We need ISGlobalToLocalMappingApply(). This could be done with an STL map :)
Matt On Fri, Dec 23, 2011 at 1:01 AM, Jed Brown <jedbrown at mcs.anl.gov> wrote: > Can we enumerate the matrix operations that are known to be non-scalable > currently? > > 1. MatPermute() does ISAllGather() on the row indices and requires the > user to ISAllGather() the column indices before calling (I consider this to > be an interface bug similar to the MatGetSubMatrix() one we fixed before > petsc-3.1). The problem is that we have to determine the new row and column > or each locally visible row and column. This would be equivalent to having > a scalable ISInvertPermutation(), which is not difficult to implement, and > a way to retrieve data from off-process (new column indices for the "B" > part). The latter can be done with a "VecScatter for integers", or > trivially with PetscBG (name subject to change). > > 2. MatGetSubMatrix(), also called by MatPermute(). For this, it is > sufficient to determine where each currently owned entry should go (or be > skipped). We could do this by making a parallel int-vector for the entire > column space, setting it all to -1, then pushing the "new" column index > (location in the IS) over the IS. This gives a parallel vector that is -1 > for all column indices we don't want and the non-negative new column index > for those that we do want. Now we retrieve from the parallel vector > everything we need for the local column space. > > 3. MatIncreaseOverlap_MPISBAIJ(), I haven't looked carefully. > > I'm writing MatConvert_Nest_AIJ() which needs a similar feature. Mark > wants parallel MIS and MOOSE wants parallel coloring, both of which involve > moving integer data over the scatter context. > > What other implementations are currently non-scalable? Do we need other > primitives, or would two-way integer operations over the MPIXAIJ scatter > and via an IS be sufficient? > -- 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-dev/attachments/20111223/a738517f/attachment.html>
