[petsc-dev] MatMult

[Stefano Zampini]

Just an update: I ran with -info, and saw that the 186x6 matrix uses
compressed rows routines, whereas 171x21 does not.


2013/10/9 Stefano Zampini <s.zampini at cineca.it>

> I just noticed unexpected behaviour of MatMult_SeqBAIJ_3 in PCBDDC code
> (on branch stefano_zampini/pcbddc-baijfixes) with rectangular matrices
> having number of rows >> number of cols and number of cols =2*blocksize. I
> guess this problem will show up for other values of block sizes.
>
> When some rows of the matrix are empty, the corresponding entry in the
> resulting vector is not zero (as expected, mathematically speaking);
> instead, the values are not overwritten at all. Is it the expected
> behaviour?
>
> Attached are two matrices . The one with sizes 186x6 shows the problem on
> my laptop (ubuntu, gnu compilers,  --with-debugging, , CFLAGS -g -O0)
>
> I'm not familiar with PETSc low-level implementation of BAIJ, so I cannot
> dig anymore into the problem apart saying that:
>
> A) if "converted" to SeqAIJ with a call
>
> MatConvert(Mymat,MATSEQAIJ,MAT_REUSE_MATRIX,&Mymat)
>
> the output of MatMult is always correct.
>
> B) the problem disappear by increasing the number of columns (the matrix
> with sizes 171x21 does not show the problem).
>
>
> Hope you can reproduce the problem,
> --
>
> Ph. D. Stefano Zampini
>
>
> CINECA
> SuperComputing Applications and Innovations Department - SCAI
> Via dei Tizii, 6 00185 Roma - ITALY
> ------------------------------------------------------------------------------------------------------------------------
> Email: s.zampini at cineca.it
> SkypeID: stefano.zampini
> GoogleTalk: stefano.zampini at gmail.com
> Tel: +39 06.44486.707
> ------------------------------------------------------------------------------------------------------------------------
>
>


-- 

Ph. D. Stefano Zampini
CINECA
SuperComputing Applications and Innovations Department - SCAI
Via dei Tizii, 6 00185 Roma - ITALY
------------------------------------------------------------------------------------------------------------------------
Email: s.zampini at cineca.it
SkypeID: stefano.zampini
GoogleTalk: stefano.zampini at gmail.com
Tel: +39 06.44486.707
------------------------------------------------------------------------------------------------------------------------
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