Slow Passage through a Saddle-Node Bifurcation in Discrete Dynamical Systems.

We study a discrete non-autonomous system whose autonomous counterpart (with the frozen bifurcation parameter) admits a saddle-node bifurcation, and in which the bifurcation parameter slowly changes in time and is characterized by a sweep rate constant $\epsilon$. The discrete system is more appropriate for modeling realistic systems since only time series data is available. We show that in contrast to its autonomous counterpart, when the time mesh size $\Delta t$ is less than the order $O(\epsilon)$, there is a bifurcation delay as the bifurcation time-varying parameter is varied through the bifurcation point, and the delay is proportional to the two-thirds power of the sweep rate constant $\epsilon$. This bifurcation delay is significant in various realistic systems since it allows one to take necessary action promptly before a sudden collapse or shift to different states. On the other hand, when the time mesh size $\Delta t$ is larger than the order $o(\epsilon)$, the dynamical behavior of the solution is dramatically changed before the bifurcation point. This behavior is not observed in the autonomous counterpart. Therefore, the dynamical behavior of the system strongly depends on the time mesh size. Finally. due to the very discrete feature of the system, there are no efficient tools for the analytical study of the system. Our approach is elementary and analytical.