[petsc-users] MatSetValues() for MATMPICUSP

[Jed Brown]

On Sat, Feb 11, 2012 at 00:00, recrusader <recrusader at gmail.com> wrote:

> in
> http://www.mcs.anl.gov/petsc/petsc-dev/src/ksp/ksp/examples/tutorials/ex43.c.html
>
> Why are two matrices set to MATAIJ? if I set MATAIJCUSP, is them changed?
>
> 1468: DMCreateMatrix<http://www.mcs.anl.gov/petsc/petsc-dev/docs/manualpages/DM/DMCreateMatrix.html#DMCreateMatrix>
> (da_Stokes,MATAIJ<http://www.mcs.anl.gov/petsc/petsc-dev/docs/manualpages/Mat/MATAIJ.html#MATAIJ>
> ,&A);
>
> 1469:   DMCreateMatrix <http://www.mcs.anl.gov/petsc/petsc-dev/docs/manualpages/DM/DMCreateMatrix.html#DMCreateMatrix>(da_Stokes,MATAIJ <http://www.mcs.anl.gov/petsc/petsc-dev/docs/manualpages/Mat/MATAIJ.html#MATAIJ>,&B);
>
>
You have to follow the code down to where those matrices are used.

1478:   AssembleA_Stokes(A,da_Stokes,da_prop,properties);
1479:   AssembleA_PCStokes(B,da_Stokes,da_prop,properties);

This uses a "block preconditioner", the B matrix is intentionally different
from the A matrix in order to handle the saddle point.
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