title: Plotting with multiple Y-axes
body: <p>When using <code>ax.&lt;plot_function&gt;</code> for plotting objects on a figure. How can I <code>"hold on"</code> the plot and 
  render multiple plots on the same plot?</p>
  
  <p>For example:</p>
  
  <pre><code>f = plt.figure(figsize=(13,6))
  ax = f.add_subplot(111)
  
  ax.plot(x1,y1)
  ax.plot(x2,y2)
  
  ax.plot(xN,yN)
  </code></pre>
  
  <p>I have tried adding:</p>
  
  <pre><code>ax.hold(True)
  </code></pre>
  
  <p>before I start plotting, but it doesn't work. I think the problem is that they all share the same y-scale and I only see the plot with the largest range of values.</p>
  
  <p>How can I plot multiple 1D arrays of different scales on the same plot? Is there any way to plot them with different Y-axis next to each other?</p>