[ODE] reverse timestep?

[Mike Reinstein]

Actually, there is a way you could implement reverse time stepping, but it 
would require you to develop a wrapper for ODE. The wrapper would basically 
just pass all the data to ODE functions, and log the time each function was 
called along with the parameters. So basically you'd have a list ODE calls 
along with their respective timestamp. By taking this list and traversing it 
in reverse order, you could theoretically execute the calls in reverse, and 
negate the values of parameters. I don't know how this would work in 
practice...there are some other issues, for example youd have to ensure that 
you dont accumulate rounding error by playing/rewinding over and over, and 
you would have to make sure the ODE functions are called as close to the 
original timestamp values as possible. But I don't see anything that would 
prohibit this from being done.  Any thoughts on this folks?

-neko



>From: "Jon Watte" <hplus-ode at mindcontrol.org>
>To: "Tyler Streeter" <tylerstreeter at yahoo.com>, 
<ode at q12.org>
>Subject: RE: [ODE] reverse timestep?
>Date: Mon, 3 May 2004 08:51:34 -0700
>
>
>I don't think this is generally possible. When a body collides with more 
than one other body during a timestep, I don't see how it's generally 
possible to analytically know how much of the respective 
velocities/momentums came from where. That, and the floating point 
imprecision would kill you ;-)
>
>Cheers,
>
>			/ h+
>
>
>-----Original Message-----
>From: ode-bounces at q12.org [mailto:ode-bounces at q12.org]On Behalf Of Tyler
>Streeter
>Sent: Monday, May 03, 2004 8:15 AM
>To: ode at q12.org
>Subject: [ODE] reverse timestep?
>
>
>Is it possible to run a simulation in reverse?  I was
>wondering if I could run my simulation for a while,
>then run it backwards from the end to the beginning.
>
>I thought maybe you could simply reverse the direction
>of all forces, torques, and velocities.  Would that
>work, or is there a lot more to it?  If it were that
>simple, it would be nice to add this functionality to
>ODE and be able to just pass a negative timestep to
>the solver and have it do this automatically.
>
>Tyler Streeter
>
>
>
>
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