[quote author=Fu-Kwun Hwang link=topic=178.msg5585#msg5585 date=1268991795]
I would suggest you use Runge-Kutta 4th order method for most of the cases.
The error could be due to numerical method. However, it could be due to the coding.

i was analyzing the codes and realized
[code]public double getA (int i,double[] v) {
if(i==0)return 0; // b*v[0]; i removed the b*v[0]; because original used a speed decay constant b = -.25 i think
else return 0;

after i change it to return 0, the TKE is constant now!
cool! so it was the coding.
for your info.