Thank you both. The solvers are the same, I double checked that. It could be the case that the type of partitioning plays a role here, since i'm indeed using a DA. However, why is it that for example a run on 2 processors the number of iterations is higher than on 8? Both use DA-partitioning in this case. To specify subdomains manually, where do i start?
Leo 2010/9/23 Jed Brown <jed at 59a2.org> > The latter is using the partition provided by the DA (or user) which looks > to be better than the one computed in the serial run. If you have Parmetis, > then it will be used by PCBJACOBI, otherwise the partition is naive. You can > specify subdomains manually if you want. > > Jed > > On Sep 23, 2010 1:51 PM, "Leo van Kampenhout" <lvankampenhout at gmail.com> > wrote: > > Hi all, > > With p number of processors in the communicator, the block preconditioner > PC_BJACOBI will by default use p blocks. So far, so good. However, in order > to compare this algorithmic efficiency decrease (since the bigger p, the > less efficient the preconditioner), i ran the commands > > mpirun -n 1 ./program -pc_bjacobi_blocks 8 > mpirun -n 8 ./program -pc_bjacobi_blocks 8 > > I expected the preconditioning to be equally efficient in this case. > However, GMRES makes more iterations in the first case (30 against 28) which > I cannot explain. Are there more subtle differences about the preconditioner > or the KSP that i'm overlooking here? > > regards, > > Leo > > > > > > -------------- next part -------------- An HTML attachment was scrubbed... URL: <http://lists.mcs.anl.gov/pipermail/petsc-users/attachments/20100923/3ba0a665/attachment.htm>
