Current time (before start of timestep) 52.5048, iter=5380
Timestep=864.000000
0 SNES Function norm 1.650467412595e+05
0 KSP preconditioned resid norm 3.979123221160e+03 true resid norm
1.650467412595e+05 ||r(i)||/||b|| 1.000000000000e+00
1 KSP preconditioned resid norm 9.178246525982e-11 true resid norm
7.006473307032e-09 ||r(i)||/||b|| 4.245144892632e-14
Linear solve converged due to CONVERGED_RTOL iterations 1
1 SNES Function norm 6.722712947273e+02
Linear solve did not converge due to DIVERGED_NANORINF iterations 0
Nonlinear solve did not converge due to DIVERGED_LINEAR_SOLVE iterations 1
This usually is an indicator that the LU (ILU) factorization has hit a zero
pivot (hence the linear solve has a divide by zero so gives the
DIVERGED_NANORINF flag).
You can/should call SNESGetConvergedReason() immediately after each
SNESSolve(), if the result is negative that means something has failed in the
nonlinear solve and you can try cutting the time-step and trying again.
Good luck,
Barry
> On Aug 29, 2018, at 10:11 AM, Ling Zou <[email protected]> wrote:
>
> 1) My experience is that this kind of bug or sudden death (everything is fine
> till suddenly something is broken) is very difficult to debug/fix. I looked
> at your txt files and could not give any quick comments. Maybe PETSc
> developers have better idea on this.
> 2) I do have successful experience on reducing time step size when PETSc
> fails solving or my own piece of code throws an exception. If you are
> interested, I can share them.
>
> -Ling
> From: petsc-users <[email protected]> on behalf of Rahul Samala
> <[email protected]>
> Sent: Wednesday, August 29, 2018 8:36:58 AM
> To: PETSc Users List
> Subject: [petsc-users] Problem with SNES convergence
>
> Hello PetSc users,
>
> 1) I have problem with SNES convergence. I call SNESSolve in a time loop
> and use the inbuilt Jacobian feature. The code works fine for about 5380 time
> steps after which it breaks down. The solution till that point looks fine. I
> have used newtonls of type l2. (newtontr and others aren't working). Since I
> have used inbuilt Jacobian feature and the code worked for about 5000 time
> steps I don't understand the reason for failure, is it an incorrect function
> evaluation? Attached are the outputs with -pc_type lu and ilu along with
> -snes_linesearch_type l2 -snes_converged_reason -snes_monitor -snes_view
> -ksp_converged_reason -ksp_monitor_true_residual
>
> 2) How to get hold of failure signal, like Nonlinear solve DIVERGED_MAX_IT
> or DIVERGED_LINEAR_SOLVE so that whenever it occurs I can use a reduced time
> step and see if the code converges.
>
> Thank you,
> Rahul.
>
> output_ilu.txt
>
>
> output_ilu.txt
>
>
>
> output_lu.txt
>
>
> output_lu.txt
