[petsc-users] Basic question on making SNES continue its iterations

[sang pham van]

Hi Matt,

Is it true that the option -snes_linesearch_type basic will make SNES run
with the pure Newton method (without line search nor true region)?

Thank you.
Sang


On Wed, Jun 5, 2013 at 1:04 PM, Matthew Knepley <knepley at gmail.com> wrote:

> On Wed, Jun 5, 2013 at 12:33 PM, Gaurish Telang <gaurish108 at gmail.com>wrote:
>
>> I am trying to solve a non-linear system with PETSs's SNES solvers.
>>
>> To run my code, I am using the following options for snes set through the
>> command-line,
>> seen below.
>>
>> mpirun -np 1 ./Testvector \
>> -fBus      $1/Bus.mat \
>> -fYm       $1/Ym.mat \
>>  -ft       $1/t.mat \
>> -flinedata $1/linedata.mat \
>> -nox \
>> -snes_atol 1.e-5\
>> -snes_stol 1.e-6 \
>> -snes_rtol 1.e-12 \
>> -snes_max_it 100 \
>> -snes_max_linear_solve_fail 100  \
>> -snes_converged_reason \
>> -ksp_type preonly \
>> -pc_type lu \
>> -pc_factor_mat_solver_package superlu_dist \
>> -snes_monitor \
>> > result_superLU_dist.tmp 2>&1;
>>
>>
>> After feeding my data, I get the following output
>>  0 SNES Function norm 2.438306296478e+02
>>   1 SNES Function norm 1.679437793666e+02
>>   2 SNES Function norm 1.493618467597e+02
>>   3 SNES Function norm 4.622194635741e+01
>>   4 SNES Function norm 4.195017632984e+01
>> Nonlinear solve did not converge due to DIVERGED_LINE_SEARCH iterations 4
>>
>> As you can see the the SNES function norm is *decreasing*, which
>> indicates it is probably converging slowly to the actual solution. However
>> after just 4 iterations, it stops and indicates non-convergence, even
>> though my -snes_max_it = 100 as shown above.
>>
>> Is there a way to tell PETSc to continue its SNES iterations? Maybe some
>> there are some
>> default parameters which have to be changed?
>>
>
> You can try -snes_max_fail <num> or maybe -snes_linesearch_type basic.
>
>   Matt
>
>
>> Thank you
>>
>> Gaurish
>>
>
>
>
> --
> What most experimenters take for granted before they begin their
> experiments is infinitely more interesting than any results to which their
> experiments lead.
> -- Norbert Wiener
>
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.mcs.anl.gov/pipermail/petsc-users/attachments/20130910/a4aff331/attachment.html>