Numpy operation

Question

Given a nxn matrix, how can we find all possible combination of 3x3 matrix?

Answer 1

I like to use numpy.ix_ to extract submatrices.

import numpy as np
from itertools import combinations

n = 4
mat = np.arange(n**2).reshape((n, n))

print("Original matrix:\n", mat)
print("\n3x3 submatrices:")

for r in combinations(range(n), 3):
for c in combinations(range(n), 3):
print(mat[np.ix_(r, c)])
print()

Reference: https://docs.scipy.org/doc/numpy/reference/generated/numpy.ix_.html

Answer 2

4