calculation time

[Jose E. Roman]

On 03/07/2009, Takuya Sekikawa wrote:

> Dear PETSc/SLEPc users,
>
> I have made eigenproblem solver program with SLEPc.
> Currently it works well, but it takes very long time to solve big
> problem.
>
> with 10000x10000 random matrix, it takes about 34 hours to solve.
> (solver = KrylovSchur, on 64bit Linux platform, 16G memory, 1 machine)
>
> Is this ordinally time to solve problem like these size?
> or Is there any good way to shorten calculation time?
>
> Thanks
> Takuya
> ---------------------------------------------------------------
>  Takuya Sekikawa
>         Mathematical Systems, Inc
>                    sekikawa at msi.co.jp
> ---------------------------------------------------------------

SLEPc is intended for computing part of the spectrum of a sparse  
matrix. If you want to compute a few eigenpairs of a 10000 matrix, it  
should be very fast. If you want to compute a large percentage of the  
spectrum (30% say) then you can do it with SLEPc but need to be more  
careful (use appropriate values of nev, ncv and mpd parameters).  
Finally, if you want to compute all eigenvalues, then you should not  
use SLEPc. The Lapack solver in SLEPc should be used only for  
debugging purposes in small problems. Please read the documentation.

Jose