gnuplot - plot horizontal line over shorter range than the axis

Meson · 07-29-2008, 10:20 PM

For example:

I am plotting a parabola.

I'd like to plot a horizontal line that spans from the left to right wall of the curve. I'd like the horizontal line to stop at each intersection, forming an upside-down 'A'

Is there an easy way to do this?

BrianK · 07-30-2008, 03:32 PM

of the curve? What curve? This sounds like homework.

Meson · 07-30-2008, 03:48 PM

Hah, no, it's not homework. I just used curve as a generic term. And a parabola for simplicity. I'm actually plotting electronic potential curves for diatomic molecules and the horizontal line is supposed to be the total energy.

Code:

set xrange [-5:5]

plot x**2 with lines lt 1 title "y = x^2", \
     4    with lines lt 1 title "y = 4, -2 <= x <= 2"

So for this I want to plot the parabola, but I only want the horizontal line to go from -2 to 2.

BrianK · 07-30-2008, 05:27 PM

ahh.. well, I suppose the answer relates to how much you want to do. Certainly you can draw a line between any two points on the screen, so if you don't mind figuring the intersection points externally, it would be pretty easy to plot from, say -2,4 to 2,4 and so on, but if you're looking for something like a "trim" function that trims a line at a given point, I don't know of one (which does not necessarily mean that it's not possible).

ne pas · 07-30-2008, 06:22 PM

Is this useful for you?

Code:

set xrange [-5:5]

plot x**2 title "y = x^2" with lines lt 1, \
     x**2 notitle with filledcurves below y1=4

kotzyba · 10-18-2008, 08:41 AM

Code:

set arrow 10 from -2,4 to 2,4 nohead

use this code before ploting
you can unset the arrow with

Code:

unset arrow 10

hope it helps