{N\times (p+1)}\non
 \end{equation}\]</div>
<p>and </p>
<div class="arithmatex">\[\begin{equation}
    \bb{X}^T = \begin{pmatrix}
1 &amp; 1 &amp; \cdots &amp; 1 \\
x_{11} &amp; x_{21} &amp; \cdots &amp; x_{N1} \\
\vdots  &amp; \vdots  &amp; \ddots &amp; \vdots  \\
x_{1p} &amp; x_{2p} &amp; \cdots &amp; x_{Np} 
\end{pmatrix} = 
\begin{pmatrix}
    1 &amp; 1 &amp; \cdots &amp; 1\\
    x_1 &amp; x_2 &amp; \cdots &amp; x_N
\end{pmatrix}\in \mathbb{R}^{(p+1)\times N}.\non
\end{equation}\]</div>
<p>We have </p>
<