Can anybody explain me the numpy.indices()?

Question

Suppose you have a matrix M whose (i,j)-th element equals

M_ij = 2*i + 3*j

One way to define this matrix would be

i, j = np.indices((2,3))
M = 2*i + 3*j

which yields

array([[0, 3, 6],
       [2, 5, 8]])

In other words, np.indices returns arrays which can be used as indices. The elements in i indicate the row index:

In [12]: i
Out[12]: 
array([[0, 0, 0],
       [1, 1, 1]])

The elements in j indicate the column index:

In [13]: j
Out[13]: 
array([[0, 1, 2],
       [0, 1, 2]])