[FLASH-USERS] Crashy restarts

[Anshu Dubey]

> Greetings all,
>
> I am trying to restart some of my Flash (v2.5 using the Intel 9.0
> compiler) runs, and I'm encountering unexplained crashes. The restart runs
> crash before they reach the same evolution time as the run from which they
> restarted. e.g.:
>
> Run a calculation for 1000 timesteps. As well as the initial and final
> checkpoints, there's one after 500 timesteps (say)
>
> Try to restart the code
>
> Code dies after 30-40 timesteps
>
> This happens whether I restart after the initial checkpoint, or the n=500
> one. Are checkpoints supposed to give exactly the same result (up to the
> last few bits, perhaps), or is there a difference between a restarted run,
> and one just left going. Looking at the code, calculation of the timestep
> might be slightly affected, but I don't see that that should be
> significant.

If you are using the code with conserved_var=.false. (the default mode)
the checkpoints should give exactly the same result. If
conserved_var=.true., there is an extra division and multiplication
introduced by the conversion of the variables, and that causes the number
to change a little bit, which if your problem is very non-linear, can
grow with time. But none of that explains the death from restart.
You could try dumping a few checkpoints in between so that you get
at least one from the restarted run to compare against a "from scratch"
run.

Anshu