Matlab: Argmax and dot product for each row in a matrix

Question

I have 2 matrices = X in R^(n*m) and W in R^(k*m) where k<. Let x_i be the i-th row of X and w_j be the

Answer 1

Dot product is essentially matrix multiplication:

[~, Y] = max(W*X');

Answer 2

bsxfun based approach to speed-up things for you -

[~,Y] = max(sum(bsxfun(@times,X,permute(W,[3 2 1])),2),[],3)

On my system, using your dataset I am getting a 100x+ speedup with this.

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One can think of two more "closeby" approaches, but they don't seem to give any huge improvement over the earlier one -

[~,Y] = max(squeeze(sum(bsxfun(@times,X,permute(W,[3 2 1])),2)),[],2)

and

[~,Y] = max(squeeze(sum(bsxfun(@times,X',permute(W,[2 3 1]))))')