Plot the chaotic solution of the periodically driven Fitzhugh–Nagumo system

(see Section 4.1)

˙u = 10 u − v −

u3 3 + I (t)

, ˙v = u − 0.8v + 0.7, where I (t) is a periodic step function of period 2.025, amplitude 0.267, and width 0.3.