import numpy as np

A = np.eye(3)
print(A)

B1 = np.fliplr(A)
print(B1)

B2 = A[:,::-1]
print(B2)

import numpy as np

b = [1, 2, 3]
B = np.diag(b)
print(B)
# [[1 0 0]
# [0 2 0]
# [0 0 3]]

B3 = np.rot90(B)
print(B3)
# [[0 0 3]
# [0 2 0]
# [1 0 0]]

B4 = np.flipud(B)
print(B4)

[[1 2 3]
 [4 5 6]
 [7 8 9]]
 
 ==>
 
 [2. 3. 6.]

import numpy as np

row = 3
A = np.arange(row**2)+1
A = np.mat(A.reshape([row, row]))
# print(A)

def ReduceData(R_xx, row):
  '''
  取上三角元素
  '''
  vector = []
  for i in range(0, row):
    a = R_xx[i, i + 1:]
    vector = np.append(vector, a)

  return vector

print(ReduceData(A, row))

[[1 2 3]
 [4 5 6]
 [7 8 9]]

==>

[3 5 7]

def DiagData(R_xx, row):
  '''
  取反对角线元素
  '''
  # vector = []
  vector = np.rot90(R_xx)
  vector = np.diag(vector)

  return vector


print(DiagData(A, row))