(48G 49G 50G) Runge-Kutta Diff Eqn solver

[rcthacker]

I would like to use the Runge-Kutta-Fehlberg function/solver for second order nonlinear DE's. It works fine for first order NL equations, and for second order linear equations. However, I can't figure out how to use the matrix (function) - vector (solution) multiplication to include nonlinear dependent variables. For example, y' = v, and y'' = g - k X v^2. (the skydiver problem from calculus). BTW, the 50G User Guide discusses first order linear equations, but solves a first order nonlinear equation (SQRT(V)).

Any recommendations for further reading on the use of this powerful function?