[petsc-users] Snes behavior

[Ryan Yan]

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?

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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