Iterative parametric plot with gnuplot

Question

I want to use the iterative plot function plot for in gnuplot for a parametric plot.

set parametric
f(x) = x
plot for [i=1:2] t,f(i*t)

However, as I learned in this Question, the for iteration ends after a comma. So the iteration only applies to t and not to f(i*t). But since a parametric plot needs a pair of functions separated by a comma, how can I tell gnuplot to iteratively plot my parametric plot?

I don't know, but here on Version 5.0 patchlevel 3 it seems to work — bibi
– bibi, Commented May 4, 2016 at 12:27

Joce · Accepted Answer · 2016-05-04 14:51:09Z

2

Did you actually try it? gnuplot distinguishes a comma between parametric coordinates and the end of a plot-element as it is called (which can contain a for-loop): this is simply done by counting the number of coordinates given.

E.g.,

set parametric
set size ratio -1
plot for [i=1:3] cos(t),i*sin(t) title "Ellipse ".i, \
     for [i=1:3] i*cos(t),i*sin(t) title "Circle ".i

If you do

plot for [i=1:3] cos(t),i*sin(t),i*cos(t),i*sin(t)

then you keep the 3 ellipses (well, including the circle when i=1), and have one circle plotted for i=3 (the value i kept after the for loop) from the last pair of coordinates.

answered May 4, 2016 at 14:51

Joce

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2 Comments

thyme Over a year ago

Which gnuplot version do you use? I have gnuplot 4.6, and it seems not to work there.

Joce Over a year ago

I have gnuplot 5, but this also works with version 4.6 (patchlevel 6), it should work with versions >= 4.4. Please give detail on what "seems not to work". You should obtain 6 ellipses/circle in the first case (with ellipse 1 and circle 1 identical), 3 ellipses (1 being a circle) and 1 large circle (radius 3) in the second case.

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