[petsc-users] What could be the reason for a convergence history like this one?

[Jed Brown]

On Tue, 09 Feb 2010 13:21:22 -0500, "(Rebecca) Xuefei YUAN" <xy2102 at columbia.edu> wrote:
> Hi,
> 
> The SNES convergence history shows the residual increases or stop  
> decreasing starting at some iteration. I ran two different cases for  
> the same code, and the history looks similar, what could be wrong with  
> the code?

Perhaps a wrong or low-accuracy Jacobian?  Are you using an analytic
Jacobian?  Does the history change if you tighten the linear solve
tolerance?  If the system is very ill-conditioned, you might only be
able to converge this far.

Jed