CODEWITHSUNDEEP
pythonnumpydot-product
user3235916
user3235916

Reputation: 614

Numpy Dot Product of two 2-d arrays in numpy to get 3-d array

Sorry for the badly explained title. I am trying to parallelise a part of my code and got stuck on a dot product. I am looking for an efficient way of doing what the code below does, I'm sure there is a simple linear algebra solution but I'm very stuck:

puy = np.arange(8).reshape(2,4)
puy2 = np.arange(12).reshape(3,4)

print puy, '\n'
print puy2.T

zz = np.zeros([4,2,3])

for i in range(4):
    zz[i,:,:] = np.dot(np.array([puy[:,i]]).T,
                np.array([puy2.T[i,:]]))

Upvotes: 6

Views: 314

Answers (2)

Divakar
Divakar

Reputation: 221764

Here's another way with broadcasting -

(puy[None,...]*puy2[:,None,:]).T

Upvotes: 3

DSM
DSM

Reputation: 353604

One way would be to use np.einsum, which allows you to specify what you want to happen to the indices:

>>> np.einsum('ik,jk->kij', puy, puy2)
array([[[ 0,  0,  0],
        [ 0, 16, 32]],

       [[ 1,  5,  9],
        [ 5, 25, 45]],

       [[ 4, 12, 20],
        [12, 36, 60]],

       [[ 9, 21, 33],
        [21, 49, 77]]])
>>> np.allclose(np.einsum('ik,jk->kij', puy, puy2), zz)
True

Upvotes: 6

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