Question on MatPtAP

[Tobias Neckel]

Hello,

when moving from PETSc 2.3.2-p10 to 2.3.3-p13, I recently encountered a 
strange behaviour (segmentation fault) of the new version concerning the 
usage of MatPtAP. I tried to pull everything down to a simple test case. 
For square matrices (A as well as P), everything seems to work fine.

But when I set up a simple non-square example (A being the 3x3-identity, 
P being a 3x5 matrix, see attached file PETScLibTest.cpp), I encounter 
severe problems: As soon as P gets entries outside its 3x3 block (an 
entry P(0,3), e.g.), PETSc is telling me about Memory corruption while 
using MatPtAP (see part of command line output in the attached file 
output.txt, run with -info).

I used valgrind to check if sth. weird happens, but it is giving nothing 
until the PETSc error message.

Using the same test case with PETSc 2.3.2-p10 (with identic configuring 
options on the same machine) does not show any problems at all.

So I am a bit confused. Is it not allowed any longer to use MatPtAP with 
non-square matrices? I checked the online documentation but did not find 
anything ...

Next idea was to use MatMatMult directly to see if that works. So I used
MatMatMultTranspose(P, A, MAT_INITIAL_MATRIX, 1.0, &C1) and then
MatMatMult(C1, P, MAT_INITIAL_MATRIX, 1.0, &C)
to get C=C1*P=P^T*A*P in two steps. This time, everything works fine for 
the small test case from above, also with the new version 2.3.3-p13.


Best regards
Tobias Neckel

-- 
Dipl.-Tech. Math. Tobias Neckel

Institut für Informatik V, TU München
Boltzmannstr. 3, 85748 Garching

Tel.:   089/289-18602
Email:  neckel at in.tum.de
URL:    http://www5.in.tum.de/persons/neckel.html
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