normal equation

Normal Equation : Vector derivative 를 이용한 유도

Normal Equation : Vector derivative 를 이용한 유도OLS (Ordinal Least Square)에서 approximation of solution $\hat{\textbf{x}}$는 다음을 만족해야 함.$$\begin{aligned}\hat{\textbf{x}} &= \text{arg } \underset{\text{x}}{\text{min}} \Vert \textbf{b}-A\textbf{x} \Vert\\&=\text{arg } \underset{\text{x}}{\text{min} } \Vert \textbf{b}-A\textbf{x} \Vert ^2\\&=\text{arg } \underset{\text{x}}{\text{min} } (\textbf{b}-A\text..