Lyapunov function

A Lyapunov function is used to describe the behavior of a system. It is like a big "score" that tells us how complicated the system is acting. It works by looking at how much the different parts of the system are changing over time. If there are many changes it means the system is behaving complexly and the Lyapunov function will give a high score. If there are not many changes then the system is behaving simply and the Lyapunov function will give a low score.