Matrix Algebra

[@yojiyamamoto3618]

Thank you for this great video. I've never seen such an explanation about dot product. I have questions and comment about it. 1. Is this why you said "moment condition means that covariance is roughly zero" in GMM video ? 2. (small matter) the representation of matrix multiplication in 19:30 might be the other way round (the left matrix and the right matrix), so the second line might be Σxi1xi1. and mean is \bar{x_{i1}}?

[@mronkko]

1) I do not understand the first question. Can you be more specific? 2) I do not understand the second comment either. What specifically do you think is not correct. A line of a matrix is a vector but you suggest that it would have a scalar value. The cell [2,1] would be Sigma x_2i x_1i.