[petsc-users] SLEPc generalized eigenvalue problem question?

[John Chludzinski]

Looks good but it only gives 4 eigenvalues.  How do I get the 50 smallest
eigenvalues?

---John

On Tue, Aug 2, 2011 at 3:40 AM, Jose E. Roman <jroman at dsic.upv.es> wrote:

>
> El 02/08/2011, a las 09:24, John Chludzinski escribió:
>
> > Jose,
> >
> > I used:
> >
> > MatCreateSeqAIJ(PETSC_COMM_SELF, n, n, 0, cnt, &A);
> > MatSetValue(A, i, j, *(a+i*SIZE+j), INSERT_VALUES);
> >
> > to create the input matrices.  Their sizes collapsed dramatically: from
> 192208072 to 239944. But again, using: ./ex7.exe -f1 k.dat -f2 m.dat
> -eps_gen_hermitian -eps_smallest_real > x.out 2>&1, I get:
> >
> > Generalized eigenproblem stored in file.
> >
> > Reading REAL matrices from binary files...
> > Number of iterations of the method: 500
> > Number of linear iterations of the method: 4009
> > Solution method: krylovschur
> >
> > Number of requested eigenvalues: 1
> > Stopping condition: tol=1e-07, maxit=500
> > Number of converged approximate eigenpairs: 0
> >
> > I'm really only interested in the least 50 eigenvalues.
> >
> > Smallest 10 eigenvalues
> > -0.000019
> > -0.000004
> > -0.000000
> > 0.000005
> > 0.000012
> > 0.000016
> > 2.795284
> > 2.795307
> > 21.235339
> > 21.235340
> > 81.582017
> >
> > Largest 10 eigenvalues
> > 176431487319.625000
> > 176431532012.467468
> > 176431562378.361359
> > 176435480628.136292
> > 176435488209.944031
> > 176435555689.747253
> > 176435563270.922424
> > 663312473823.916260
> > 663312473823.917969
> > 663312666285.928589
> > 663312666285.929810
> >
>
> You will never get convergence to the small eigenvalues in this way, since
> the largest ones are huge. Try something like:
> ./ex7.exe -f1 k.dat -f2 m.dat -eps_gen_hermitian -st_type sinvert
> -eps_target 1.0
>
> Jose
>
>
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.mcs.anl.gov/pipermail/petsc-users/attachments/20110802/09e746e8/attachment.htm>