using MUMPS with mg

[Thomas Geenen]

On Monday 23 June 2008 16:08, Barry Smith wrote:
> On Jun 23, 2008, at 4:52 AM, Thomas Geenen wrote:
> > dear Petsc users,
> >
> > when using mg with Petsc (ml to be precise)
> > the default solver on the coarsest level is "redundant"
> > (I could not find much info in either the usermanual or de online
> > manuals about this solver)
> >
> > it seems to be a sequential LU factorization running on all cpu's at
> > the same time?
> > doing the same thing?
>
>     Correct.
>
> > i try to use MUMPS instead.
> > i try to invoke mumps by calling
> > ierr = PetscOptionsSetValue("-mg_coarse_ksp_type", "preonly");
> > ierr = PetscOptionsSetValue("-mg_coarse_mat_type", "aijmumps");
> > ierr = PetscOptionsSetValue("-mg_coarse_pc_type", "lu");
> >
> > this gives me
> >
> > [0]PETSC ERROR: --------------------- Error Message
> > ------------------------------------
> > [0]PETSC ERROR: No support for this operation for this object type!
> > [0]PETSC ERROR: Matrix type mpiaij  symbolic
> >
> > so apparently Petsc did not convert the matrix on the coarsest level.
> > if i remove the pc_type the conversion option is ignored and Petsc
> > uses redundant.
>
>    How are you generating the coarse grid matrix? Do you get it with
> DAGetMatrix()?

its handled in ml.c

from ml.c
  } else { /* convert ML P and R into shell format, ML A into mpiaij format */
    for (mllevel=1; mllevel<Nlevels; mllevel++){
      mlmat  = &(ml_object->Pmat[mllevel]);
      ierr = MatWrapML_SHELL(mlmat,reuse,&gridctx[level].P);CHKERRQ(ierr);
      mlmat  = &(ml_object->Rmat[mllevel-1]);
      ierr = MatWrapML_SHELL(mlmat,reuse,&gridctx[level].R);CHKERRQ(ierr);

      mlmat  = &(ml_object->Amat[mllevel]);
      if (reuse){
        ierr = MatDestroy(gridctx[level].A);CHKERRQ(ierr);
      }
      ierr = MatWrapML_MPIAIJ(mlmat,&gridctx[level].A);CHKERRQ(ierr);
      level--;
    }
  }

from  MatWrapML_MPIAIJ(

ierr = MatCreate(mlmat->comm->USR_comm,&A);CHKERRQ(ierr);
ierr = MatSetSizes(A,m,n,PETSC_DECIDE,PETSC_DECIDE);CHKERRQ(ierr);
ierr = MatSetType(A,MATMPIAIJ);CHKERRQ(ierr);


> Or MatCreateMPIAIJ()? Do you set the matrix prefix to -mg_coarse?
> It is not set automatically. You need to either call MatSetFromOptions()
> on the coarse matrix or directly call MatSetType() with aijmumps to set
> it the type.

i will check if just adding 

ierr = MatConvert(A, MATAIJMUMPS, MAT_REUSE_MATRIX,&A);CHKERRQ(ierr);

will do the trick

>
>     Barry
>
> > cheers
> > Thomas