Numpy Broadcast to perform euclidean distance vectorized

Question

I have matrices that are 2 x 4 and 3 x 4. I want to find the euclidean distance across rows, and get a 2 x 3 matrix at the end. Here is the code with one for loop that compu

Answer 1

I had the same problem recently working with deep learning(stanford cs231n,Assignment1),but when I used

 np.sqrt((np.square(a[:,np.newaxis]-b).sum(axis=2)))

There was a error

MemoryError

That means I ran out of memory(In fact,that produced a array of 500*5000*1024 in the middle.It's so huge!)

To prevent that error,we can use a formula to simplify:

code:

import numpy as np
aSumSquare = np.sum(np.square(a),axis=1);
bSumSquare = np.sum(np.square(b),axis=1);
mul = np.dot(a,b.T);
dists = np.sqrt(aSumSquare[:,np.newaxis]+bSumSquare-2*mul)