matrix-properties-of-numpy-arrays.py

import numpy as np

np.eye(3)
# array([[1., 0., 0.],
#        [0., 1., 0.],
#        [0., 0., 1.]])


mat = np.array([[1, 2], [3, 4]])
mat.transpose()
# array([[1, 3],
#        [2, 4]])
mat.T
# array([[1, 3],
#        [2, 4]])


A = np.array([[1, 2], [3, 4]])
A.trace()  # 5

A = np.array([[1, 2], [3, 4]])
B = np.array([[-1, 1], [0, 1]])
A @ B
# array([[-1, 3],
#        [-3, 7]])
A * B
# array([[-1, 2],
#        [ 0, 4]])


A = np.array([[1, 2], [3, 4]])
I = np.eye(2)
A @ I
# array([[1, 2],
#        [3, 4]])


from numpy import linalg
linalg.det(A)  # -2.0000000000000004
linalg.inv(A)
# array([[-2. , 1. ],
#        [ 1.5, -0.5]])


Ainv = linalg.inv(A)
Ainv @ A
# Approximately
# array([[1., 0.],
#       [0., 1.]])

A @ Ainv
# Approximately
# array([[1., 0.],
#        [0., 1.]])