Matlab
Plotting  Horizontal Lines and Vertical
lines1. Basics
2. Code
3. Applied Example
4. Video (alternative code)
1. BasicsWe are going to create a simple Matlab function to add horizontal lines
(and
vertical ones) to any given Matlabcreated plot.
For
example, let's say that we need to add some indications or annotations
to a plot, and we need to display and indicate some upper or lower
limits.
The proposed Matlab function will have 5 input parameters:
 Initial value (where the horizontal line will
start)
 Final value (where the line will end)
 Y value (vertical position of the line with
respect to the plot)
 Direction (to indicate the direction of the
annotation: 1 going upwards, or 1 going downwards, like an
arrow)
 Vertical range (to display aesthetically
proportioned lines)
We plan the usage of our function like this (its name will be
'plot_limit'):
Usage: L = [L_min L_max y d r];
plot_limit(L);
where
L_min = starting point
L_max = ending point
y = y value of horizontal line
d = direction (1 or 1)
r = y range
So, we need to know in advance where we want to put our line
(sure!).
We
define our horizontal and vertical values. We arbitrarily define 300
horizontal points and use a linewidth = 1.5. The instruction 'hold on'
keeps the current figure, instead of overwriting it. This Matlab code
displays just a horizontal line.
a =
linspace(L_min, L_max, 300);
b =
linspace(y, y, 300);
plot(a,b,'k','linewidth',1.5)
hold on
Then, we
add some tiny vertical lines on each side of the horizontal one. If
direction 'd' is 1, the vertical lines are below the horizontal line
(going 'up'). If direction 'd' is 1, the vertical lines are above the
horizontal one (going 'down'). We take the vertical range into
account, in 'r', to display a vertical line of just 3% of the total
'height' of the current figure. You can try different values to suit
your needs, obviously. We find the initial or final points of the
vertical lines with an 'ifstatement'.
2. Code
This is the code to achieve it.
%
Initial
vertical line
a =
linspace(L_min, L_min, 10);
if d == 1
b = linspace(yr*.03, y, 10);
else
b = linspace(y, y+r*.03, 10);
end
plot(a,b,'k','linewidth',1.5)
hold on
%
Final
vertical line
a =
linspace(L_max, L_max, 10);
if d == 1
b = linspace(yr*.03, y, 10);
else
b = linspace(y, y+r*.03, 10);
end
plot(a,b,'k','linewidth',1.5)
3. Applied ExampleNow, we'll test our function with this script.
clear;
clc; close all
x = 0 :
2*pi/360 : 2*pi;
y =
sin(x);
plot(x,y)
grid on
xlabel('angle')
ylabel('sin(x)')
title('Plot
showing horizontal and vertical lines')
hold on
plot_limit([0.8,
2.5, 0.4, 1, 2])
plot_limit([4,
5.4, 0.6, 1, 2])
The result is:
The first line starts at 0.8, ends at 2.5, and has a vertical value of
0.4. The vertical lines simulate an uparrow (d = 1).
The second line starts at 4, ends at 5.4, and has a vertical value of
0.6. Direction goes down (d = 1).
4. Video
From
'Horizontal Lines' to home
From
'Horizontal Lines' to 2D plots

