How to check if a matrix is a square matrix in Numpy?

In this tutorial, we will look at how to check if a numpy matrix (a 2d numpy array) is a square matrix or not with the help of some examples.

What is a square matrix?

A matrix is said to be a square matrix if the number of rows is equal to the number of columns in the matrix. The following image shows a square matrix and a non-square matrix.

You can see that the number of rows and columns in a square matrix is the same, hence the name square.

How to check if a matrix is a square matrix in Numpy?

To check if a matrix is a square matrix or not, use the numpy.ndarray.shape property. For a 2d array, the .shape property returns a (m, n) tuple where m is the number of rows and n is the number of columns. To check if the matrix is square or not, simply check if m is equal to n or not.

The following is the syntax –

import numpy as np

# check if the matrix ar is square
len(ar.shape) == 2 and ar.shape[0] == ar.shape[1]

In the above syntax, we’re basically checking if the array is a 2d array with the same number of rows and columns.

Let’s now look at some examples of using the above syntax –

Example

Let’s create a square matrix and check if the above method identifies it correctly or not.

import numpy as np

# create a square matrix
ar = np.array([
    [1, 2],
    [3, 4]
])

# check if the matrix ar is square
print(len(ar.shape) == 2 and ar.shape[0] == ar.shape[1])

Output:

True

Here, we created a 2×2 square matrix and used the above method. We get True as the output indicating the array ar is a square matrix.

Let’s look at an example where the matrix is not a square matrix.

import numpy as np

# create a matrix
ar = np.array([
    [1, 2, 3],
    [4, 5, 6]
])

# check if the matrix ar is square
print(len(ar.shape) == 2 and ar.shape[0] == ar.shape[1])

Output:

False

Here, we applied the method on a 2×3 matrix. We get False as the output which indicates that the matrix ar is not a square matrix.

Note that if you apply this method on a non-2d array, you’ll get False as the result.

import numpy as np

# create a matrix
ar = np.array([1, 2, 3, 4])

# check if the matrix ar is square
print(len(ar.shape) == 2 and ar.shape[0] == ar.shape[1])

Output:

False

You might also be interested in –

• How to check if a matrix is a diagonal matrix in Numpy?
• Numpy – Check if Matrix is a Lower Triangular Matrix
• Numpy – Check if Matrix is an Upper Triangular Matrix