1. Random signals

Example: let's assume that wind speed is observed using an anemometer over a given period of time. It is also assumed that the atmosphere is not very disturbed, and that the velocity is therefore subject to low-amplitude variations. Despite these assumptions, the results of these measurements can hardly be modelled by a function or even a linear or non-linear recurrent equation, even one with many coefficients. It may also be noted that observing the breeze for one hour, from t _1...