3-Matrix Algebra(上)

1.pdf

import numpy as np

# Creates an array of 4 x 4 with the main diagonal of 1

arr1 = np.eye(4)
print(arr1)
#[[1. 0. 0. 0.]
# [0. 1. 0. 0.]
# [0. 0. 1. 0.]
# [0. 0. 0. 1.]]

# or you can change the diagonal position

arr2 = np.eye(4, k=1)  # or try with another number like k= -2
print(arr2)

#[[0. 1. 0. 0.]
# [0. 0. 1. 0.]
# [0. 0. 0. 1.]
# [0. 0. 0. 0.]]

# but you can't change the diagonal in identity

arr3 = np.identity(4)
print(arr3)

#[[1. 0. 0. 0.]
# [0. 1. 0. 0.]
# [0. 0. 1. 0.]
# [0. 0. 0. 1.]]

2.pdf

3.pdf

4.pdf

a = np.array([[1, 2], [3, 4]])

print(a)

# [[1 2]
#  [3 4]]

a_t = a.transpose()
a.T

print(a_t)

# [[1 3]
#  [2 4]]

print(a_t.transpose())
# [[1 2]
#  [3 4]]

5.pdf

a = np.array([[1, 2], [3, 4]])
a_inv = np.linalg.inv(a)