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@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
