[petsc-users] Slepc doesn't converge for some EV problems

[Sonya Blade]

Thank you very much.

Regards,


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> Subject: Re: [petsc-users] Slepc doesn't converge for some EV problems
> From: jroman at dsic.upv.es
> Date: Wed, 5 Jun 2013 08:33:31 +0200
> CC: petsc-users at mcs.anl.gov
> To: sonyablade2010 at hotmail.com
>
>
> El 05/06/2013, a las 07:52, Sonya Blade escribió:
>
>> Dear All,
>>
>> Sometimes I experience that Slepc is not converging for the requested
>> eigenvalues and simply resturns 0. I do take into consideration of setting
>> the requested eigenvalues from command line options rather then setting them
>> manually at the body of program.
>>
>> I observe this when I'm trying to solve this moderately large matrices e.g. 192x192
>> for small ones e.g. 48x48 there is not problem other than Slepc deviates from
>> requested to found EVs. For example if I request 7 eigenvalues to be found Slepc finds
>> 9 or 10, what could be the problem of this malfunctioning?
>>
>> Your help will be appreciated,
>>
>> Regards,
>
> 192 is very small. SLEPc is intended for large sizes (10,000 or more). For such small matrices, you would rather use LAPACK.
>
> It is normal that the solver returns more eigenvalues than requested. This is not a malfunctioning.
>
> If you get zero converged eigenvalues, try changing the parameters (e.g. ncv) or using a different strategy (e.g. shift-and-invert with a reasonable target).
>
> Jose
>