and AB = BA. An example of AB = BA is when both A and B are identity matrices.
4. A row vector postmultiplied by a column vector is a scalar. Thus, consider the ordinary least-squares residuals u 1, u2,..., u„. Letting u be a column vector and u' be a row vector, we have uu uu = [U1 U2 U3
5. A column vector postmultiplied by a row vector is a matrix. As an example, consider the population disturbances of the classical linear regression model, namely, u1, u2,..., un. Letting u be a column vector and u' a row vector, we obtain rui u2
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