multiply element of a row vector (A) by corresponding row of matrix (B) and sum

Hi

I am currently looking for an assistance on the way to perform such calculation:

A=[0 1 2 3];B=[1 2;3 4;5 6;7 8];

        0*1 + 0*2
     C= 1*3 + 1*4
        2*5 + 2*6
        3*7 + 3*8

   ==> C=[0;7;22;45]

I had a look at

bsxfun(@times,,)

but it can't be useful here (unfortunately).

Best,

Answer 1

[Star Strider]

This works:

C = sum(bsxfun(@times, A', B),2);

To get bsxfun to work here, you have to transpose ‘A’ so that the two arguments have a dimension in common. Then sum across the columns (dimension 2).

[Isma]

Thanks a lot for the hint regarding the transpose of A. Cheers.

[Star Strider]

My pleasure.

Answer 2

[Matt J]

C=A(:).*sum(B,2);

[Isma]

Thanks a lot too. It's indeed interesting to know alternative solutions. Cheers.

[Matt J]

I had a look at bsxfun(@times,,) but it can't be useful here (unfortunately).

It's actually fortunate that you can avoid bsxfun. If B is an M x N matrix, then using bsxfun will require M*N multiplications, whereas with what I propose, you only do M multiplications.