title: Multiple x-axis, which are nonlinear to each other
body: <p>I am trying to plot a figure with two x-axis, which are non-linear to each other, with matplotlib. The plot I want to get is like this:</p>
  
  <p><img src="https://i.stack.imgur.com/88llX.gif" alt="Plot"></p>
  
  <p>Basically, the age is dependent on red shift. It's non linear and need to be calculated. I want to make both age and red shift as x-axis. How can I make it?</p>