Horizontal line in plot up to a graph

How can I generate a horizontal line starting at x = 0 up to a graph (see figure, red line)? The x, y coordinates are of course available for the graph.

Answer 1

[KSSV]

If you have the xlimits (x0,x1) and the y-value..the required equations is y = k.

x = 1:10 ;
k = 3 ;
y = k*ones(*Size(x)) ; 
plot(x,y)

Also have a look on line.

[Mepe]

I don't understand the code. How would you elegantly solve this with the line command? In such a way that it only runs to the graph?

Thanks!

[Mepe]

The value x1 should be freely chosen. From the point of intersection with the function (x, y) the line should run horizontally to x = 0.