[petsc-users] Snes behavior
Ryan Yan
vyan2000 at gmail.com
Sun Jan 10 15:28:05 CST 2010
Hi Matt,
Thank you very much for the suggestion. I was using
DMMGSetSNESLocal(dmmg,FormFunctionLocal,0,ad_FormFunctionLocal,admf_FormFunctionLocal),
so the Jacobian is calculated by automatic differentiation, right? For this
instance, is there any way to check the correctness of the set up of the
residual?
After I tried the -snes_mf the linear solver failed( ):
0 SNES Function norm 1.578681107621e+08
1 SNES Function norm 1.343502549866e+08
2 SNES Function norm 1.211729760183e+08
3 SNES Function norm 1.211728837635e+08
4 SNES Function norm 1.211728837178e+08
5 SNES Function norm 1.211728837177e+08
0 SNES Function norm 1.999574234301e+08
0 SNES Function norm 1.677632378801e+08
Number of Newton iterations = 0
Converged reason is -3
Might it be helpful to call DMMGGetSNES and then setup the analytical
jacobian for the preconditioner matrix? My residual is pretty
straightforward though.
Yan
On Sun, Jan 10, 2010 at 3:59 PM, Matthew Knepley <knepley at gmail.com> wrote:
> It is possible for the radius of quadratic convergence to be very small.
> However, I
> would check your Jacobian, and maybe try -snes_mf.
>
> Matt
>
>
> On Sun, Jan 10, 2010 at 2:55 PM, Ryan Yan <vyan2000 at gmail.com> 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
>>
>>
>>
>
>
> --
> 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
>
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