I had a quick look, but I couldn't find the problem, so I thought it >>>>> better to wait until the code is broken up. >>>>> >>>>> Garth >>>>> >>>> Strange, I see no reason for this not to work. >>>> (since the code involving only cell integrals is pretty clean, but >>>> ...) >>>> >>>> Anyway, I noticed that with my setup, CG is used. CG can not be used >>>> in this case since the problem is not positive. Did you use CG ? >>> No, I used an LU solver. I first noticed the problem when the LU >>> solvers >>> return a message that the system was singular. I only looked at the >>> computation of the RHS vector which was zero when it shouldn't have >>> been. >> >> Ok, and I guess the system is singular unless you have a mix of >> essential >> and natural >> bc. But the rhs should not be zero. >> > > The essential bcs appear in the form for this problem, so the assembler > shouldn't be doing anything extra for the bcs (bcs.size() = 0 in > Asssembler.cpp). Makes the bug rather strange. > > Garth >
So the essential bc that you refer to is the essential bc for the classical Poisson problem which ends up as natural in the mixed formulation. So you have something like: L = w*f*dx + w*g*ds I'll have a look. (But as already said, I completely agree on breaking up) Kent _______________________________________________ DOLFIN-dev mailing list [email protected] http://www.fenics.org/mailman/listinfo/dolfin-dev
