[ODE] Iterative solution

[Martin C. Martin]

> Right now, I'm running at 5 iterations

Why not iterate until values change by less than some specified amount? 
You should also have a maximum number of iterations as well, but it can be
(much?) higher than 5.

> while the
> old solution plummets to fractional framerates, and eventually segfaults
> without an error (on my machine at least.... I think it has something to
> do with compiling the operating system and all my packages with -O3
> optimizations).

If you're using cygwin, this probably has something to do with setting the
stack size.

> Another thing that's probably slowing it down a good bit is the fact that
> collision detection has to be run before every iteration.

It sounds like you're generating the constraints anew between every
iteration.  Why not just keep the same constraints?

> expected.  However, if the cars move forward and get under the block
> before it touches down, even the iterated solution slows down by a factor
> of 10 or more (the old solution still craps).  I thought the iterated
> solution shouldn't have this problem.

Well, you're generating more contacts, so that's part of it.  Collision
detection takes a variable amount of time, so I'm guessing that's the
rest.