  Lagrangian coherent structures are effective barriers, sticky regions, that
separate phase space regions of different dynamical behavior. The usual way to
detect such structures is via finite-time Lyapunov exponents. We show that
similar results can be obtained for single-frequency systems from finite-time
rotation numbers, which are much faster to compute. We illustrate our claim by
considering examples of continuous and discrete-time dynamical systems of
physical interest.
