[ODE] Repeatable results with stepfast?

[Adam D. Moss]

Tyler Streeter wrote:
> I heard that StepFast uses random numbers internally,
> so I have been using WorldStep to get repeatable
> results.  It would be nice to use StepFast, though, to
> get the speed improvements.
> 
> Can anyone verify whether StepFast should
> theoretically give repeatable results? 

No, it won't, unless you reseed the PRNG.

 > What are the
> random numbers used for?

Reordering the order in which constraints are resolved,
to propogate the error around more fairly on average.

There's a #define for turning off the random re-ordering,
but it's not recommended.  Reseed the PRNG before each
step, instead.

--Adam
-- 
Adam D. Moss   . ,,^^   adam at gimp.org   http://www.foxbox.org/   co:3
"At this point the rocket becomes engorged with astronauts."