[petsc-users] Snes behavior

[Ryan Yan]

Hi Matt,
Thanks,

On Sun, Jan 10, 2010 at 4:34 PM, Matthew Knepley <knepley at gmail.com> wrote:

> On Sun, Jan 10, 2010 at 3:28 PM, Ryan Yan <vyan2000 at gmail.com> wrote:
>
>> 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?
>>
>
> Not unless you have ADIC configured. Do you see the AD code?
>
>

I did not have AD code configured when I was installing PETSc. I will leave
this option till later for the test.



> 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
>>
>
> Yes, since there is no preconditioner. However, just use GMRES and a very
> large subspace.
>
>
Sorry, but what do you mean by use a very large subspace? I would try this.

Yan


>   Matt
>
>
>> 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
>>>
>>
>>
>
>
> --
> 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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