CODEWITHSUNDEEP
numpypytorchnumpy-ndarray
Tony
Tony

Reputation: 1404

Multiply every row of a matrix with every row of another matrix

In numpy / PyTorch, I have two matrices, e.g. X=[[1,2],[3,4],[5,6]], Y=[[1,1],[2,2]]. I would like to dot product every row of X with every row of Y, and have the results

[[3, 6],[7, 14], [11,22]]

How do I achieve this?, Thanks!

Upvotes: 2

Views: 359

Answers (3)

Anubhav Singh
Anubhav Singh

Reputation: 8719

In PyTorch, you can achieve this using torch.mm(a, b) or torch.matmul(a, b), as shown below:

x = np.array([[1,2],[3,4],[5,6]])
y = np.array([[1,1],[2,2]])
x = torch.from_numpy(x)
y = torch.from_numpy(y)
# print(torch.matmul(x, torch.t(y)))
print(torch.mm(x, torch.t(y)))

output:

tensor([[ 3,  6],
        [ 7, 14],
        [11, 22]], dtype=torch.int32)

Upvotes: 1

user3483203
user3483203

Reputation: 51185

Using einsum

np.einsum('ij,kj->ik', X, Y)


array([[ 3,  6],
       [ 7, 14],
       [11, 22]])

Upvotes: 1

Sarim Aleem
Sarim Aleem

Reputation: 170

I think this is what you are looking for:

import numpy as np

x= [[1,2],[3,4],[5,6]] 
y= [[1,1],[2,2]]

x = np.asarray(x) #convert list to numpy array 
y = np.asarray(y) #convert list to numpy array

product = np.dot(x, y.T)

.T transposes the matrix, which is neccessary in this case for the multiplication (because of the way dot products are defined). print(product) will output:

[[ 3  6]
 [ 7 14]
 [11 22]]

Upvotes: 4

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