On Wed, Apr 25, 2012 at 02:21, Thomas Witkowski < thomas.witkowski at tu-dresden.de> wrote:
> Is it possible to create a parallel matrix (MPIAIJ) with empty size on > some ranks? Even if this should work, does it make sense (with respect to > runtime and efficiency) to collect all ranks having a nonempty contribution > the the global matrix in an mpi group and to use this communicator for > matrix create/computations? It depends how many ranks are empty. For coarse levels of multigrid (where this situation arises frequently), it's sometimes worthwhile to also move the data to a part of the machine that is topologically "close". Identifying "closeness" is not always easy because MPI does not necessarily expose this information in a useful fashion. What is the circumstance where this occurs for you? -------------- next part -------------- An HTML attachment was scrubbed... URL: <http://lists.mcs.anl.gov/pipermail/petsc-users/attachments/20120425/187cb266/attachment.htm>
