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

[Hong]

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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