Python | Numpy matrix.sum()

matrix.sum() is a NumPy function used to calculate the sum of all elements in a matrix. It can also compute row-wise and column-wise sums using the axis parameter. This method works only with NumPy matrix objects, not arrays.

Example:

Input: [[1, 2], [3, 4]]
Output: 10

Syntax

matrix.sum(axis=None)

Parameter: axis (Optional) -

• None: sum of all elements
• 0: column-wise sum
• 1: row-wise sum

Examples

Example 1: This example creates a 2×2 matrix using np.matrix and computes the sum of all its elements using matrix.sum().

import numpy as np
m = np.matrix([[4, 1],
              [12, 3]])
out = m.sum()
print(out)

20

Explanation: m.sum() adds all elements (4 + 1 + 12 + 3 = 20).

Example 2: This example calculates the sum of each row separately by setting axis=1.

import numpy as np

m = np.matrix([[4, 1, 9],
               [12, 3, 1],
               [4, 5, 6]])
out = m.sum(axis=1)
print(out)

[[14]
 [16]
 [15]]

Explanation: m.sum(axis=1) sums each row individually.

Example 3: This example finds the sum of each column in a 3×3 matrix using axis=0.

import numpy as np

m = np.matrix([[2, 4, 6],
               [1, 3, 5],
               [7, 8, 9]])
out = m.sum(axis=0)
print(out)

[[10 15 20]]

Explanation: m.sum(axis=0) sums column-wise (2+1+7), (4+3+8), (6+5+9)