HAM: A PHYSICS SIMULATION FRAMEWORK

Ham is a physics simulation framework that takes a Lagrangian of a
system and a description of how to render it and produces a real-time,
Hamiltonian-based simulation of the system.  It uses Maxima for the
symbolic mathematics and SDL2 for the graphics.

For example, for a simple harmonic oscillator:

	(define-simulation simple-harmonic-oscillator
	  :lagrangian (- (* 1/2 m (^ (dot q) 2)) (* 1/2 k (^ q 2)))
	  :coords (q)
	  :render (translate (* q 100) 0 (circle 20 0 0))
	  :start (q 1.0 p_q 0.0)
	  :params (m 1.0 k 2.0))

To then run the simulation:

	(make-instance 'simple-harmonic-oscillator)


								SETUP

If you have :sdl2 available and the sources are in ASDF's registry,
loading the system should just work™:

	(asdf:load-system :ham)

Otherwise, the full process fetching :sdl2 with Quicklisp and adding
the current directory to ASDF's registry is

	(ql:quickload :sdl2)
	(push *default-pathname-defaults* asdf:*central-registry*)
	(asdf:load-system :ham)

As it stands the system will only work with SBCL, though I don't think
it would be *that* much work to get it working with other Common Lisp
implementations.

Maxima ended up being a bit of a pain to build fully within ASDF so
the ASDF config first compiles it with its autotools set-up (so you'll
need autoconf et al) and uses the FASLs from that build when possible.
It's a little cursed but it does the job.  I did have to call
asdf::mark-operation-done directly so it might break with future
versions of ASDF (I'm using version 3.3.1 at time of writing).