On Thu, Mar 22, 2012 at 3:32 PM, Gao Bin <bin.gao at uit.no> wrote: > Hi, Jed > > Thank you very much for your quick reply. May I ask two more further > questions? > > (1) Why does not PETSc also partition the columns so that each processor > could use less memory? >
2D distributions are not efficient for sparse matrices. They are sometimes used for dense. > (2) If the matrix I use is a square matrix, the number of local columns > "n" should be equal to the number of local rows "m" when calling > MatCreateMPIDense, am I right? > Yes. You can always let PETSc choose by giving PETSC_DETERMINE. Matt > Thank you again for your answer. > > Cheers > > Gao > ------------------------------ > *From:* petsc-users-bounces at mcs.anl.gov [petsc-users-bounces at > mcs.anl.gov] > on behalf of Jed Brown [jedbrown at mcs.anl.gov] > *Sent:* Thursday, March 22, 2012 9:17 PM > *To:* PETSc users list > *Subject:* Re: [petsc-users] storage of parallel dense matrices and > (anti)symmetric matrices > > 2012/3/22 Gao Bin <bin.gao at uit.no> > >> "The parallel dense matrices are partitioned by rows across the >> processors, so that each local rectangular submatrix is stored in the dense >> format described above." >> >> Does it mean each processor will have several continuous rows and all >> columns of the matrix? If yes, why do we need to specify "n" -- the number >> of local columns when calling MatCreateMPIDense? >> > > Interpret the local column size n as the local size of the Vec that the > Mat will be applied to. > > >> I am sorry to raise this simple question, since I have read the manual >> and tutorials, but I have not found a clear answer. Moreover, the reason I >> am asking this question is that I would like to use PETSc for matrix >> operations, but the elements of matrices need to be calculate via my own >> code. If I know the distribution of the matrix, I could let each processor >> only calculate and set local values (the rows and columns possessed on the >> processor itself) for efficiency. >> >> My second question is if PETSc provides symmetric and anti-symmetric >> matrices. I have read the manual, the answer seems to be no. Am I right? > > > See the SBAIJ format (it is sparse). > > With a parallel dense matrix, there isn't any point using a symmetric > format unless you use a different distribution of the entries. > -- 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/20120322/a67d4350/attachment.htm>
