performance question

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performance question

Postby bruce » Mon Apr 09, 2007 9:50 pm

Hi, There:

I got two questions and hope you can help me. I am using PDSYEVX routine

1). What is the suggested block size in order to calculate the eigenvalue
and eigenvector for a symmetric matrix of size 20k X 20k, also what about 40k X 40k?

2). Given an eight-node cluster, can I set the prow and pcol to be 4 and 2
respectively for the aforementioned calculation?

Your help is higly appreciated!

Bruce
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Postby hongbo » Tue Apr 10, 2007 3:26 am

Based on ScaLapack User's Guide, which is BTW 10 years old, block size should be at least 64x64. For processor matrix, 4x2 is better than 8x1.

Just my 2 cents. I think real performance depends on your specific machine also. Better way is just to experiment.
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Postby Julien Langou » Tue Apr 10, 2007 11:50 am

The SEP problem (Symmetric Eigenvalue Problem) is not that much sensitive to the grid size. So basically take a grid as square as you can and you shoudl be good.
64x64 is a good idea. 80x80 when using ATLAS BLAS. Well, you need to try to know.
But think also to change of algorithms, if you want a few of the eigenvectors then PDSYEVX
is a good bet, but if you want them all, what about trying PDSYEVD.
Julien
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Thanks Julien

Postby bruce » Tue Apr 10, 2007 12:04 pm

Hi, Julien:

Thank you for your advice!

Bruce
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