How to multiply a subset of matrix by a column from another matrix?

I have an array of 128x9252 and I would like to group them as

A1 = (:,1:257)

A2 = (:,258,514)

…

A36 = (:,8996:9252)

which will then be multiplied (.*) by y with the corresponding columns - y(:,1), y(:,2), y(:,3), etc.

This is what I want mathematically, A1 * y(:,1), A*y(:,2)), and so on.

How can I go about doing this?

This is what I have so far, but I keep getting an error saying 'Unable to perform assignment because the size of the left side is 128-by-1 and the size of the right side is 128-by-257.' and I'm not sure where the error is.

A = rand(128,9252);
B = zeros(128,257);
for m = 1:257
    for n = 1:36
        B(:,m) = A(:,257*(n-1)+1:257*n);
    end
end

Answer 1

[Matt J]

B = pagemtimes( reshape(A,128,257,[]) , reshape(y,257,1,[])  ) ;

B=squeeze(B);

[parslee]

I need the final matrix (B) to be the same size as A, but it's returning an array of 128x36.

[Matt J]

I need the final matrix (B) to be the same size as A, but it's returning an array of 128x36.

The operation you describe in your post should return that size. Each A_i * y(:,i) isa 128x1 vector and you have 36 of them.

[parslee]

Sorry, I didn't provide the correct information.

I want to multiply A1 = A(:,1:257), A2 = A(:,258:514), and so on by y = rand(1,257) and after multiplying A1.*y and A2.*y and so on, I want to concatenate them so that it returns to its original matrix size of 128x9252.

So this is what I did,

A = rand(128,9252);
y = rand(1,257);

A_reshape = reshape(A,128,257,[]);
B = A_reshape .* y;
B = reshape(B,128,9252);

Is the last line correct?

[Matt J]

That would just be,

B=reshape(A,128,257,[]).*y;

B=reshape(B,size(A));

You might, of course, want to consider keeping everything in 128x127x36 form throughout., rather than having to switch back and forth all the time.