access the main diagonal of an n-dimensional array.

See `diag_indices` for full details.

Parameters
----------
arr : array, at least 2-D

See Also
--------
diag_indices

Examples
--------
>>> import numpy as np

Create a 4 by 4 array.

>>> a = np.arange(16).reshape(4, 4)
>>> a
array([[ 0,  1,  2,  3],
       [ 4,  5,  6,  7],
       [ 8,  9, 10, 11],
       [12, 13, 14, 15]])

Get the indices of the diagonal elements.

>>> di = np.diag_indices_from(a)
>>> di
(array([0, 1, 2, 3]), array([0, 1, 2, 3]))

>>> a[di]
array([ 0,  5, 10, 15])

This is simply syntactic sugar for diag_indices.

>>> np.diag_indices(a.shape[0])
(array([0, 1, 2, 3]), array([0, 1, 2, 3]))

r