If the points are noisy, try a Savitzky-Golay - You can find the algorithm in Numerical Methods. It will always be 2 points behind your data (it needs 5 points to work), and can't get started before you acquire the fifth data point. It will smooth out noisy derivatives, but fast changes are also smoothed out. The change will be spread over the 5 data points in a sample.
Fabio wrote in message <email@example.com>... >Can anybody help me to find some numerical algorithm to compute numerical >derivatives ? > >PS: I must compute numerical derivatives to obtain velocity and acceleration >from numerical sample of displacement and I must do it in a real time >application. > >