[petsc-users] How do I know it is steady state?

[Barry Smith]

> On Oct 30, 2015, at 12:23 PM, Zou (Non-US), Ling <ling.zou at inl.gov> wrote:
> 
> Hi All,
> 
> From physics point of view, I know my simulation converges if nothing changes any more.
> 
> I wonder how normally you do to detect if your simulation reaches steady state from numerical point of view.
> Is it a good practice to use SNES convergence as a criterion, i.e.,
> SNES converges and it takes 0 iteration(s)

   Depends on the time integrator and SNES tolerance you are using. If you use a -snes_rtol 1.e-5 it will always try to squeeze 5 MORE digits out of the residual so won't take 0 iterations even if there is only a small change in the solution. 
> 
> Thanks,
> 
> Ling