[petsc-users] SNES convergence tol question

[Mark F. Adams]

We've been trying to drive the nonlinear residual down and SNES seems to return  prematurely.

Appended is Dan's note.  We are asking for -snes_rtol 1.e-12 but only getting ~1.e-8.

Anyone have any ideas?

Mark

> Nonlinear solve converged due to CONVERGED_PNORM_RELATIVE iterations 8

However, here are the initial and final norms:

>   0 SNES Function norm 1.999411334131e+08
>   8 SNES Function norm 5.999267565004e-01

2e8/6e-1 = 3.3e8. So, I'm confused. Am I misunderstanding the convergence criterion?

here's the dump of petsc options at the end:

> #PETSc Option Table entries:
> -ksp_converged_use_initial_residual_norm
> -ksp_max_it 100
> -ksp_monitor
> -ksp_rtol 1.e-6
> -ksp_type gmres
> -mg_levels_ksp_max_it 4
> -options_left
> -pc_gamg_agg_nsmooths 1
> -pc_gamg_sym_graph
> -pc_gamg_threshold .01
> -pc_gamg_type agg
> -pc_gamg_verbose 2
> -pc_hypre_boomeramg_agg_nl 1
> -pc_hypre_boomeramg_coarsen_type HMIS
> -pc_hypre_boomeramg_interp_type ext+i
> -pc_hypre_boomeramg_no CF
> -pc_hypre_type boomeramg
> -pc_type gamg
> -snes_converged_reason
> -snes_mf_operator
> -snes_monitor
> -snes_rtol 1.e-12
> #End of PETSc Option Table entries



Mark