title: Different y scales in one python plot
body: <p>I want to make a plot as the one attached</p>
  <p><a href="https://i.stack.imgur.com/TdgGd.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/TdgGd.png" alt="Plot" /></a></p>
  <p>Where it has two y axes with different scales and all the parameters names are identified by colors in the small upper left box.</p>
  <p>I tried the following</p>
  <pre><code>    plt.figure()
      p1, = plt.plot(s_pos, beta_x)
      p2, = plt.plot(s_pos, beta_y)
      plt.legend([p1, p2], [r'$\beta_x$', r'$\beta_y$'])
      p3, = plt.plot(s_pos, dx)
      plt.legend([p3], [r'$\eta_x$'])
  </code></pre>
  <p>But it showed the eta in the same scale of the plots (s_pos, betax, beta y) y axes and also it give me the eta only in the small box.</p>
  <p><a href="https://i.stack.imgur.com/zgb6V.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/zgb6V.png" alt="plot2" /></a></p>