On Sun, Jan 20, 2013 at 12:26 PM, Hui Zhang <mike.hui.zhang at hotmail.com>wrote:
> > On Jan 20, 2013, at 5:28 PM, Jed Brown wrote: > > > On Sun, Jan 20, 2013 at 10:22 AM, Hui Zhang <mike.hui.zhang at hotmail.com> > wrote: > > > > On Jan 20, 2013, at 5:13 PM, Jed Brown wrote: > > > > > No, MatMult and MatMatMult require all objects to be on the same > communicator. > > > > Thanks for the quick answer! It seems a general rule that all operands > and results must be > > on the same communicator. Can I lift an object from a sub-communicator > to the sup-communicator > > without changing the parallel layout of the object? > > > > You can with a Vec (e.g., using VecPlaceArray), but you're responsible > for the sharing so it's fragile. > > > > In general, I recommend creating the object on the largest communicator > involved and then getting access more locally. In the first pass, just make > a copy to a local subcomm unless a routine exists to do it automatically. > If you profile and see that the copy is significant (remarkably rare in > practice) you can sometimes optimize what is copied versus shared, or > change the parent parallel data structure to make the local access faster. > > I think about the method and find it is not as convenient as allowing > inter-communicator operations. > For example, VecScatter actually allows the two Vec in different > communicators (or one must include > the other?). > This is about the design of MPI. > I have more questions. > (1) Does MatScatter supports MatMatMult? > No > (2) Does MatConvert works on MATNEST? > Yes, for AIJ > (3) Does MatGetLocalSubMat support localization to a sub-communicator > instead of a process? > No, use MatGetSubMatrix. Matt > Thanks! > > > > > > > > > > > > On Sun, Jan 20, 2013 at 10:12 AM, Hui Zhang < > mike.hui.zhang at hotmail.com> wrote: > > > parallel Mat, multiplies a serial Vec or a serial Mat > > > > > > Is it supported directly? If yes, can the resulting Vec/Mat be serial > or parallel? > > > > > > > > > > > > -- 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/20130120/97b83618/attachment.html>
