[petsc-users] eigensolution error with slepc

[Manav Bhatia]

Thanks! 
I upgraded to 3.6.3 and ran the code, and it went through all the load steps without problem. 

A followup question: 

It seems like the eigenvalues are sorted based on abs(lambda). If I am interested in only the lowest N eigenvalues greater than 0, is there a way to tell slepc to ignore all eigenvalues less than 0?  

Thanks,
Manav


> On Apr 4, 2016, at 11:30 AM, Jose E. Roman <jroman at dsic.upv.es> wrote:
> 
> 
>> El 4 abr 2016, a las 18:23, Manav Bhatia <bhatiamanav at gmail.com> escribió:
>> 
>> Thanks, Jose!
>> 
>> I am currently running 3.6.2, and will update to 3.6.3. 
>> 
>> Is there a recommended strategy to automatically switch from GHEP to GNHEP for some subset of problems? Or should I choose to run all my eigenprobelms with GNHEP? 
>> 
>> Regards,
>> Manav
> 
> Well you could consider doing a trick like this:
> 
>    PetscPushErrorHandler(PetscIgnoreErrorHandler,NULL);
>    ierr = EPSSolve(eps);
>    PetscPopErrorHandler();
>    if (ierr) {
>       ierr = EPSSetProblemType(eps,EPS_GNHEP);CHKERRQ(ierr);
>       ierr = EPSSolve(eps);CHKERRQ(ierr);
>    }
> 
> But this is very ugly and does not discriminate one particular error from others. A (costly) alternative would be to compute a rough approximation of the leftmost eigenvalue of your K matrix to see if it is negative.
> 
> Jose
>