title: Gnuplot, superimpose curves with splot
body: <p>I am trying to plot a family of curves in space using gnuplot.<br>
  I am trying to do it with <code>for</code>-loops. The data are in 4 columns, and every 20 rows, a new plot starts, e.g., if I do a plot using the 3 and 4 columns, on the row 21, the index in the third column starts again, and the number on the second column increases by one. This pattern repeats, and every 320 rows, the index on the first column increases by one, and all the pattern repeats itself again.<br>
  The index in the first column goes from 2.0 to 3.8 whereas the index on the second column goes from 75 to 90.<br>
  In my code I tried to set the range limits from 1.8 to 4.2 for one axis, and from 0 to 100 for the second axis.</p>
  
  <p>I wrote the following code </p>
  
  <pre><code>a=0 # this variable indicates how many rows to skip
  do for [j=20:38:1]{ # loop for the first column
  do for [i=75:90:1]{ # loop for the second column #
  splot [1.8:4.2][1:101] "dataforgnuplot" every ::a::a+19 u 1:3:4
       w lines title sprintf("%3.2f %3.2f",j/10.0, i);
  a=a+20;
  }
  }
  </code></pre>
  
  <p>and it generates one curve at a time, but the previous one disappears, I had a look at <code>multiplot</code>, and also was trying with <code>replot</code>, but, I still haven't found how to do that.</p>