get the derivative with ode45

Hello every one! I'm trying to solve a differential equation y' = f(t,y) with MATLAB ode45. Besides the original y, y' is also very useful to me. But I simply don't know how to get it. Is there any convenient method? Or what I can do is just to compute y in many point and use diff? Thank you very much!

Answer 1

[Jan]

ODE45 replies the arrays y(t_i) and t_i. You have defined the function y'=f(t, y). If f is defined such that it accepts vectors as input, getting y' should be trivial:

[t, y] = ode45(@f, ...)
yd = f(t, y)

[Albert]

Thanks Simon. I need y and y' to compute some functions and even do integral.I'm just afraid that if I ask ode45 to compute y in too many data points it would be very slow and the accuracy of following computations might be poor. If MATLAB can directly support this it'll be cool.