
a = np.zeros((5,5), dtype = np.int8)
np.fill_diagonal(a, 1)
print(a)

[[1 0 0 0 0]
 [0 1 0 0 0]
 [0 0 1 0 0]
 [0 0 0 1 0]
 [0 0 0 0 1]]


np.diag(np.full(5,1,np.int8))

array([[1, 0, 0, 0, 0],
       [0, 1, 0, 0, 0],
       [0, 0, 1, 0, 0],
       [0, 0, 0, 1, 0],
       [0, 0, 0, 0, 1]], dtype=int8)


a = np.zeros((3, 3), np.int8);
np.fill_diagonal(np.fliplr(a), [1,2,3])  # Horizontal flip
print(a)
np.fill_diagonal(np.flipud(a), [1,2,3]) # Vertical flip
print(a)
np.fill_diagonal(a, [1,2,3])
print(a)

[[0 0 1]
 [0 2 0]
 [3 0 0]]
[[0 0 3]
 [0 2 0]
 [1 0 0]]
[[1 0 3]
 [0 2 0]
 [1 0 3]]


a = np.zeros((5,5), dtype = np.int8)
np.fill_diagonal(np.flipud(a), np.full(5,1,np.int8))
print(a)

[[0 0 0 0 1]
 [0 0 0 1 0]
 [0 0 1 0 0]
 [0 1 0 0 0]
 [1 0 0 0 0]]

a

array([[0, 0, 0, 0, 1],
       [0, 0, 0, 1, 0],
       [0, 0, 1, 0, 0],
       [0, 1, 0, 0, 0],
       [1, 0, 0, 0, 0]], dtype=int8)

Diagonals¶