[petsc-users] Incorrect Eigenvalues when Setting KSP and PC types

[Greg Meyer]

Hi all,

Hong--looking at your link, there may be no special algorithm for Hermitian
matrices in MUMPS, but that doesn't mean it can't solve them like it would
any matrix. Furthermore it appears that Cholesky of complex matrices is
supported from this link:
https://www.mcs.anl.gov/petsc/documentation/linearsolvertable.html

So do you or anyone have any idea why I get incorrect eigenvalues?

Thanks,
Greg

On Thu, Sep 21, 2017 at 5:51 PM Greg Meyer <gregory.meyer at gmail.com> wrote:

> Ok, thanks. It seems that PETSc clearly should throw an error in this case
> instead of just giving incorrect answers? I am surprised that it does not
> throw an error...
>
> On Thu, Sep 21, 2017 at 5:24 PM Hong <hzhang at mcs.anl.gov> wrote:
>
>> Greg :
>>
>>> Yes, they are Hermitian.
>>>
>>
>> PETSc does not support  Cholesky factorization for Hermitian.
>> It seems mumps does not support Hermitian either
>>
>> https://lists.mcs.anl.gov/mailman/htdig/petsc-users/2015-November/027541.html
>>
>> Hong
>>
>>
>>> On Thu, Sep 21, 2017 at 3:43 PM Hong <hzhang at mcs.anl.gov> wrote:
>>>
>>>> Greg:
>>>>
>>>> OK, the difference is whether LU or Cholesky factorization is used. But
>>>>> I would hope that neither one should give incorrect eigenvalues, and when I
>>>>> run with the latter it does!
>>>>>
>>>> Are your matrices symmetric/Hermitian?
>>>> Hong
>>>>
>>>>>
>>>>> On Thu, Sep 21, 2017 at 2:05 PM Hong <hzhang at mcs.anl.gov> wrote:
>>>>>
>>>>>> Gregory :
>>>>>> Use '-eps_view' for both runs to check the algorithms being used.
>>>>>> Hong
>>>>>>
>>>>>> Hi all,
>>>>>>>
>>>>>>> I'm using shift-invert with EPS to solve for eigenvalues. I find
>>>>>>> that if I do only
>>>>>>>
>>>>>>> ...
>>>>>>>   ierr = EPSGetST(eps,&st);CHKERRQ(ierr);
>>>>>>>   ierr = STSetType(st,STSINVERT);CHKERRQ(ierr);
>>>>>>> ...
>>>>>>>
>>>>>>> in my code I get correct eigenvalues. But if I do
>>>>>>>
>>>>>>> ...
>>>>>>>   ierr = EPSGetST(eps,&st);CHKERRQ(ierr);
>>>>>>>   ierr = STSetType(st,STSINVERT);CHKERRQ(ierr);
>>>>>>>   ierr = STGetKSP(st,&ksp);CHKERRQ(ierr);
>>>>>>>   ierr = KSPGetPC(ksp,&pc);CHKERRQ(ierr);
>>>>>>>   ierr = KSPSetType(ksp,KSPPREONLY);CHKERRQ(ierr);
>>>>>>>   ierr = PCSetType(pc,PCCHOLESKY);CHKERRQ(ierr);
>>>>>>> ...
>>>>>>>
>>>>>>> the eigenvalues found by EPS are completely wrong! Somehow I thought
>>>>>>> I was supposed to do the latter, from the examples etc, but I guess that
>>>>>>> was not correct? I attach the full piece of test code and a test matrix.
>>>>>>>
>>>>>>> Best,
>>>>>>> Greg
>>>>>>>
>>>>>>
>>>>>>
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