[petsc-users] SNES convergence issue

[Jed Brown]

On Mon, May 16, 2011 at 14:27, Tian(ICT) <rongtian at ncic.ac.cn> wrote:

>  0 KSP preconditioned resid norm 1.393538348796e-001 true resid norm
> 7.81673715
> 5471e-001 ||Ae||/||Ax|| 1.000000000000e+000
>   1 KSP preconditioned resid norm 8.503891307640e-002 true resid norm
> 9.78452660
> 6728e-001 ||Ae||/||Ax|| 1.251740516806e+000
>   2 KSP preconditioned resid norm 2.769264336444e-005 true resid norm
> 3.06983248
> 7178e+001 ||Ae||/||Ax|| 3.927255613334e+001
>   3 KSP preconditioned resid norm 2.140259007162e-005 true resid norm
> 3.58014377
> 1001e+001 ||Ae||/||Ax|| 4.580099982632e+001
>   4 KSP preconditioned resid norm 3.271042954922e-006 true resid norm
> 3.39507468
> 5413e+000 ||Ae||/||Ax|| 4.343339961273e+000
>   5 KSP preconditioned resid norm 8.052808588169e-009 true resid norm
> 5.12770240
> 1411e-002 ||Ae||/||Ax|| 6.559901272645e-002
>  29 SNES Function norm 7.688867566940e-001


The linear systems are not being solved well. Try

./pgfem -snes_monitor -snes_mf_operator -mat_mffd_type ds -ksp_type fgmres
-ksp_monitor_true_residual -ksp_gmres_modifiedgramschmidt -ksp_rtol 1e-10
-pc_type lu

Remove the -pc_type lu if you have a known null space or otherwise expect
the system to be singular.
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