title: How to output a file in gnuplot multiplot mode?
body: <p>I am plotting graphs in gnuplot (version 4.6 patchlevel 5) multiplot mode, which are being updated using reread.</p>
  
  <pre><code>set multiplot layout 3, 3
  do for [planeIter=4:10:3] for [ringIter=0:20:10] {
      plot for [quadIter=0:90:30] path/to/file \
      using 1:(column(1 + planeIter + ringIter + quadIter)) notitle
  }
  pause 10
  reread
  </code></pre>
  
  <p>Previously, I have outputted png files using:</p>
  
  <pre><code>set terminal pngcairo dashed enhanced
  plot path/to/file using 1:2
  set output 'foo.png'
  </code></pre>
  
  <p>But I haven't been able to find how to output a file of the latest multiplot screen.  Please would you tell me how I could do this?  Thank you.</p>