plt.subplot(111)
line = plt.plot(t2, np.cos(2*t2*np.pi), lw=2)
plt.grid()
plt.annotate('local max', xy = (2,1), xytext = (3,1.5),
            arrowprops = dict(facecolor='blue', shrink = 0.05))
plt.ylim(-2,2)