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

[Tim Steinhoff]

I wanted to give the multi frontal LU factorization approach a shot as
an example for a direct sparse solver.

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