What is the colon notation in MATLAB?

Overview

MATLAB is a high-performance multi-paradigm programming language and numerical computing environment developed by MathWorks. MATLAB lets you work with matrices, display functions and data, implement algorithms, create user interfaces, and interact with programs written in other languages.

The symbol colon (:) is used as an operator in MATLAB programming and is a commonly used operator. This operator is used to construct a vector that is defined by a simple expression, iterate over or subscribe to an array, or access a set of elements of an existing vector.

Application of the MATLAB colon notation

Below are examples of some applications of the MATLAB colon notation.

Example 1

We can use the colon operator to create a vector with evenly spaced numbers where the colon operator uses default increment/decrement values.

Code 1

X = 1:10
// X = 1  2  3  4  5  6  7  8  9  10 

Code 2

X = 1:2:10
// X = 1  3  5  7  9  10 

Code 3

X = 100:-15:25
// X = 100  85  70  55  40  25

Example 2

Let’s say we have this statement 0:pi/9:pi. MATLAB will execute the statement and return the following result:

Code 4

0:pi/9:pi

// ans =

//  0.00000 0.34907 0.69813 1.04720 1.39626 1.74533 2.0944 2.44346 2.79253 3.14159

Explanation

This command will sequentially print the values that lie in the range of 0 to pi(3.14159). Also note that after every iteration, the value will be incremented by pi/9 = 0.34907 factor.

Check the following table for syntaxes to do this in a matrix B.

Code 5

Let’s create a script file and put the following code in it.

% The script file

B = [2 4 6 8; 10 12 14 16; 18 20 22 24]
B(:,1)      % display 1st column of B
B(:,2)      % display 2nd column of B
B(:,2:3)    % display 2nd and 3rd column of B
B(2:3,2:3)  % display 2nd and 3rd rows and 2nd and 3rd columns


//     B =  2    4    6    8
//          10   12   14   16
//          18   20   22   24

//   ans =  2
//          10
//          18

//   ans =  4
//          12
//          20

//   ans =  4    6
//          12   14
//          20   22

//   ans =  12   14
//          20   22

Explanation

In the above code:

• B=[2 4 6 8; 10 12 14 16; 18 20 22 24] : Creates a 3x4 size matrix B.
• B(:,1) : Displays the 1st column of matrix B.
• B(:,2) : Displays the 2nd column of matrix B.
• B(:,2:3) : Displays the 2nd and 3rd columns of matrix B.
• B(2:3,2:3) : Displays the rows (2nd and 3rd) and columns (2nd and 3rd) of matrix B.