Multiply a 3D matrix with a 2D matrix

Question

Suppose I have an AxBxC matrix X and a BxD matrix Y.

Is there a non-loop method by which I can multiply

Answer 1

I would think recursion, but that's the only other non- loop method you can do

Answer 2

You could "unroll" the loop, ie write out all the multiplications sequentially that would occur in the loop

Answer 3

As a personal preference, I like my code to be as succinct and readable as possible.

Here's what I would have done, though it doesn't meet your 'no-loops' requirement:

for m = 1:C

    Z(:,:,m) = X(:,:,m)*Y;

end

This results in an A x D x C matrix Z.

And of course, you can always pre-allocate Z to speed things up by using Z = zeros(A,D,C);.

Answer 4

Nope. There are several ways, but it always comes out in a loop, direct or indirect.

Just to please my curiosity, why would you want that anyway ?