[petsc-users] Snes behavior

[Barry Smith]

   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
>
>