sum of product of 2 matrices

+1. What you don't seem to understand is that the * operator IS a dot product, i.e., the sum of products of elements. After all, MATLAB is a matrix language, so it is written to do these computations trivially, with the basic operators.

You sum of products is simply a dot product, what * delivers.

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Answer 2

Guillaume 2015-1-10

1
链接

此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/169480-sum-of-product-of-2-matrices#answer_164489

在 MATLAB Online 中打开

Use bsxfun:

sum(bsxfun(@times, u(c, :)', r))

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Zoltán Csáti 2015-1-10

Guillaume provided a vectorized version, that's why there is no matrix index j.

Guillaume 2015-1-10

在 MATLAB Online 中打开

bsxfun replicates u(c,:)' for each column j of r and sum calculates the sum for each of these columns. Exactly what you asked for.

Just try my code without any modification.

Note, this is equivalent to:

tempu = repmat(u(c, :)', 1, size(r, 2));
p = tempu .* r;
result = sum(p)

Or, if you really want to introduce j and make the calculation much slower:

tempu = repmat(u(c, :)', 1, size(r, 2));
p = tempu .* r;
result = zeros(1, size(r, 2));
for j = 1:size(r, 2)
   result(j) = sum(p(:, j));
end

The one line bsxfun does the same.

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