That sounds really nice, perfect competition for this game, unfortunately I am not a US citizen.

I wrote it all myself, the code you would be interested is in PolishNotationFunction.java . It is mostly not specific to the game and would probably be easy to use on your own code with minimal modifications. The functions supported are:

sqrt()
log()
ln()
abs()
sin()
cos()
tan()
exp()

and the operators are: + - / * ^

Adding new functions would also be simple, I had actually a few more functions implemented but decided to remove from the game, like hyperbolic sines. Adding new operators would be much more complex.

Graphwar is an artillery game in which you must hit your enemies using mathematical functions. The trajectory of your shot is determined by the function you wrote, and your goal is to avoid the obstacles and your teammates and hit your enemies. The game takes place in a Cartesian Plane.

It's an applet and I have a website for it: www.graphwar.com

Up to 10 players can play online and it is also possible to play against a computer, but be careful, the computer is really good so try to play against very low levels (around 10) in the beginning.

There is a tutorial and I recommend reading it to understand how to play: http://www.graphwar.com/tutorial2.html

The code is open source and released under the GPL and is available on the website.

Cheers