[petsc-users] Snes failled with reason -6

[Barry Smith]

  Run with

   -snes_mf_operator -pc_type lu  

   I’m sorry I sent the wrong instructions before.

   Barry

On Dec 20, 2013, at 7:54 AM, Que Cat <quecat001 at gmail.com> wrote:

> 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
> >
> 
>