title: How to do a multi-tile plot with layout
body: <p>I want to plot four of the following in an <code>par(mfrow=c(2,2))</code>..</p>
  
  <pre><code>layout(matrix(1:2,ncol=1),widths=1,heights=c(2,2),respect=FALSE)
  par(mar = c(0, 4.1, 4.1, 2.1))
  plot(rnorm(100),main="Hi",type='l',ylab='',xaxt='n')
  par(mar = c(4.1, 4.1, 0, 2.1))
  plot(rnorm(100),main="",xlab="Hi",type='l',ylab='')
  </code></pre>
  
  <p>Therefore what I'm looking for is a total of 8 plots; 4 tiles of the above double plot. Yet if I precede the above with par(mfrow=c(2,2)) and run the above four times, it will simply generate a new plot each time, overwriting the call to <code>mfrow</code>. </p>
  
  <p>How can I adjust the above code such that it works with <code>par(mfrow=c(2,2))</code>?</p>