title: Fill Between Two Polar Curves with matplotlib fill_between
body: <p>I have a feeling I'm going to be smacking my forehead on this one, but I'm trying to fill the <em>common interior</em> of two polar functions <code>r = 4 sin(2θ)</code> and <code>r = 2</code>.  It seems I'm getting the opposite of what I want.  Any ideas?</p>
  
  <pre><code>import numpy as np
  import matplotlib.pyplot as plt
  
  theta = np.arange(0, 2, 1./180)*np.pi
  r = abs(4*np.sin(2*theta))
  r2 = 2 + 0*theta
  
  plt.polar(theta, r, lw=3)
  plt.polar(theta, r2, lw=3)
  plt.fill_between(theta, r, r2, alpha=0.2)
  plt.show()
  </code></pre>
  
  <p><img src="https://i.imgur.com/WQKGstp.png" alt="Polar Plot"></p>