title: Over-plot an equation curve over a png image
body: <p><a href="https://i.stack.imgur.com/E5l5w.png" rel="nofollow noreferrer">enter image description here</a>I'm having trouble overplotting a relation between radial velocity and offset(position). I've looked at various solutions, but it doesn't seem to work. I've converted the equation into numbers, with only one variable.It also doesn't display the picture to the required dimensions.</p>
  
  <pre><code>x = np.linspace(-0.8 ,0.8 , 1000)  
  
  y = 0.5*((1.334e+20/x)**0.5)
  
  img = plt.imread('Pictures/PVdiagram1casaviewer.png')
  fig, ax = plt.subplots(figsize=(16, 16), tight_layout=True)
  
  ax.set_xlabel('Offset(arcsec)', fontsize=14)
  ax.set_ylabel('Radial Velocity (Km/S)', fontsize=14)
  
  ax.imshow(img, extent=[-0.8, 0.8, -5, 15])
  ax.plot(x, y, linewidth=5, color='white')
  
  
  plt.title('PV Diagram')
  
  plt.show()
  </code></pre>
  
  <p><a href="https://i.stack.imgur.com/hNMw8.png" rel="nofollow noreferrer">enter image description here</a></p>