Re: [Phys-l] Simulating a disturbance of a stable planetary system.

[John Denker <jsd@av8n.com>]

On 01/01/2008 08:19 PM, Ludwik Kowalski wrote:
> ..... The simulation software 
> I am using , I.P.,  seems to be highly reliable (consistent with 
> underlying physics). 

"Highly reliable"?  That statement would be more informative if
it were more specific and more quantitative:
 -- What tests have been run?
 -- Quantitatively, how good was the agreement with analytical
  results?
 -- Are these tests designed to be incisive?  What classes
  of bugs are they likely to detect?  Are they appropriate to 
  the numerical methods IP is actually using?
 -- What are the /limits/ of validity?
 -- How do we know that IP did not simply incorporate the
  analytic solution for simple cases?  (That's what I would
  have done.)  Doesn't that mean  that the results for non-
  simple cases will be incomparably less accurate?

> How to use such software to account for 
> unavoidable perturbations? The I.P. does not account for them.

Sure it can account for them.  

 *) For starters, you can run an ensemble of simulations, with 
  slightly different initial conditions.
 *) Also you can perturb a two-body problem by adding a relatively
  small third body.
 *) Et cetera.