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

[Zou (Non-US), Ling]

Barry, thanks. True and not true.
SNES can converge under other conditions, such as SNORM condition, e.g.,

Solving time step 300, using BDF1, dt = 0.1.

Current time (the starting time of this time step) = 29.85.

        NL step =  0, SNES Function norm =  5.49192E-04

Nonlinear solve converged due to CONVERGED_SNORM_RELATIVE iterations 0

In this case, snes_rtol is ignored.

Ling


On Mon, Nov 2, 2015 at 6:29 PM, Barry Smith <bsmith at mcs.anl.gov> wrote:

>
> > 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
>
>
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