You may be able to mimic what you want by not using PETSC_DECIDE but instead computing up front how many rows of each matrix you want stored on each MPI process. You can use 0 for on certain MPI processes for certain matrices if you don't want any rows of that particular matrix stored on that particular MPI process.
Barry > On Mar 17, 2023, at 10:10 AM, Berger Clement <[email protected]> > wrote: > > Dear all, > > I want to construct a matrix by blocs, each block having different sizes and > partially stored by multiple processors. If I am not mistaken, the right way > to do so is by using the MATNEST type. However, the following code > > Call > MatCreateConstantDiagonal(PETSC_COMM_WORLD,PETSC_DECIDE,PETSC_DECIDE,4,4,2.0E0_wp,A,ierr) > Call > MatCreateConstantDiagonal(PETSC_COMM_WORLD,PETSC_DECIDE,PETSC_DECIDE,4,4,1.0E0_wp,B,ierr) > Call > MatCreateNest(PETSC_COMM_WORLD,2,PETSC_NULL_INTEGER,2,PETSC_NULL_INTEGER,(/A,PETSC_NULL_MAT,PETSC_NULL_MAT,B/),C,ierr) > > does not generate the same matrix depending on the number of processors. It > seems that it starts by everything owned by the first proc for A and B, then > goes on to the second proc and so on (I hope I am being clear). > > Is it possible to change that ? > > Note that I am coding in fortran if that has ay consequence. > > Thank you, > > Sincerely, > > -- > Clément BERGER > ENS de Lyon
