ScaLAPACK Archives

[Scalapack] Process Grid Shape Trouble

This is indeed baffling (as you put it). There is not much reason for a 
ScaLAPACK code to perform correctly on a given machine and to perform 
incorrectly on another one. Moreover if you managed to get the incorrect 
installation to correctly work from time to time. A suggestion is to try a 
different MPI ... I am not at all convinced that this will change the 
problem but I have no other suggestion.

On Tue, 6 Oct 2009, Jason Sadowski wrote:

Hello All,

I am currently using ScaLapack to perform research at the University of 
Saskatchewan and have encountered some peculiar problems.? I am using the 
PDSYEVD routine to
perform the diagonalization of a matrix however occasionally I get the wrong 
results.? I believe the problem may be a memory issue, but I am unable to 
determine what
is causing it.? I am hoping somebody can give me an idea as to where this 
problem may be occurring.

The matrix I am trying to diagonalize is 3200x3200 and I am using a block 
size of 32x32.? I've noticed that the eigenvalues returned by PDSYEVD are 
depending on the particular shape of the process grid I choose.? Inside my 
program I have the lines which perform:

PRINT Matrix A
Diagonalize ( A, Z)
PRINT Matrix(Z)

Where A is the input matrix, and Z is the matrix of eigenvectors returned 
from PDSYEVD.? I want to perform this calculation using 4 processors, so I 
can choose
process grids of 1x4, 2x2, or 4x1.? Here are the results of performing such 

1) Matrix A is independent of the grid shape.? It is the same in all cases.
2) Matrix Z is INCORRECT for grid shapes of 2x2 and 1x4.
3) Process grid 4x1 gives the CORRECT values for MatrixZ.

As I have mentioned before, I believe this may be some kind of memory issue.? 
The reason I think this is because I can perform the previous calculations on 
different machine (called vortex) with no errors.? Identical code ran on 
Vortex gives correct values of MatrixZ for all grid shapes.? Only on this 
specific machine
(iglu) do the process grid problems arise.? To my knowledge the only 
difference between the machines is that Vortex is a quad core machine with 8 
GB of RAM, while
iglu is a dual core machine ( with hyperthreading enabled ) and 4 GB of RAM.?

First I should ask are there any known issues with ScaLapack's memory 
distribution scheme and hyperthreading technology?? I realize this email is 
quite lengthy, but I
am completely baffled as to why this problem is occurring.? Any ideas or 
comments as to where I should be looking would be greatly appreciated.


Jason Sadowski
Jason Sadowski
Cell: 1-306-227-6066
"He who never made a mistake never made a discovery" - Samuel Smiles

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