title: Gnuplot pm3d plotting from file
body: <p>I'm having a problem with pm3d. I have data in the format <code>x y # # # #</code>, and I want to add the four #'s and plot their sum versus x,y with something like this:</p>
  
  <pre><code>set pm3d map
  splot 'data' 1:2:($3 + $4 + $5+ $6)
  </code></pre>
  
  <p>I've made sure that my data has lines wherever the first number changes, but I'm getting the  error: </p>
  
  <blockquote>
    <p>';' expected</p>
  </blockquote>
  
  <p>after <code>data</code>. If I get rid of everything after <code>data</code> then gnuplot is able to plot, but of course the plot is not what I want.</p>