How to Use Ones in MATLAB: Syntax and Examples

In MATLAB, use the ones function to create an array filled with ones. You specify the size as input, like ones(3,4) for a 3-by-4 matrix of ones.

Syntax

The ones function creates an array of ones with specified dimensions.

• ones(n): creates an n-by-n square matrix of ones.
• ones(m,n): creates an m-by-n matrix of ones.
• ones([m,n,p,...]): creates an array with multiple dimensions.
• ones(..., 'datatype'): creates an array of ones with the specified data type, like 'double' or 'single'.

matlab

A = ones(3,4)
B = ones([2,3,2])
C = ones(5, 'single')

Output

A =
     1     1     1     1
     1     1     1     1
     1     1     1     1

B(:,:,1) =
     1     1     1
     1     1     1

B(:,:,2) =
     1     1     1
     1     1     1

C =
  single
     1     1     1     1     1

Example

This example shows how to create a 3-by-3 matrix of ones and use it to add to another matrix.

matlab

M = [2 3 4; 5 6 7; 8 9 10];
O = ones(3,3);
Result = M + O

Output

Result =
     3     4     5
     6     7     8
     9    10    11

Common Pitfalls

One common mistake is forgetting that ones(n) creates a square matrix, not a vector. Also, specifying dimensions incorrectly can cause errors.

For example, ones(3,4,5) creates a 3-by-4-by-5 array, which might be unexpected if you want a 2D matrix.

matlab

Wrong: V = ones(3); % creates 3x3 matrix, not a vector
Right: V = ones(1,3); % creates 1x3 row vector

Output

V =
     1     1     1
     1     1     1
     1     1     1

V =
     1     1     1

Quick Reference

Usage	Description
ones(n)	Create n-by-n matrix of ones
ones(m,n)	Create m-by-n matrix of ones
ones([m,n,p])	Create multi-dimensional array of ones
ones(..., 'datatype')	Create array with specified data type

Key Takeaways

Use ones(m,n) to create an m-by-n matrix filled with ones.

Specify dimensions as separate arguments or as a vector for multi-dimensional arrays.

Remember ones(n) creates a square matrix, not a vector.

You can specify the data type of the array with an optional argument.

Use ones to initialize arrays for calculations or placeholders.