Multiplying a 2-D array to a specific dimension of a 3-D matrix

Question

Comrun Yousefzadeh 2020-6-17

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评论： Ameer Hamza 2020-6-18

Hello. I'm trying to multiply a two dimentioanl array to a specific dimension of a 3-D matrix. For example, A=[2000*2000*72], B=[72*3] and I'm trying to reach

C=[2000*2000*3]. In other words B should be multiplied to the 3rd dimension of A and repeated (element wise) for 2000*2000 points in the first two dimensions. Currently I'm using a loop like this:

for ii=1:size(A,1)
    for jj=1:size(A,2)
        A1=A(ii,jj,:);
        A1=A1(:);
        C1=B'*A1;  % C1 has dimension of 3*1
        C2=D*C1; %D is a 3-3 matrix therefore, C2 has the same dimension as C1
C(ii,jj,:)=C2(:,1);
    end
end

Is there a simple way to write this? I would rather avoid complications using "for loop".

Thanks, Cameron

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Answer 1

Ameer Hamza 2020-6-18

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https://ww2.mathworks.cn/matlabcentral/answers/550251-multiplying-a-2-d-array-to-a-specific-dimension-of-a-3-d-matrix#answer_452919

编辑：Ameer Hamza 2020-6-18

在 MATLAB Online 中打开

Try something like this

A = rand(100, 100, 72);
B = rand(72, 3);
A_C = mat2cell(A, ones(size(A,1),1), ones(size(A,2),1), size(A,3));
C = cell2mat(cellfun(@(x) {reshape(squeeze(x).'*B, 1, 1, [])}, A_C));

Although I guess that the solution using for-loop will be much faster.