title: Common main title of a figure panel compiled with par(mfrow)
body: <p>I have a  compilation of  4 plots drawn together with <code>par(mfrow=c(2,2))</code>. I would like to draw a common title for the 2 above plots and a  common title for the 2 below panels that are centered between the 2 left and right plots. </p>
  
  <p>Is this possible?</p>