[petsc-dev] MatMatMult gives different results

Tue Feb 7 13:18:12 CST 2012

Hong,

Thanks for explanation. I will try this tomorrow. Good to have this stuff in the help now.

And sorry for misleading you initially.

Regards,
Alexander

----- Reply message -----
From: "Hong Zhang" <hzhang at mcs.anl.gov>
To: "For users of the development version of PETSc" <petsc-dev at mcs.anl.gov>
Subject: [petsc-dev] MatMatMult gives different results
Date: Tue, Feb 7, 2012 19:09
Alexander :

There is something I didn't get yet, I hope you could clarify it. 

So, when I use flag MAT_INITIAL_MATRIX in test program it works
fine.
Good to know :-) 
If I put this flag in my original program I get dozens of exceptions
like:

[42]PETSC ERROR: Argument out of range!

[42]PETSC ERROR: New nonzero at (1336,153341) caused a malloc!
You cannot do  MatCreateMPIAIJ()
MatTranspose(A,MAT_INITIAL_MATRIX,&AT);

MatCreateMPIAIJ() creates AT and preallocates approximate nonzeros, which does not match exactly the nonzeros in 
MatTranspose(A,MAT_INITIAL_MATRIX,&AT);MatTranspose(A,MAT_INITIAL_MATRIX,&AT) creates matrix AT and sets correct nonzero pattern and values in AT. 
MatTranspose() only takes in "MAT_INITIAL_MATRIX" - for a new AT,
and "MAT_REUSE_MATRIX" when AT is created with MatTranspose(A,MAT_INITIAL_MATRIX,&AT)
and reuse for updating its values (not nonzero patten).

I'm updating petsc help menu on MatTranspose(). Thanks for the report.

Hong

I changed this flag to MAT_REUSE_MATRIX and exceptions disappeared,
but result is incorrect again (same as for MAT_IGNORE_MATRIX)  

I tried test program with MAT_REUSE_MATRIX and it also gives
different matrix product.

Since there is no description of MatReuse structure for MatTranspose
it's a bit confusing what to expect from it. 

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 .*

You are correct.

Hong 

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>
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

-- 
Regards,
Alexander
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