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

[Hong]

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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