原文地址：https://www.cnblogs.com/liqinglucky/p/fourier.html
import matplotlib.pyplot as plt
import numpy as np
t = np.arange(-2*np.pi, 2*np.pi, 0.01)
s =(4*np.sin(t))/(np.pi)+(4* np.sin(3*t))/(3*np.pi)
plt.plot(t, s)
plt.xlabel('time (s)')
plt.ylabel('voltage (mV)')
plt.title('About as simple as it gets, folks')
plt.grid(True)
plt.savefig("test.png")
plt.show()
