python - Fast outer tensor product in numpy

Question

I have two numpy arrays:

x of shape ((d1,...,d_m)) 
y of shape ((e_1,...e_n)) 

I would like to form the outer tensor product, that is the numpy array

z of shape ((d1,...,d_m,e_1,...,e_n))

such that

z[i_1,...,i_n,i_{n+1}...,i_{m+n}] == x[i_1,...i_m]*y[i_{m+1},...,i_{m+n}]

I have to perform the above outer multiplication several times so I would like to speed this up as much as possible.

Answer 1

You want np.multiply.outer:

z = np.multiply.outer(x, y)