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

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parslee
parslee 2022-3-23
编辑： Matt J 2022-3-23
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

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Matt J
Matt J 2022-3-23
编辑：Matt J 2022-3-23
B = pagemtimes( reshape(A,128,257,[]) , reshape(y,257,1,[]) ) ;
B=squeeze(B);
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parslee
parslee 2022-3-23
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
Matt J 2022-3-23
编辑：Matt J 2022-3-23
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.

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