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[Scalapack] Process Grid Shape Trouble

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 

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 different 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 calculations:

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 a 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 

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
jason.sadowski@Domain.Removed <mailto:jason.sadowski@Domain.Removed>
Cell: 1-306-227-6066
/"He who never made a mistake never made a discovery"/ - Samuel Smiles
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