[petsc-users] Snes failled with reason -6

[Que Cat]

Hi Barry,

Thanks for your exlanation. I used -snes_mf -pc_type lu and now it failed
with reason -3 (/* the linear solve failed */). So, something is wrong with
the function.


On Thu, Dec 19, 2013 at 5:01 PM, Barry Smith <bsmith at mcs.anl.gov> wrote:

>
>   ratio is || A - Afd || /||A|| where |||| is the frobenus norm and
> difference is || A - Afd ||.
>
>   Try using -snes_mf -pc_type lu
>
>    This can often converge even if the A you provide is wrong, so if this
> convergence sine then likely the Jacobian is wrong.
>
>    It is also possible that the function evaluation has a bug.
>
> http://www.mcs.anl.gov/petsc/documentation/faq.html#newton
>
>
>    Barry
>
>
>
> On Dec 19, 2013, at 4:26 PM, Que Cat <quecat001 at gmail.com> wrote:
>
> > Hello,
> >
> > I use SNES to solve the non linear coupled equations. I have checked the
> hand-coded jacobian with -snes_type test and received the result:
> > Norm of matrix ratio 1.39606e-23 difference 1.53372e-14 (user-defined
> state)
> > Norm of matrix ratio 3.03157e-10 difference 0.33305 (constant state -1.0)
> > Norm of matrix ratio 3.03157e-10 difference 0.33305 (constant state 1.0)
> > It said that "  if the ratio is O(1.e-8), the hand-coded Jacobian is
> probably correct." What is the second paramenter "difference 1.53372e-14
> ...."? Does it play any role in checking the accuracy of hand-coded
> jacobian?
> >
> > The SNES solver for failed with the reason -6 "the line search failed".
> I tried with all other line search method stated in the PETSC manual, but
> they all failed.
> >
> > I tried to figure out what is wrong with my code? Could you please give
> me any recommendation to direct me how to check my code? I appreciate your
> help.
> >
> > QUe
> >
>
>
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