[petsc-users] Restarting a SLEPC run to refine an eigenvector

[LUTSKO James]

I withdraw my question. In trying to put together an example to illustrate the problem, I found that EPSSetInitialSubspace() does indeed "work" - in the sense that the eigenvalue, which decreases monotonically during the calculation, picks up from where the previous run left off. I am not sure why I had previously thought it was otherwise.

thanks

% James F. Lutsko, CNLPCS, Universite Libre de Bruxelles,
% Campus Plaine -- CP231  B-1050 Bruxelles, Belgium
% tel: +32-2-650-5997   email: jlutsko at ulb.ac.be
% fax: +32-2-650-5767
________________________________
From: Jose E. Roman <jroman at dsic.upv.es>
Sent: Tuesday, March 28, 2023 7:43 PM
To: LUTSKO James <Jim.Lutsko at ulb.be>
Cc: petsc-users at mcs.anl.gov <petsc-users at mcs.anl.gov>
Subject: Re: [petsc-users] Restarting a SLEPC run to refine an eigenvector

What do you mean that EPSSetInitialSubspace() does not work? Doesn't it improve convergence with respect to not using it?

Is your smallest eigenvalue positive? And do you have many eigenvalues close to the smallest one?

Jose


> El 28 mar 2023, a las 17:32, LUTSKO James via petsc-users <petsc-users at mcs.anl.gov> escribió:
>
> Hello,
>  I am a complete newbe so sorry if this is answered elsewhere or ill-posed but .. I am trying to get the smallest eigenvector of a  large matrix. Since the calculations are very long, I would like to be able to restart my code if I find that the "converged" eigenvector is not good enough without having to start from scratch. I am currently using the options
>
> -eps_type jd  -eps_monitor -eps_smallest_real -eps_conv_abs -eps_tol 1e-8 -st_ksp_type gmres -st_pc_type jacobi -st_ksp_max_it 40
>
> Is there any way to do this? I have tried using EPSSetInitialSubspace with the stored eigenvector but this does not seem to work.
>
> thanks
> jim
>
> % James F. Lutsko, CNLPCS, Universite Libre de Bruxelles,
> % Campus Plaine -- CP231  B-1050 Bruxelles, Belgium
> % tel: +32-2-650-5997   email: jlutsko at ulb.ac.be
> % fax: +32-2-650-5767

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