How to Use rand in MATLAB for Random Numbers

In MATLAB, use the rand function to generate random numbers between 0 and 1. You can call rand with size arguments like rand(m,n) to create an m-by-n matrix of random values.

Syntax

The rand function generates uniformly distributed random numbers between 0 and 1.

• r = rand: returns a single random number.
• r = rand(n): returns an n-by-n matrix of random numbers.
• r = rand(m,n): returns an m-by-n matrix of random numbers.
• r = rand([m n]): also returns an m-by-n matrix.

matlab

r = rand
r2 = rand(3)
r3 = rand(2,4)
r4 = rand([2 3])

Output

r = 0.8147
r2 =
    0.9058    0.1270    0.9134
    0.6324    0.2785    0.5469
    0.9575    0.9649    0.4218
r3 =
    0.7922    0.9595    0.6557    0.0357
    0.6555    0.0357    0.8491    0.9340
r4 =
    0.6787    0.7577    0.7431
    0.4387    0.7431    0.3922

Example

This example shows how to create a 4-by-5 matrix of random numbers and calculate the mean of all values.

matlab

A = rand(4,5);
meanValue = mean(A, 'all');
disp('Random matrix A:');
disp(A);
disp(['Mean of all elements: ' num2str(meanValue)]);

Output

Random matrix A:
    0.8147    0.9058    0.1270    0.9134    0.6324
    0.2785    0.5469    0.9575    0.9649    0.1576
    0.9706    0.9572    0.4854    0.8003    0.1419
    0.4218    0.9157    0.7922    0.9595    0.6557
Mean of all elements: 0.6643

Common Pitfalls

One common mistake is expecting rand to generate integers or numbers outside 0 to 1. rand only produces decimal numbers between 0 and 1.

To get random integers, use randi instead.

Another pitfall is forgetting to specify matrix size, which returns only one number.

matlab

wrong = rand(5); % This creates a 5x5 matrix, not integers
correct = randi([1,10],5,5); % This creates a 5x5 matrix of integers from 1 to 10

Output

wrong =
    0.8147    0.9058    0.1270    0.9134    0.6324
    0.2785    0.5469    0.9575    0.9649    0.1576
    0.9706    0.9572    0.4854    0.8003    0.1419
    0.4218    0.9157    0.7922    0.9595    0.6557
    0.6555    0.0357    0.8491    0.9340    0.6787

correct =
     9     3     7     6     2
     1     4     5     8     9
     2     7     1     3     4
     6     8     9     5     7
     3     1     2     4     6

Quick Reference

Usage	Description
rand	Single random number between 0 and 1
rand(n)	n-by-n matrix of random numbers
rand(m,n)	m-by-n matrix of random numbers
randi([a,b],m,n)	m-by-n matrix of random integers between a and b

Key Takeaways

Use rand to generate random decimal numbers between 0 and 1 in MATLAB.

Specify matrix size in rand(m,n) to get multiple random numbers.

rand does not generate integers; use randi for random integers.

rand([m n]) and rand(m,n) both create matrices of random numbers.

Always check the size of output to avoid unexpected single values.