changes made:
1 added Ey field visualization
2 added custom force() to act only when inside the space between the 2 magnets and always in the direction of vy thus the frequency of Ey is simulated through the vy sign change.
3 added Ey vs time graph for visualizing the square wave in thanks to Nat Ng suggestion in facebook
4 added KE graph to check that ?KE after each linear path in the gap is constant.
24 Feb 2011
fix a bug on the visual of Bz
[code]if (Bzshow==true)sp[i]=true; // controller for drawing Bz
if (Bzshow==false)sp[i]=false; // completely off Bz visual
if (calF(xp[i],yp[i],1)==0)sp[i]=false; // if no Bz calculated, no draw
yp2[i]=-yp[i]; // duplicate for other magnet[/code]