[petsc-users] SLEPc Bogus eigenvalues for large -eps_nev

[Vijay Gopal Chilkuri]

Yes, those seem to be the right eigenvalues.
Ok so the solution is to recompile PETSc/SLEPc with a basic configuration
and test with --with-debugging=1

Would it make a difference if I use *-esp_type lanczos *or some other
diagonalization procedure ?

I'll run the test with a new version of PETSc/SLEPc and report back.

Thanks a  lot,
 Vijay

On Fri, May 15, 2015 at 2:55 PM, Jose E. Roman <jroman at dsic.upv.es> wrote:

>
> El 14/05/2015, a las 19:13, Vijay Gopal Chilkuri escribió:
>
> > oups sorry, I send you a smaller one (540540) this should finish in a
> few minutes.
> >
> > It requires the same makefile and irpf90.a library.
> > so just replace the old problem.c file with this and it should compile.
> >
> > Thanks again,
> >  Vijay
> >
>
> I was able to compute 300 eigenvalues of this matrix of size 540540. All
> eigenvalues are in the range -4.70811 .. -4.613807, and the associated
> residual is always below 1e-9.
>
> There must be something in your software configuration that is causing
> problems. I would suggest trying with a basic PETSc/SLEPc configuration,
> with no openmp flags, using --download-fblaslapack (instead of MKL). Also,
> although it should not make any difference, you may want to try with a
> smaller number of MPI processes (rather than 741).
>
> Jose
>
>
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