[petsc-users] Non-linear solve: DIVERGED_LINE_SEARCH

[Stefano Zampini]

The solver did not diverge.
It was the line search that was not able to make further progress in
minimizing the 2-norm of the residual.
This is common in nonlinear solvers. It would help if you tell us what you
are trying to solve.
Note that at the first step, your residual norm is already 1.e-6. What kind
of accuracy do you want?


Il giorno gio 7 set 2023 alle ore 13:08 Karthikeyan Chockalingam - STFC
UKRI via petsc-users <petsc-users at mcs.anl.gov> ha scritto:

> Hello,
>
>
>
> The non-linear solution diverged. The final solution seems right and I
> believe the Jacobian is correct (not 100% certain).
>
>
>
> I am not sure if I doing something wrong in the solver setting.
>
>
>
>
>
>  0 SNES Function norm 3.890991210938e-03
>
>     0 KSP Residual norm 9.037762538598e+00
>
>     1 KSP Residual norm 2.120375403775e-01
>
>     2 KSP Residual norm 5.155439334511e-03
>
>     3 KSP Residual norm 1.394364169369e-04
>
>     4 KSP Residual norm 9.233543407204e-06
>
>   Linear solve converged due to CONVERGED_RTOL iterations 4
>
>
>
>       Line search: Using full step: fnorm 3.890991210938e-03 gnorm
> 7.701511565083e-06
>
>   1 SNES Function norm 7.701511565083e-06
>
>     0 KSP Residual norm 5.630229687829e-03
>
>     1 KSP Residual norm 1.030475601271e-04
>
>     2 KSP Residual norm 2.576454714319e-06
>
>     3 KSP Residual norm 6.669316846898e-08
>
>     4 KSP Residual norm 3.215810984829e-09
>
>   Linear solve converged due to CONVERGED_RTOL iterations 4
>
>
>
>       Line search: gnorm after quadratic fit 1.805500533481e-05
>
>       Line search: Cubic step no good, shrinking lambda, current gnorm
> 2.563759884284e-05 lambda=3.0804668685096816e-02
>
>       Line search: Cubic step no good, shrinking lambda, current gnorm
> 3.332721829751e-05 lambda=3.0804668685096817e-03
>
>       Line search: Cubic step no good, shrinking lambda, current gnorm
> 4.102754045833e-05 lambda=3.0804668685096822e-04
>
>       Line search: Cubic step no good, shrinking lambda, current gnorm
> 4.872893294880e-05 lambda=3.0804668685096822e-05
>
>       Line search: Cubic step no good, shrinking lambda, current gnorm
> 5.643043250787e-05 lambda=3.0804668685096822e-06
>
>       Line search: Cubic step no good, shrinking lambda, current gnorm
> 6.413194279696e-05 lambda=3.0804668685096827e-07
>
>       Line search: Cubic step no good, shrinking lambda, current gnorm
> 7.183345417492e-05 lambda=3.0804668685096828e-08
>
>       Line search: Cubic step no good, shrinking lambda, current gnorm
> 7.953496567312e-05 lambda=3.0804668685096829e-09
>
>       Line search: Cubic step no good, shrinking lambda, current gnorm
> 8.723647719173e-05 lambda=3.0804668685096831e-10
>
>       Line search: Cubic step no good, shrinking lambda, current gnorm
> 9.493798871875e-05 lambda=3.0804668685096832e-11
>
>       Line search: Cubic step no good, shrinking lambda, current gnorm
> 1.026395002516e-04 lambda=3.0804668685096835e-12
>
>       Line search: Cubic step no good, shrinking lambda, current gnorm
> 1.103410117889e-04 lambda=3.0804668685096835e-13
>
>       Line search: unable to find good step length! After 12 tries
>
>       Line search: fnorm=7.7015115650831560e-06,
> gnorm=1.1034101178892401e-04, ynorm=6.2052357872955976e-03,
> minlambda=9.9999999999999998e-13, lambda=3.0804668685096835e-13, initial
> slope=-5.9313318983096354e-11
>
> Nonlinear solve did not converge due to DIVERGED_LINE_SEARCH iterations 1
>
>
>
>
>
> Thank you for your help.
>
>
>
> Kind regards,
>
> Karthik.
>
>
>
> --
>
> *Dr. Karthik Chockalingam*
>
> Senior Research Software Engineer
>
> High Performance Systems Engineering Group
>
> Hartree Centre | Science and Technology Facilities Council
>
> karthikeyan.chockalingam at stfc.ac.uk
>
>
>
>  [image: signature_3970890138]
>
>
>


-- 
Stefano
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