3D Array Multiplication with 2D Matrix

Question

Anum Ahmed 2019-8-28

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回答： stav marzuk 2021-12-7

Hi,

I have a 3D array of lets say 500:10:32 elements. I want to multiple the first dimension of lthis array with another 1:500 matrix. How would I do this?

Regards

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Bob Thompson 2019-8-28

Which 500 elements from the first matrix do you want to multiply the second matrix by? There are 320 different options.

Or are you looking to multiply all 320 sets of 500 against the new matrix?

Also, how are you looking to store your new 500 x 500 matrices?

Anum Ahmed 2019-8-28

I am trying to perform the element wise multiplication of the 3D array with a second 2D array and getting the 3D array as a result where lets say row elements would be multiplied with another matrix.

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Answer 1

KALYAN ACHARJYA 2019-8-28

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编辑：KALYAN ACHARJYA 2019-8-28

在 MATLAB Online 中打开

data1=rand(500,10,32);% 3D Array
data2=rand(1,500);    %1x500 mat 
result=data1(1:500,1,1)*data2;  %Multiplication

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KALYAN ACHARJYA 2019-8-28

Yes @Bob Thanks

Bob Thompson 2019-8-28

Also, if you want to perform the multiplication on the entire 3D array, then the first thing that comes to mind for me is for loops, or arrayfun. There might be a way to do it without loops, but I don't know it (which doesn't say much).

for i = 1:size(data1,2)
    for j = 1:size(data1,3)
        data1(:,i,j) = data1(:,i,j).*data2';
    end
end

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Answer 2

Bruno Luong 2019-8-28

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https://ww2.mathworks.cn/matlabcentral/answers/477896-3d-array-multiplication-with-2d-matrix#answer_389421

编辑：Bruno Luong 2019-8-28

在 MATLAB Online 中打开

Simply do (R2016b or later)

data1 = data1 .* data2(:)

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Bob Thompson 2019-8-28

编辑：Bob Thompson 2019-8-28

Does this automatically choose the appropriate dimension though? I would logically make the connection between 500 and 500 elements in a dimension, but that doesn't mean a computer will.

Or will it produce 500 500x10x32 arrays, one for each element of data2?