title: How to draw axis in the middle of the figure?
body: <p>I want to draw a figure in matplotib where the axis are displayed within the plot itself not on the side</p>
  
  <p>I have tried the following code <a href="http://squall0032.tumblr.com/post/77300791096/plotting-a-sigmoid-function-using" rel="noreferrer">from here</a>:</p>
  
  <pre><code>import math
  import numpy as np
  import matplotlib.pyplot as plt
  
  def sigmoid(x):
      a = []
      for item in x:
          a.append(1/(1+math.exp(-item)))
      return a
  
  x = np.arange(-10., 10., 0.2)
  sig = sigmoid(x)
  
  plt.plot(x,sig)
  plt.show()
  </code></pre>
  
  <p>The above code displays the figure like this:<br>
  <a href="https://i.stack.imgur.com/IYMGR.png" rel="noreferrer"><img src="https://i.stack.imgur.com/IYMGR.png" alt=""></a></p>
  
  <p>What I would like to draw is something as follows (<a href="https://en.wikipedia.org/wiki/File:Gjl-t(x).svg" rel="noreferrer">image</a> from Wikipedia)</p>
  
  <p><a href="https://i.stack.imgur.com/LHwY1.png" rel="noreferrer"><img src="https://i.stack.imgur.com/LHwY1.png" alt=""></a></p>
  
  <p>This <a href="https://stackoverflow.com/questions/5394527/how-to-draw-an-axis-in-the-middle-of-the-figure-using-matplotlib">question</a> describes a similar problem, but it draws a reference line in the middle but no axis.</p>