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

[Philipp Moesta]

Hi Erik,

I believe Dana ran into similar problems a while back for some tests using CTGamma (not sure if that is related at all, as I don't remember the details anymore). But maybe this can be of help.

Philipp

On Feb 28, 2012, at 5:48 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
> 
> -- 
> Erik Schnetter <schnetter at cct.lsu.edu>
> http://www.perimeterinstitute.ca/personal/eschnetter/
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