Paper detail

Number of first-passage times as a measurement of information for weakly chaotic systems

We consider a general class of maps of the interval having Lyapunov subexponential instability $|δx_{t}|\sim|δx_{0}|\exp[Λ_{t}(x_{0})ζ(t)]$, where $ζ(t)$ grows sublinearly as $t\rightarrow\infty$. We outline here a scheme [J. Stat. Phys. {\bf 154}, 988 (2014)] whereby the choice of a characteristic function automatically defines the map equation and corresponding growth rate $ζ(t)$. This matching approach is based on the infinite measure property of such systems. We show that the average information that is necessary to record without ambiguity a trajectory of the system tends to $\langleΛ\rangleζ(t)$, suitably extending the Kolmogorov-Sinai entropy and Pesin's identity. For such systems, information behaves like a random variable for random initial conditions, its statistics obeying a universal Mittag-Leffler law. We show that, for individual trajectories, information can be accurately inferred by the number of first-passage times through a given turbulent phase space cell. This enables us to calculate far more efficiently Lyapunov exponents for such systems. Lastly, we also show that the usual renewal description of jumps to the turbulent cell, usually employed in the literature, does not provide the real number of entrances there. Our results are supported by exhaustive numerical simulations.