Hints for coding

• When debugging, print out intermediate values. It's almost impossible to debug a code by looking at it--the code will almost always win a `staring contest.'
• Validate code with SIMPLE CASES. Validate early and often.

The number one mistake is using a too complex a system to test. For example , if you are computing particles in a potential in a box, try removing the potential--you should get particles in a box. And start with one particle, then two, then three... Don't start with eight particles.