[petsc-users] Snes behavior

[Matthew Knepley]

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?


> 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.

  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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