[ODE] Re: Different simulation results with different versions ofVisual C++?

[John Donovan]

> Have others found a way to work around this problem?  I need *exactly*
the same results from one simulation to another.

I haven't found a workaround, but I did notice the same problem when
running the same simulation twice at the same time. It all started
because I was gettinga diverging simulation with two slightly different
algorithms. So to see where it was diverging I created two worlds,
loaded the same data and rendered them simultainously. My problem turned
out to be a contact parameter issue and I fixed it quickly. But I then
noticed that running the two worlds _still_ diverged when run
simultainiously, but were identical when run individually. Because it
didn't really affect me I didn't bother following it up. But the only
conclusion I could come to was the random number generator was working
twice as hard when run in tandem, so generating slightly different
contact results.
So my advice would be to look at the RNG (there was some discussion on
it a while back on this list), and see if it is producing the same
results for each build.
Also, are you're running with a fixed timestep? With the different
optimisations from each compilier, you could well get a different
framerate every time.

-J

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