[ODE] 2d system

[Christopher Jefferson]

Hi again!

OK, update on my attempt at making a 2d ODE system :) (sorry if this is 
beginning to bore people, feel free to tell me to stop..)

My current plan is as follows:

1) Write 2D API which is the same as 3d API and then simply forward all 
requests through to the 3D API with z=0: done
2) Write many test cases for this API: in progress
3) slightly alter all the 3d api code so that the vectors,matrices,etc are 
contained in classes (mainly so I can do bounds checking on the arrays to 
see what is reading/writing the 3rd dimension): in progress
4) (the main step!) Go through the existing code function by function 
"2d"ising as much of the code as possible, and then see whats left! : just 
started!

Just because I'm sure there are some people here with much better physics 
than me...

1) Is there anything that jumps to mind I should watch out for if I want to 
use the 3d code as a sudo-2d code by just only two of the dimensions
2) Any good guides to inertia matrices, in both 2 and 3 dimensions? I've 
been re-reading all my physics notes (good fun!) and that's the only bit 
I'm not 100% happy with...

bye for now,
Chris