title: Matplotlib quiver shape inverted triangle
body: <p>I am looking for a way to make an inverted triangle vector plot
  <a href="https://i.stack.imgur.com/RlE5U.png" rel="nofollow noreferrer">Intended Image</a></p>
  <p>I have tried using <code>matplotlib quiver</code> to replicate what I want. But it didn't work</p>
  <pre><code>import matplotlib.pyplot as plt
  import numpy as np
  u = v = 0.5
  length = np.sqrt(u**2 + v**2)
  data = np.array([[1, -1], [-1, -1]])
  origin = np.array([[0.5, 9.5], [9.5, 9.5]])
  width=0.005
  hal = hl = 0.1 / width * length
  plt.quiver(*origin, data[:, 0], data[:, 1], angles='xy', scale_units='xy', scale=2, 
             headwidth=hl,
             headaxislength=hal,
             headlength=hl,
             width=width)
  
  
  img = plt.imread(&quot;TEST.png&quot;)
  plt.imshow(img,zorder=0, extent=[0, 10, 0, 10])
  plt.show()
  </code></pre>
  <p>I have reached the point where only the head remained, but when i invert it resulted in</p>
  <p>Head only:</p>
  <p><img src="https://i.stack.imgur.com/zxIg1.png" alt="Current" /></p>
  <p>Inverted (<code>headlength = -hl</code>):</p>
  <p><img src="https://i.stack.imgur.com/LWEUS.png" alt="Result" /></p>
  <p>Can anyone tell me what i am missing or maybe there's another way to make this?</p>