A Lyapunov function for a Synchronisation diffeomorphism of three clocks

Lyapunov functions are essential tools in dynamical systems, as they allow the stability analysis of equilibrium points without the need to explicitly solve the system's equations. Despite their importance, no systematic method exists for constructing Lyapunov functions. In a previous paper, we examined a diffeomorphism arising from the problem of Huygens Synchronisation for three identical limit cycle clocks arranged in a line, proving that the system possesses a unique asymptotically stable fixed point on the torus T2, corresponding to synchronisation in phase opposition. In this paper, we re-derive this result by constructing a discrete Lyapunov function for the system. The closure of the basin of attraction of the asymptotically stable attractor is the torus T2, showing that Huygens Synchronisation exhibits generic and robust behaviour, occurring with probability one with respect to initial conditions.