Let $X \in \text{Random}(\mathbb{R}^{N \times 1})$ be a D5210: Random real column matrix such that
Let $a \in \mathbb{R}^{N \times 1}$ be a D5200: Real column matrix.
(i) | \begin{equation} \mathbb{E} \Vert X \Vert^2_2 < \infty \end{equation} |
Then
\begin{equation}
\mathbb{E} \Vert X - \mathbb{E} X \Vert^2_2
= \mathbb{E} \Vert X - a \Vert^2_2 - \Vert \mathbb{E} X - a \Vert^2_2
\end{equation}