Calculate the sum of the diagonal elements of a NumPy array

Sometimes we need to find the sum of the Upper right, Upper left, Lower right, or lower left diagonal elements. Numpy provides us the facility to compute the sum of different diagonals elements using numpy.trace() and numpy.diagonal() method.

Method 1: Finding the sum of diagonal elements using numpy.trace()

Syntax : numpy.trace(a, offset=0, axis1=0, axis2=1, dtype=None, out=None)

Example 1: For 3X3 Numpy matrix

Python3

# importing Numpy package
import numpy as np

# creating a 3X3 Numpy matrix
n_array = np.array([[55, 25, 15],
                    [30, 44, 2],
                    [11, 45, 77]])

# Displaying the Matrix
print("Numpy Matrix is:")
print(n_array)

# calculating the Trace of a matrix
trace = np.trace(n_array)


print("\nTrace of given 3X3 matrix:")
print(trace)

Output:

Example 2: For 4X4 Numpy matrix

Python3

# importing Numpy package
import numpy as np

# creating a 4X4 Numpy matrix
n_array = np.array([[55, 25, 15, 41],
                    [30, 44, 2, 54],
                    [11, 45, 77, 11],
                    [11, 212, 4, 20]])

# Displaying the Matrix
print("Numpy Matrix is:")
print(n_array)

# calculating the Trace of a matrix
trace = np.trace(n_array)


print("\nTrace of given 4X4 matrix:")
print(trace)

Output:

Method 2: Finding the sum of diagonal elements using numpy.diagonal()

Syntax :

numpy.diagonal(a, offset=0, axis1=0, axis2=1

Example 1: For 3X3 Numpy Matrix

Python3

# importing Numpy package
import numpy as np

# creating a 3X3 Numpy matrix
n_array = np.array([[55, 25, 15],
                    [30, 44, 2],
                    [11, 45, 77]])

# Displaying the Matrix
print("Numpy Matrix is:")
print(n_array)

# Finding the diagonal elements of a matrix
diag = np.diagonal(n_array)

print("\nDiagonal elements are:")
print(diag)

print("\nSum of Diagonal elements is:")
print(sum(diag))

Output:

Example 2: For 5X5 Numpy Matrix

Python3

# importing Numpy package
import numpy as np

# creating a 5X5 Numpy matrix
n_array = np.array([[5, 2, 1, 4, 6],
                    [9, 4, 2, 5, 2],
                    [11, 5, 7, 3, 9],
                    [5, 6, 6, 7, 2],
                    [7, 5, 9, 3, 3]])

# Displaying the Matrix
print("Numpy Matrix is:")
print(n_array)

# Finding the diagonal elements of a matrix
diag = np.diagonal(n_array)

print("\nDiagonal elements are:")
print(diag)

print("\nSum of Diagonal elements is:")
print(sum(diag))

Output: