[petsc-users] Snes behavior

[Ryan Yan]

Hi Barry,
Please see reply below,

On Sun, Jan 10, 2010 at 4:57 PM, Barry Smith <bsmith at mcs.anl.gov> wrote:

>
> On Jan 10, 2010, at 3:52 PM, Ryan Yan wrote:
>
>  Hi Barry,
>> Yes, exactly. The original multi-components system scale quite unevenly. I
>> will try to rescale it.
>> Could this be helpful to show some promise on quadratic convergence?
>>
>
>   I won't be concerned about "quadratic convergence" I'd only be concerned
> that it is converging to the correct answer and that you are getting close
> enough to the correct answer.
>
> Yes, I agree.


>    You can run with -snes_mf_operator and -snes_type test to verify if the
> Jacobian being computed is accurate. Perhaps in your function evaluation you
> are not using the stencil that you set with the DA, this would cause the
> wrong Jacobian to be computed.
>
>
After passing in -snes_mf_operator and -snes_type test as follows:
vyan2000 at vyan2000-linux ~/NCproject/general : mpirun -np 2 ./HeatProfile1D
-snes_mf_operator -snes_type test
I got errors, as expected:

[0]PETSC ERROR: --------------------- Error Message
------------------------------------
[0]PETSC ERROR: Invalid argument!
[0]PETSC ERROR: Cannot test with alternative preconditioner!
[0]PETSC ERROR:
------------------------------------------------------------------------
[0]PETSC ERROR: Petsc Release Version 3.0.0, Patch 5, Mon Apr 13 09:15:37
CDT 2009
[0]PETSC ERROR: See docs/changes/index.html for recent updates.
[0]PETSC ERROR: See docs/faq.html for hints about trouble shooting.
[0]PETSC ERROR: See docs/index.html for manual pages.
[0]PETSC ERROR:
------------------------------------------------------------------------
[0]PETSC ERROR: ./HeatProfile1D on a O-hypre-p named vyan2000-linux by
vyan2000 Sun Jan 10 17:16:00 2010
[0]PETSC ERROR: Libraries linked from
/home/vyan2000/local/PPETSc/petsc-3.0.0-p5/O-hypre-prometheus/lib
[0]PETSC ERROR: Configure run at Thu Jun 25 13:49:36 2009
[0]PETSC ERROR: Configure options --download-mpich=1 --with-debugger=gdb
--download-hypre=1 --download-parmetis=1 --download-prometheus=1
--with-shared=0
[0]PETSC ERROR:
------------------------------------------------------------------------
[0]PETSC ERROR: SNESSolve_Test() line 28 in src/snes/impls/test/snestest.c
[0]PETSC ERROR: SNESSolve() line 2221 in src/snes/interface/snes.c
[0]PETSC ERROR: DMMGSolveSNES() line 510 in src/snes/utils/damgsnes.c
[0]PETSC ERROR: DMMGSolve() line 372 in src/snes/utils/damg.c
[0]PETSC ERROR: main() line 270 in
/home/vyan2000/local/PPETSc/petsc-2.3.3-p15/src/ksp/ksp/examples/tutorials/NCprojectHeatProfile1D.c
application called MPI_Abort(MPI_COMM_WORLD, 62) - process 0[cli_0]:
aborting job:
application called MPI_Abort(MPI_COMM_WORLD, 62) - process 0

The error makes sense, since I did not pass in the analytical Jacobian for
the preconditioner matrix. In stead, I was using
DMMGSetSNESLocal(dmmg,FormFunctionLocal,0,ad_FormFunctionLocal,admf_FormFunctionLocal).
I am going to change the code a bit, pass in the analytical Jacobian and do
the -snes_type test.

I will bear your suggestion in mind during the test.

Thanks a lot,

Yan



>
>   Barry
>
>
>
>> Thanks a lot,
>>
>> Yan
>>
>> On Sun, Jan 10, 2010 at 4:35 PM, Barry Smith <bsmith at mcs.anl.gov> wrote:
>>
>>  You already got a 10^16 drop in the residual norm. It is not realistic to
>> expect to get much more than that for double precision calculations. Perhaps
>> your original F() has some funky scaling of different components that you
>> can fix.
>>
>>
>>
>>  Barry
>>
>>
>> On Jan 10, 2010, at 2:55 PM, Ryan Yan wrote:
>>
>> Hi All,
>> I am solving a nonlinear system using snes. The -snes_monitor option has
>> the following output:
>>
>>  0 SNES Function norm 2.640163923729e+09
>>  1 SNES Function norm 1.047643565314e+08
>>  2 SNES Function norm 1.712732074788e+06
>>  3 SNES Function norm 1.002169173269e+04
>>  4 SNES Function norm 1.655878303433e+03
>>  5 SNES Function norm 3.746498305706e+02
>>  6 SNES Function norm 8.317435704773e+01
>>  7 SNES Function norm 1.857639969641e+01
>>  8 SNES Function norm 4.149691057773e+00
>>  9 SNES Function norm 9.265604042412e-01
>>  10 SNES Function norm 2.069527103214e-01
>>  11 SNES Function norm 4.624186491082e-02
>>  12 SNES Function norm 1.035558432688e-02
>>  13 SNES Function norm 2.341362958811e-03
>>  14 SNES Function norm 5.507445427277e-04
>>  15 SNES Function norm 1.485123568354e-04
>>  16 SNES Function norm 5.180043781814e-05
>>  17 SNES Function norm 2.341966514486e-05
>>  18 SNES Function norm 1.344936158651e-05
>>  19 SNES Function norm 1.054812641176e-05
>> Number of Newton iterations = 19
>> Converged reason is 4
>>
>> It looks like the iterate never falls into a quadratic convergence region
>> before it converges. Is there any hint to understand this behavior?
>>
>> Thanks a lot,
>>
>> Yan
>>
>>
>>
>>
>>
>
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