[petsc-users] Solve for all repeated eigenvalues

[Vinh Pham-Xuan]

You may try the contour integral method (CISS). Obviously, it is
computationally more expensive. I used the contour integral method on
MATLAB and it worked quite well. I expected the same result with SLEPc.

On Thu, 28 Jun 2018 at 23:22, Jose E. Roman <jroman at dsic.upv.es> wrote:

> This is a known issue of Krylov solvers. Sometimes you can workaround it
> by increasing the number of eigenvalues to compute (nev, for instance
> request twice as much as you need) and maybe reduce the mpd parameter to
> force more restarts. This approach is quite wasteful and still there is no
> guarantee that you get the full multiplicities right.
>
> To avoid the issue completely, use the lobpcg solver. However, SLEPc's
> implementation of lobpcg is not very well tuned, I have to take some time
> to improve it. You can also try the BLOPEX interface (configure
> --download-blopex in SLEPc).
>
> Jose
>
>
> > El 28 jun 2018, a las 22:53, Greg Meyer <gregory.meyer at gmail.com>
> escribió:
> >
> > Hi all,
> >
> > I'm using SLEPc to solve for some eigenvalues. If I ask for the
> eigenvalues with the leftmost real part (using SMALLEST_REAL), and there
> are repeated eigenvalues, it appears that the solver does not always find
> all of the repeated values before jumping up to the next unique eigenvalue.
> For example if the lowest eigenvalues of my matrix are [-12, -10, -10, -10,
> -8], and I request 4 eigenvalues, I may get [-12, -10, -10, -8]. I'm using
> the default solver. Is there any way, or any solver, that ensures that no
> eigenvalues are skipped?
> >
> > Thanks in advance,
> > Greg
>
>

-- 
Vinh Pham-Xuan, Ph.D
School of Electronic Engineering
Dublin City University
Ireland

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