Perhaps if you provide a brief summary of what you would like to do and we may have ideas on how to achieve it.
Barry Note: that MATNEST does require that all matrices live on all the MPI processes within the original communicator. That is if the original communicator has ranks 0,1, and 2 you cannot have a matrix inside MATNEST that only lives on ranks 1,2 but you could have it have 0 rows on rank zero so effectively it lives only on rank 1 and 2 (though its communicator is all three ranks). > On Mar 17, 2023, at 12:14 PM, Berger Clement <[email protected]> > wrote: > > It would be possible in the case I showed you but in mine that would actually > be quite complicated, isn't there any other workaround ? I precise that I am > not entitled to utilizing the MATNEST format, it's just that I think the > other ones wouldn't work. > > --- > Clément BERGER > ENS de Lyon > > > Le 2023-03-17 15:48, Barry Smith a écrit : > >> >> 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
