# [petsc-users] Snes behavior

Matthew Knepley knepley at gmail.com
Sun Jan 10 14:59:07 CST 2010

```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