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

[Gregory Meyer]

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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