6. Two axes and a model

The residual (log) and the drag coefficient (linear) on one plot: each needs its own scale. The second y axis, on the right, gives it — and a model function lies over the data.

set logscale y
set ylabel 'continuity residual'
set y2label 'cd'
set ytics nomirror
set y2tics

plot 'run.dat' using 1:2 title 'continuity', \
     ''        using 1:5 axes x1y2 with points pt 7 ps 0.6 title 'cd', \
     0.30 + 0.25*exp(-x/25)*cos(x/6) axes x1y2 dt 2 title 'model'

wheel: zoom · drag: pan · right drag: box · a resetopen page ↗

• axes x1y2 plots an item against the second y axis, autoscaled on its items alone.
• As in gnuplot, the y2 ticks are off until set y2tics; set ytics nomirror keeps the y ticks off the right border. set y2label, set y2range, set logscale y2 and set format y2 work as for y.
• An item that is not a quoted file is a function of x, with the operators of using expressions. It is sampled at set samples points (100) over the x range of the data — here the iterations, 1 to 120 — and titled as written. Functions are drawn with lines unless with or set style function say otherwise.

What you learned

A second y axis and model functions over data. Reference: gnuplot Subset, Functions.

Next: 7. A dashboard.