I have written a function to calculate the Runge-Kutta numerical approximation of the differential equation dy/dt = -2ty^2 w/ initial conditions y(0)=1 from t=0 to t=10. The function worked when I ...

That'll do a DFS on your file structure, which might not be what you want. edit: err, yeah, his thing is the same, but uses your directory class (FYI: classes are usually capitalized).