<div dir="ltr"><div dir="ltr">On Wed, Apr 14, 2021 at 5:56 PM Sam Guo <<a href="mailto:sam.guo@cd-adapco.com">sam.guo@cd-adapco.com</a>> wrote:<br></div><div class="gmail_quote"><blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left:1px solid rgb(204,204,204);padding-left:1ex"><div dir="ltr">Dear PETSc dev team,<div>   If I want PETSc to use my own parallel partition(instead of PETSc "evenly" partition rows), I assume I can provide local rows/columns as follows. </div><div><pre style="color:rgb(0,0,0)"><a href="https://www.mcs.anl.gov/petsc/petsc-current/docs/manualpages/Mat/MatCreateShell.html#MatCreateShell" target="_blank">MatCreateShell</a>(<a href="https://www.mcs.anl.gov/petsc/petsc-current/docs/manualpages/Sys/MPI_Comm.html#MPI_Comm" target="_blank">MPI_Comm</a> comm,<a href="https://www.mcs.anl.gov/petsc/petsc-current/docs/manualpages/Sys/PetscInt.html#PetscInt" target="_blank">PetscInt</a> m,<a href="https://www.mcs.anl.gov/petsc/petsc-current/docs/manualpages/Sys/PetscInt.html#PetscInt" target="_blank">PetscInt</a> n,<a href="https://www.mcs.anl.gov/petsc/petsc-current/docs/manualpages/Sys/PetscInt.html#PetscInt" target="_blank">PetscInt</a> M,<a href="https://www.mcs.anl.gov/petsc/petsc-current/docs/manualpages/Sys/PetscInt.html#PetscInt" target="_blank">PetscInt</a> N,void *ctx,<a href="https://www.mcs.anl.gov/petsc/petsc-current/docs/manualpages/Mat/Mat.html#Mat" target="_blank">Mat</a> *A)</pre></div><div>  If that's the case, what role does local columns play? Memory allocation? Should I use n (the global rows) or local rows or PETSC_DECIDE in this case?</div></div></blockquote><div><br></div><div>The only role played by n is to match this matrix with parallel vectors that you want it to act on. The local sizes should match. For square matrices, this usually</div><div>means you match the local row size.</div><div><br></div><div>  Thanks,</div><div><br></div><div>     Matt</div><div> </div><blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left:1px solid rgb(204,204,204);padding-left:1ex"><div dir="ltr"><div>Thanks,</div><div>Sam</div></div>
</blockquote></div><br clear="all"><div><br></div>-- <br><div dir="ltr" class="gmail_signature"><div dir="ltr"><div><div dir="ltr"><div><div dir="ltr"><div>What most experimenters take for granted before they begin their experiments is infinitely more interesting than any results to which their experiments lead.<br>-- Norbert Wiener</div><div><br></div><div><a href="http://www.cse.buffalo.edu/~knepley/" target="_blank">https://www.cse.buffalo.edu/~knepley/</a><br></div></div></div></div></div></div></div></div>