performance question

[bruce]

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

[hongbo]

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.

[Julien Langou]

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

[bruce]

Hi, Julien:

Thank you for your advice!

Bruce