title: What does the $\ symbol mean in Python code?
body: <p>I find below code from a book to show how to use matplotlib in Python. The code runs normally. But I don't understand what does the symbol $ or $\ mean here?</p>
  
  <pre><code># -*- coding: utf-8 -*-
  import numpy as np
  import matplotlib.pyplot as plt
  
  x = np.linspace(0, 10, 1000)
  y = np.sin(x) + 1
  z = np.cos(x**2) + 1
  
  plt.figure(figsize = (8, 4))
  plt.plot(x,y,label = '$\sin x+1$', color = 'red', linewidth = 2)
  plt.plot(x, z, 'b--', label = '$\cos x^2+1$')
  plt.xlabel('Time(s) ')
  plt.ylabel('Volt')
  plt.title('A Simple Example')
  plt.ylim(0, 2.2)
  plt.legend()
  plt.show()
  </code></pre>