If you are using a MPIAIJ matrix that has already been created you can use MatMPIAIJGetSeqAIJ(). This gives you back on each process the "diagonal" block and the "off-diagonal" block.
> On Jun 17, 2019, at 7:44 AM, Eda Oktay via petsc-users > <[email protected]> wrote: > > Hello everyone, > > I am trying to find the off diagonal blocks of a matrix. For example, I > partitioned a 10*10 matrix into 4*4 and 6*6 block sub matrices. I need to > find the other blocks in order to find the number of nonzero elements in them. > > I tried to use MatGetLocalSubMatrix but I couldn't figure out how to give > iscol and isrow. Also, from the manual, ı understood that > MatSetLocalToGlobalMapping should be used before this routine but I couldn't > used it properly because before MatGetLocalSuMatrix, the submatrix doesn't > exist. I tried to give zero to all elements so that I can use Mapping > routine, but I got an error saying that it is invalid. > > How can I fix this probelm? > > Thank you, > > Eda
