title: What are set_xlim() and set_ylim() in matplotlib?
body: <p>Here is the question about applying some limits on x and y axis of the canvas. 
  I have found the function for limits but I am not getting their purpose. What are they used for?  </p>
  
  <pre><code>fig1 = plt.figure()
  ax0 = fig1.add_axes([0,0,1,1])
  ax1 = fig1.add_axes([0.2,0.5,.4,.4])
  ax0.set_xlabel('X')
  ax0.set_ylabel('Z')
  ax1.set_xlabel('X')
  ax1.set_ylabel('Z')
  
  
  #problem Area
  ax1.set_ylim(30,50)
  ax1.set_xlim(20,22)
  
  
  ax0.plot(x,z)
  ax1.plot(x,y)
  </code></pre>