Column multiplication in the same matrix

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Mahmoud Solomon 2018-3-29

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https://ww2.mathworks.cn/matlabcentral/answers/391469-column-multiplication-in-the-same-matrix

评论： Yuanli Guo 2021-12-13

I have a 3 by 3 matrix and would like to loop and multiply column 1 with all other columns but not itself and also column 2 with other columns but not itself and column 3 with other columns but not itself.

x11 = [1 2 3; 4 5 3; 2 8 3];

[m12, n12] = size(x11);

for i = 1:m12

    for j = 1:n12
         x1x1(i, j)=x11(i, j).*x11(i, j)
    end
end

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Star Strider 2018-3-29

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https://ww2.mathworks.cn/matlabcentral/answers/391469-column-multiplication-in-the-same-matrix#answer_312628

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Try this:

x11 = [1 2 3; 4 5 3; 2 8 3];
[m12, n12] = size(x11);
for k1 = 1:n12
    x11t = x11;                                             % Copy ‘x11’
    idx = setdiff(1:n12, k1)                                % Columns To Be Multiplied
    x11t(:,idx) = bsxfun(@times, x11(:,idx), x11(:,k1))     % Assign Multiplied ‘Columns To Be Multiplied’ To Appropriate Columns Of ‘x11t’
    x1x1(:,:,k1) = x11t;                                    % Store In Output Array
end

It appears to do what you want.

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Mahmoud Solomon 2018-4-3

Thanks again.

Star Strider 2018-4-3

As always, my pleasure.

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更多回答（2 个）

Elias Gule 2018-3-29

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https://ww2.mathworks.cn/matlabcentral/answers/391469-column-multiplication-in-the-same-matrix#answer_312629

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Here you go:

[nr,nc] = size(x11);
for col = 1 : nc
  col_data = x11(:,col);
  col_prod = bsxfun(@times,col_data,x11(:,~all(ismember(x11,col_data))));
  col_prod   % you can store this in another array
end

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Mahmoud Solomon 2018-3-29

Thanks for the respond but I am not getting the desire result. The resulting matrix should look like this [2 6 3; 20 15 12; 16 24 6]. Again, column 1 multiplies columns 2 and 3 and column 3 multiplies column 1.

Elias Gule 2018-3-29

在 MATLAB Online 中打开

ok. I see what you mean. You are basically multiplying the columns of a matrix while ignoring the currently selected column.

x11 = [1 2 3; 4 5 3; 2 8 3];
[nr,nc] = size(x11);
for col = 1 : nc
col_data = x11(:,col);
tempX11  = x11(:,~all(ismember(x11,col_data)));
col_prod = tempX11(:,1).*tempX11(:,2);
col_prod   % you can store this in another array
end

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Elias Gule 2018-3-29

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https://ww2.mathworks.cn/matlabcentral/answers/391469-column-multiplication-in-the-same-matrix#answer_312643

在 MATLAB Online 中打开

I believe this works as expected:

x11 = [1 2 3; 4 5 3; 2 8 3];
[nr,nc] = size(x11);
for col = 1 : nc
 col_data = x11(:,col);
 tempX11  = x11(:,~all(ismember(x11,col_data)));
 col_prod = tempX11(:,1).*tempX11(:,2);
 col_prod   % you can store this in another array
end