On Tue, May 7, 2013 at 9:20 AM, Frederik Treue <frtr at fysik.dtu.dk> wrote:
> Hi, > > I may be overlooking something very obvious here, but: > > I'm trying to solve a convection-diffusion problem. The method I use > requires me to solve some Helmholtz and Poisson equations, which is the > time consuming part. In order to reduce this time, I try to use > preconditioners. However, no matter which preconditioner I use (I've > tried PCJACOBI,PCBJACOBI,PCPBJACOBI,PCMG with 2 levels, galerkin) it > introduces errors along the edges of the local domains when using > multiple processors. These errors are small, but they don't converge to > 0 as a function of resolution. I have checked with PCNONE, which > eliminates the problem, but becomes unbearably slow. > > Is this somehow unavoidable? Or am I making some silly mistake? The code > is somewhat complicated, but if desired, I can try to cook up a > proof-of-(non)concept. You have made a mistake somewhere, probably in your parallel function evaluation. For Poisson, see SNES ex5. Matt > > /Frederik Treue > > -- What most experimenters take for granted before they begin their experiments is infinitely more interesting than any results to which their experiments lead. -- Norbert Wiener -------------- next part -------------- An HTML attachment was scrubbed... URL: <http://lists.mcs.anl.gov/pipermail/petsc-users/attachments/20130507/488c23e2/attachment.html>
