[petsc-users] Solve for all repeated eigenvalues

[murat keçeli]

How about spectrum-slicing (i.e. -eps_interval -13,-7 -st_type sinvert
-st_ksp_type preonly -st_pc_type cholesky)? I guess you'd need real
symmetric matrices though.

On Thu, Jun 28, 2018 at 4:51 PM, Vinh Pham-Xuan
<vinh.phamxuan2 at mail.dcu.ie> wrote:
> 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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