a = np.arange(1,10).reshape(3,3)
b = np.arange(21,30).reshape(3,3)
np.einsum('ii->i',a)
------------...array([1, 5, 9])
np.einsum('ji',a)
------------
array([[1, 4, 7],
[2, 5, 8],
[3, 6, 9...]])
np.einsum('ij,jk',a,b)
------------
array([[150, 156, 162],
[366, 381, 396],