Line
Segment  equation of a straight line in Matlab
A line segment
is a straight line which links two points without extending beyond
them. In
this article we’re going to develop three functions to work out
equations of
straight lines in Matlab with different approaches.

At the end, we’re going to
wrap those three functions in a menu, so that the user can choose the
appropriate one, according to known data.
In
two
dimensions, the equation is often given by the slopeintercept form
y = mx
+ b
where: 
m is the slope of the line (y_{2} – y_{1})/(x_{2} – x_{1})
b is the yintercept
of the line
x is the independent variable of the function y = f(x)
Our first
function assumes you enter points (x1, y1) and
(x2, y2), and the function returns the slope m and the intersect b.
function [m, b]
= str_lin1(x1, y1, x2, y2)
m =
(y2y1) / (x2x1);
b = y1 
m*x1;
Now, the
following video shows you how to use the concepts of point and slope to
find linear equations. After the video, we show you how to implement a
function to easily achieve the equivalent results.
Our
second function in this task, assumes you enter point (x, y) and the
slope. It
returns the
intercept.
function b =
str_lin2(x1, y1, m)
b = y1 
m*x1;
The
third function interpolates an entered value. You enter the slope, the
intercept and the value. The function returns the interpolated values.
function [x, y]
= str_lin3(m, b, val)
y =
m*val + b;
x = (val
 b) / m;
Now, we’re going to wrap
those three functions using a menu
and a switch structure:
%
Functions on straight lines
clear all, clc,
format compact, close all
option =
menu('Choose
your case: y = mx + b',...
'Enter (x1, y1) and (x2,
y2); get
m and b',...
'Enter (x1, y1) and m; get
b',...
'Enter m, b and a value;
get
interpolated (val, y) and (x, val)');
switch option
case 1
x1 = input('Enter
x1 = ');
y1 = input('Enter
y1 = ');
x2 = input('Enter
x2 = ');
y2 = input('Enter
y2 = ');
[m, b] = str_lin1(x1, y1, x2, y2)
case 2
x1 = input('Enter
x1 = ');
y1 = input('Enter
y1 = ');
m = input('Enter
m = ');
b = str_lin2(x1, y1, m)
case 3
m = input('Enter
m = ');
b
= input('Enter
b = ');
v = input('Enter
val = ');
[x, y] = str_lin3(m, b, v);
str = ['(' num2str(v) ', '
num2str(y) ')'];
disp(str)
str = ['(' num2str(x) ', '
num2str(v) ')'];
disp(str)
end
Let’s assume that the
script above is called line_segment.
We can run some examples from the command window, like this...
>>line_segment
Example 1: enter two points
Matlab displays the
following menu:
If we click on the first option, the flow is like this:
Enter x1 = 0
Enter y1 = 2
Enter x2 = 2/3
Enter y2 = 0
and the results are
m =
3
b = 2
Example 2: enter one point and slope
Let's run again our code,
but this time we select the second button. The scirpt works like this...
Enter x1 = 2/3
Enter y1 = 0
Enter m = 3
and the result is
b = 2
Example 3: enter slope, intercept and one value
to be
interpolated
Finally, the third option
can be used for a simple linear interpolation. Let's run
it, and we get...
Enter m = 4
Enter b = 1
Enter val = 0
(0, 1)
(0.25, 0)
From
'Line Segment' to home
From 'Line Segment' to Flow Control
