In matrix notation what does it mean X 'X I see it in this academic paper, I can't find it in matrix operation and can't search with google.
page 7 , paragraph 3.1
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$\begingroup$$X'$ is the transpose matrix and $X'X$ is the product the same matrix. exemple $$X=\left(\matrix{1 & 2&4\\1&3&5}\right),$$ then, $$X'X=\left(\matrix{1 & 1\\2&3\\4&5}\right)\left(\matrix{1 & 2&4\\1&3&5}\right).$$
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