[Users] Can't evolve Minkowski with RK4 integrator?

[Yosef Zlochower]

MoL RK4 should reproduce generic RK4. The only difference
should be that MoL RK4 is more efficient with memory.

On 02/28/2012 08:48 PM, Erik Schnetter wrote:
> I've just encountered a strange problem: I can't evolve Minkowski with
> MoL's RK4 integrator. Small errors in K grow from floating-point
> round-off, and the simulation quickly goes bad. The error grows slowly
> (but measurably) in unigrid, but much faster with mesh refinement.
>
> For example, with unigrid the lapse grows by about 10^-15 every ten
> time steps or so; with mesh refinement, the simulation dies after a
> few ten time steps.
>
> However, things are fine with other time integrators, in particular
> with the generic RK1 and RK4 integrators.
>
> I've looked at other things as well, e.g. the CFL factor, the
> McLachlan implementation, the gauge parameters, dissipation, but could
> not find anything else that made a difference.
>
> Is there something bad about the RK4 integrator? Is it intrinsically
> unstable, more so than other RK schemes? Or did it break in some of
> the recent changes?
>
> -erik
>


-- 
Dr. Yosef Zlochower
Center for Computational Relativity and Gravitation
Assistant Professor
School of Mathematical Sciences
Rochester Institute of Technology
85 Lomb Memorial Drive
Rochester, NY 14623

Office:74-2067
Phone: +1 585-475-6103

yosef at astro.rit.edu

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