说明：  Exercise 1 The following differential equations describe the Van der Pol oscillator dx/dt = μ(x − 1/3x3− y) (1) dy/dt = (1/μ)x Set μ = 1 and simulate the behaviour of this system. Illustrate the fact that, for non-zero values of the initial conditions, the states of the system converge to a limit cycle. Identify the period of the trajectories on the limit cycle. Show that if μ is increased then the limit cycle becomes more elongated.