On Wed, Aug 13, 2008 at 09:20:17PM +0000, Jed Brown wrote: > On Wed 2008-08-13 18:31, [EMAIL PROTECTED] wrote: > > > > > Kent-Andre Mardal wrote: > > >> BTW: the Assembler code that computes A, b and enforces BC > > >> simultaneously in a symmetric way, > > > > > > Very nice. We can now implement some symmetric linear solvers. > > > > > > Do you keep the 'Dirichlet' dofs and zero the row and column, or do you > > > eliminate them from the global system? > > > > The Dirichlet dofs are kept. I thought that was simplest to do.. > > It is certainly more work at this stage, but there are significant > benefits to actually removing the degrees of freedom. In particular, it > allows more preconditioners to be effective and makes related matrices > (i.e. the Schur complement) better conditioned. > > Jed
Do you have any numbers/references to support this? I was under the impression it didn't matter that much. It would be a complication to remove dofs (and then put them back in). There may be an elegant solution, but it would break the simple A = assemble(a, mesh) b = assemble(L, mesh) solve(A, u.vector(), b) -- Anders
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