title: How to change the head size of the double head annotate in matplotlib?
body: <p>Below figure shows the plot of which arrow head is very small...
  <a href="https://i.stack.imgur.com/GvRgT.jpg" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/GvRgT.jpg" alt="enter image description here"></a></p>
  
  <p>I tried below code, but it didnot work...
  it said "    raise AttributeError('Unknown property %s' % k)
  AttributeError: Unknown property headwidth"...</p>
  
  <pre><code>xyfrom=[10,620]
  xyto=[130,620]
  ax.annotate("",xyfrom,xyto,arrowprops=dict(arrowstyle='&lt;-&gt;',linewidth = 2,     headwidth=10,color = 'k'
  ))
  ax.text((xyto[0]+xyfrom[0])/2-15,(xyto[1]+xyfrom[1])/2+10,"headwidth is too    small",fontsize=24)
  </code></pre>