Thanks for the answer. When I want to set a preconditioner then I will need to do that via STGetKSP and the KSPGetPC ? In the end I want to use a shell preconditioner. On Thu, Feb 16, 2012 at 7:54 AM, Jose E. Roman <[email protected]> wrote:

El 16/02/2012, a las 16:41, Verena Kuhlemann escribió:

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Hi,

I am trying to use LOBPCG via Slepc and I am a little confused on how to set the preconditioner and operator matrices. I have a shell matrix A and a matrix P that should be used for the preconditioning. Here is the relevant part of my code:

EPSCreate(PETSC_COMM_WORLD,&eps); EPSSetOperators(eps, A, PETSC_NULL); EPSSetProblemType(eps, EPS_HEP); EPSSetType(eps, EPSBLOPEX); EPSGetST(eps, &st); STPrecondSetMatForPC(st, P); STGetKSP(st,&ksp); KSPGetPC(ksp, &pc); KSPSetOperators(ksp,A, P, DIFFERENT_NONZERO_PATTERN); //do I have to set this?? If I don't the program complains that a matrix is not set PCSetType(pc, PCJACOBI); EPSSetUp(eps);

Is that correct or do I need to do something else?

Thanks, Verena

It works for me like this:

ierr = EPSCreate(PETSC_COMM_WORLD,&eps);CHKERRQ(ierr); ierr = EPSSetOperators(eps,A,PETSC_NULL);CHKERRQ(ierr); ierr = EPSSetProblemType(eps,EPS_HEP);CHKERRQ(ierr); ierr = EPSSetType(eps,EPSBLOPEX);CHKERRQ(ierr); ierr = EPSGetST(eps,&st);CHKERRQ(ierr); ierr = STPrecondSetMatForPC(st,P);CHKERRQ(ierr); ierr = EPSSetFromOptions(eps);CHKERRQ(ierr);

You don't need to manipulate the KSP or PC objects.

If you want to check whether your matrix P is being used in Blopex, you can do ierr = PetscObjectSetName((PetscObject)P,"My precond");CHKERRQ(ierr);

then run with -eps_view and you will see "Matrix Object: My precond 1 MPI processes" in the PC section.

Jose