Gnuplot - draw a vertical line from the x-axis to the plot, and from the plot to the y-axis

Question

I have a Gaussian curve drawn via gnuplot and I want to have a line which goes up from the x-axis, stops exactly where it hits the curve, and goes perpendicular to the left to hit the y-axis, ideally displaying the values at both axis, and displaying a symbol where it intersects with the x-axis.

What is the right way to add this in gnuplot? I tried to play around with arrows using nohead but I am a newbie to gnuplot and can't seem to find a way to achieve what I need.

Answer 1

I managed to find a simple solution to my needs. The arrow can actually be used with nohead by specifying the y coordinates of the to to be the function of the plot itself.

So lets say we have a function f(x), and we want to draw a line from x=3 to f(3) and the corresponding horizontal line y= f(3), all we have to do is add 2 arrows:

set arrow from 3,0 to 3,f(3) nohead
set arrow from 0,f(3) to 3,f(3) nohead

Since I also wanted tics to be added where the line intersects with the axis, if they're missing, one could then do:

set xtics add (3 3)
set ytics (f(3) f(3))

Since there might be decimal places involved on the y axis one might also need to do something like this (in this case it has 3 decimal places):

set format y "%1.3f"

I didn't manage to find a way to do a label underneath a tic on the x-axis, but the above sufficed for my needs. Hope it helps for someone else looking for the same solution.