[petsc-users] Solving tridiagonal hermitian generalized eigenvalue problem with SLEPC

[Toon Weyens]

Yes, you are probably right: My code is not yet bug free (by all means!).
However, I have been working very hard on it and I will see if I find
something. B should not ever be really singular!

I do, however, still have some questions:

- Does slepc detect whether my matrix is tridiagonal and does it apply a
direct method to solve it? Or do you talk about it in general: that it
would be better for me to use a direct method that is not part of slepc?
- How do I make use of the information that both A and B have the same
non-zero structure? Is there an easy way?
- What is the call "MatSetOption(mat,MAT_HERMITIAN,PETSC_TRUE,ierr)" do? Is
it important? It does not seem to influence anything...

Thank you for your time and pacience!

Toon



On 19 August 2014 15:40, Jed Brown <jed at jedbrown.org> wrote:

> Toon Weyens <tweyens at fis.uc3m.es> writes:
>
> > Okay I reread again your answers and it seems that I missed the fact
> that I
> > do not need shift invert to find the EV with the largest real part?
>
> Correct, inversion is way more expensive and used to find internal
> eigenvalues.
>
> > Then the "trick" of ex. 13 does not apply (they look for something
> > close to 0).  So what could I do to avoid the LU?
>
> Is your matrix B singular?  What are its boundary conditions?  You have
> to solve with B for the generalized eigenvalue problem.  That could be
> done iteratively, but a direct solve makes sense for a tridiagonal
> system and the zero pivot likely indicates a deeper issue with the
> formulation that won't vanish simply by avoiding LU.
>
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