[petsc-dev] MatMatMult gives different results

[Alexander Grayver]

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
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