title: matplotlib simple and two head arrows
body: <p>I would like to make a simple arrow and a two head arrow. I used the following to make a simple arrow, but I doubt this is the easiest method :</p>
  <pre class="lang-py prettyprint-override"><code>import matplotlib.pyplot as plt
  arr_width = .009   #  I don't know what unit it is here.
  fig = plt.figure()
  ax1 = fig.add_subplot(111)
  ax1.plot(range(10))
  ax1.arrow(1, 1, 0, .5, width = arr_width, head_width = 3 * arr_width, 
            head_length = 9 * arr_width)
  plt.show()
  </code></pre>
  <p>I can't find how to make two head arrows with this method.</p>