[petsc-users] Setting values of a matrix in a blockwise manner

[Matthew Knepley]

On Wed, Jun 10, 2015 at 9:55 AM, Tim Steinhoff <kandanovian at gmail.com>
wrote:

> Thanks for the quick reply!
>
> "Yes, however in order to get improved performance, you need type MATBAIJ."
>
> I considered MatSetType(A,MATAIJ); i.e. the non-block type since
> UMFPACK seems to require the seqaij type according to the summary
> page. So do I have to refrain from using the more amiable block-type
> if I want to make use of UMFPACK?
>

Yes, I think so. What do you need in UMFPACK?

  Thanks,

    Matt


> 2015-06-10 16:45 GMT+02:00 Matthew Knepley <knepley at gmail.com>:
> > On Wed, Jun 10, 2015 at 9:42 AM, Tim Steinhoff <kandanovian at gmail.com>
> > wrote:
> >>
> >> Hi all
> >>
> >> I want to use Petsc to solve some linear systems via the built-in Krylov
> >> subspace methods as well as by means of UMFPACK.
> >>
> >> The considered matrix is block sparse with blocks of size 6x6.
> >>
> >> Here is what I came up with after taking a look at some of the examples
> >>
> >> MPI_Comm comm;
> >> Mat A;
> >> PetscInt n = 10000; /* dimension of matrix */
> >> comm = PETSC_COMM_SELF;
> >> MatCreate(comm,&A);
> >> MatSetSizes(Amat,n,n,n,n);
> >> MatSetBlockSize(A,6);
> >> MatSetType(A,MATAIJ); /* UMFPACK compatible format due to comm =
> >> PETSC_COMM_SELF */
> >>
> >> Questions:
> >> 1.
> >> I work on a single node with 2-8 cores. Hence, comm = PETSC_COMM_SELF; I
> >> guess. Is it correct in this contect to set MatSetSizes(Amat,n,n,n,n);
> with
> >> 4-times n?
> >
> >
> > Yes.
> >
> >>
> >> 2.
> >> After the above sequence of commands do I have to use something like
> >>   MatSeqAIJSetPreallocation(A,0,d_nnz); /* d_nnz <-> number of nonzeros
> >> per row */
> >> or is it possible to use
> >>   MatSeqBAIJSetPreallocation(A,6,0,db_nnz); /* db_nnz <-> number of
> block
> >> nonzeros per block row */
> >
> >
> > You should use this if using MATBAIJ.
> >
> >>
> >> In any case, is something like
> >>   MatSetValuesBlocked(A,1,idx_r,1,idx_c,myblockvals,INSERT_VALUES);
> >> to fill values of one block into the matrix A ok?
> >
> >
> > Yes, however in order to get improved performance, you need type MATBAIJ.
> >
> >   Thanks,
> >
> >     Matt
> >
> >>
> >> Regards
> >> Tim
> >
> >
> >
> >
> > --
> > What most experimenters take for granted before they begin their
> experiments
> > is infinitely more interesting than any results to which their
> experiments
> > lead.
> > -- Norbert Wiener
>



-- 
What most experimenters take for granted before they begin their
experiments is infinitely more interesting than any results to which their
experiments lead.
-- Norbert Wiener
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