title: Empty plot... using for loop to create plot
body: <pre><code>import matplotlib.pyplot as plt
  import numpy as np
  G=6.674e-11 #gravitational constant
  Mb=1.591e41 #mass of bulge
  ps=1.616e-19 #density of stellar system
  pd=4.041e-18 #density of dark matter halo
  Rc=6.171e19 #Radius at 2kpc in meters
  for i in np.arange(0, 6.172e19, 1e19):
      v = (np.sqrt(ps*(4/3)*np.pi*(i**2)*G))
      print(i)
      print(v)
      plt.plot(i, v, color='red')
  plt.show()
  </code></pre>
  
  <p>This is giving me an empty plot. Not sure why. I've tried various techniques to no avail. Is there a function I'm missing?</p>