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

[Vijay Gopal Chilkuri]

Hi,

I am using SLEPc to get the lowest m eigenvalues of a large sparse
hermitian matrix using Krylov-Schur.
The problem is that while asking for a large number of eigenvalues (e.g.
300) for a large problem
consisting of a 91454220 X 91454220 system, the solver does not give the
lowest 300 eigenvalues.
Instead it gives the following arbitrary negative values followed by a few
correct ones.

   -4733.882429           0.999888
>    -4729.554413             1.0006
>    -4725.841715           0.999887
>    -4702.457861            1.00061
>    -4700.608105           0.999887
>    -4691.142733           0.999885
>       -6.361168            1.18973
>       -6.361102        6.05898e-09
>       -6.361099           6.71e-09
>       -6.361093        7.66471e-09
>       -6.361082            1.17659



Although the solver says that it has successfully converged the 300
eigenvalues !
Please find the relevant files attached.

Could anyone tell me what I'm doing wrong ?

thanks,
 Vijay
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