MATLAB: Column multiplication in the same matrix

matrix multiplicationvector

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

Best Answer

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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