[petsc-users] Question about TSComputeRHSJacobianConstant

[Smith, Barry F.]

  There is no harm in having the GMRES there even if you use a direct solver (for testing) so just leave the GMRES. Changing to preonly every time you try LU is prone to error if you forget to change back.

   Barry


> On May 22, 2019, at 2:45 PM, Sajid Ali via petsc-users <petsc-users at mcs.anl.gov> wrote:
> 
> Hi Matt, 
> 
> Thanks for the explanation. That makes sense since I'd get reasonably close convergence with preonly sometimes and not at other times which was confusing.
> 
> Anyway, since there's no pc_tol (analogous to ksp_rtol/ksp_atol, etc), I'd have to more carefully set the gamg preconditioner options to ensure that it converges in one run, but since there's no guarantee that what works for one problem might not work for another (or the same problem at a different grid size), I'll stick with GMRES+gamg for now. 
> 
> Thank You, 
> Sajid Ali
> Applied Physics
> Northwestern University