[petsc-dev] MatMatMult gives different results

[Alexander Grayver]

Hong,

On 07.02.2012 17:06, Hong Zhang wrote:
> Alexander:
> Thanks for sending matrix data and testing code.
> Before testing it, I have question about your code:
>
>
>       MatCreateMPIAIJ(PETSC_COMM_WORLD, PETSC_DECIDE, PETSC_DECIDE, N,
>     M, 12, PETSC_NULL, 12, PETSC_NULL, &AT);
>
>       MatTranspose(A,MAT_IGNORE_MATRIX,&AT);
>
>
> should be replaced with
> MatTranspose(A,MAT_INITIAL_MATRIX,&AT);

Hm, it seems this was the reason...

>
>     To compare results I use following Matlab script:
>
>     Cm = A.'*B;
>
>               ^
>
> Do you mean 'Cm = A'*B;'?
> 'Cm = A.'*B;' gives component-wise matrix product, not matrix product.

.' operator means non-Hermitian transpose. That is what I get with 
MatTranspose (in contrast with MatHermitianTranspose)
component-wise matrix product would be .*

>
> Hong
>
>     C = PetscBinaryRead('C.dat','complex',true);
>
>     Matrix C is different depending on number of cores I use.
>     My PETSc is:
>     Using Petsc Development HG revision:
>     876c894d95f4fa6561d0a91310ca914592527960  HG Date: Tue Jan 10
>     19:27:14 2012 +0100
>
>
>     On 06.02.2012 17:13, Hong Zhang wrote:
>>     MatMatMult() in petsc is not well-tested for complex - could be
>>     buggy.
>>     Can you send us the matrices A and B in petsc binary format for
>>     investigation?
>>
>>     Hong
>>
>>     On Mon, Feb 6, 2012 at 5:55 AM, Alexander Grayver
>>     <agrayver at gfz-potsdam.de <mailto:agrayver at gfz-potsdam.de>> wrote:
>>
>>         Dear PETSc team,
>>
>>         I try to use:
>>         call
>>         MatMatMult(A,B,MAT_INITIAL_MATRIX,PETSC_DEFAULT_DOUBLE_PRECISION,C,ierr);CHKERRQ(ierr)
>>
>>         Where both A and B are rectangular, but A is sparse and B is
>>         dense. Both are double complex and distributed.
>>         The product PETSc gives me contains some errors in some part
>>         of the matrix.
>>         I output A, B and C then computed product in matlab.
>>
>>         Attached you see figure plotted as:
>>         imagesc(log10(abs(C-Cm)))
>>
>>         Where Cm -- product computed in matlab.
>>
>>         The pattern and amplitude vary depending on the number of
>>         cores I use. This picture is obtained for 48 cores (I've
>>         tried 12, 64 cores as well).
>>
>>         Where should I look for possible explanation?
>>
>>         -- 
>>         Regards,
>>         Alexander
>>
>>
>
>
>     -- 
>     Regards,
>     Alexander
>
>


-- 
Regards,
Alexander

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