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On 12/29/2007 12:26 PM, Ludwik Kowalski wrote:
The situation, however, seems to be paradoxical. On one hand we know that undisturbed cycles are highly reproducible, on the other hand, we see that a disturbance-due change, for example in the period T, is not corrected after the disturbance is removed.
In physics, the definition of /chaos/ (i.e. deterministic chaos)
is extreme sensitivity to initial conditions.
So what is my point? I want to know how to use simulations, or any other simple method, in a disagreement about stability or instability
I suspect stability and instability are the wrong concepts, or at least the wrong terminology.
You might be much better off asking about chaotic versus non-chaotic.
There are simple yet powerful ways of studying chaotic systems, and
studying the transition from order to chaos. This was very trendy
in the 1980s. http://www.pa.msu.edu/~bauer/applets/Chaos-Feigenbaum/feig.html
Once you understand what chaos is, the three-body orbit problem is easily shown to be chaotic:
Since the Subject: line asks about numerical simulations: it is
super-easy to get into a situation where a physics /simulation/
is numerically unstable, even if the underlying physics is well
There are many bugs that can crop up in a numerical simulation,
which we can discuss if anybody is interested.
The Kepler problem is a remarkably good incubator for such bugs.
This is partly because we have such a good analytical (non-
numerical) solution to the problem. Numerical methods that are not specifically tuned to this problem are almost guaranteed to get the wrong answer. Energy won't be conserved, angular momentum
won't be conserved, and/or the orbital axis will precess when it shouldn't.
These bugs can be dealt with to some extent, but the overall
problem is still a topic of research
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