[petsc-users] CG+GAMG convergence issues in GHEP Krylov-Schur for some MPI runs

[Denis Davydov]

Hi Hong,

> On 6 Nov 2015, at 16:09, Hong <hzhang at mcs.anl.gov> wrote:
> 
> Denis:
> Do you use shift-and-invert method for solving eigenvalue problem?
no, it’s just shift with zero value. So for GHEP one inverts B-matrix.

> If so, the linear problems would be extremely ill-conditioned, for which the direct solver, such LU or Cholesky are usually the only working option.
Depends on the shift, i would say. 
In any case the same problem works with jacobi preconditioner no no other changes, 
so i would not relate it to any settings on SLEPc part.

> You may run your petsc/slepc code with option '-ksp_monitor' to observe convergence behavior.
Will do, thanks.

Regards,
Denis.