Hi everybody,

I’m trying to solve a system of ODE which is exactly as the Lotka Volterra systems:

dx/dt = axy - bx

dy/dt = -cxy + dy

In which a, b, c, d, x(0) and y(0) are all positive. According to this set up, x(t) and y(t) could get really small but never become negative. I increased the abs error and rel error to both 10^(-12) and the number of iterations to 10000 which are both way beyond the default values but still get negative results. Does anybody have any suggestions for this problem? Thanks :)