Adding a legend

The legend refers to the block of information printed on the graph (or occasionally outside it) that explains which curve or symbol is associated with which quantity. It is called a key in gnuplot. A legend or some device that conveys the equivalent information is essential when the graph displays more than one curve.

You've probably noticed that all of our example graphs already contain a key; this is done by gnuplot by default. This recipe will show you how to take complete control of your graph's legend.

How to do it…

Following is a gnuplot script showing the extra commands that produce the legend in the previous plot:

set term postscript landscape
set yrange [-1.5:1.5]
set xrange [0:6.3]
set ytics nomirror
set y2tics 0,.1
set y2range [0:1.2]
set style fill pattern 5
set key at graph .9, .9 spacing 3 font "Helvetica, 14"
set xlabel "Time (sec.) font "Courier, 12"
set ylabel "Amplitude" font "Courier, 12"
set y2label "Error Magnitude" font "Courier, 12"
set title "Fourier Approximation...