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

[Matthew Knepley]

On Wed, Jun 10, 2015 at 10:31 AM, Tim Steinhoff <kandanovian at gmail.com>
wrote:

> One can switch on-the-fly?
>

Yes, either by changing the string in MatSetType() or calling
MatSetFromOptions() and passing

  -mat_type baij


> Say,
>
> we have a block sparse matrix A initilized via MatSetType(A,MATBAIJ)
> and subsequent calls of MatSeqBAIJSetPreallocation and
> MatSetValuesBlocked
>

The type determines the storage format, so you do not really want to change
after construction. YOu
can do this however using MatConvert().

  Thanks,

     Matt


> for use with e.g. the built-in Krylov subspace methods and afterwards
> changing type via MatSetType(A,MATAIJ)?
>
> Regards
> Tim
>
> 2015-06-10 17:24 GMT+02:00 Matthew Knepley <knepley at gmail.com>:
> > On Wed, Jun 10, 2015 at 10:20 AM, Tim Steinhoff <kandanovian at gmail.com>
> > wrote:
> >>
> >> I wanted to give the multi frontal LU factorization approach a shot as
> >> an example for a direct sparse solver.
> >
> >
> > You can just switch types when you use something other than UMFPACK.
> >
> >   Thanks,
> >
> >     Matt
> >
> >>
> >> Regards
> >> Tim
> >>
> >> 2015-06-10 17:00 GMT+02:00 Matthew Knepley <knepley at gmail.com>:
> >> > 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
> >
> >
> >
> >
> > --
> > 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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