\begin{equation}		      		
M = \begin{pmatrix}
n_{1,1} & n_{1,2} & \cdots & n_{1,T} \\
\vdots & \vdots & \ddots & \vdots \\
n_{S,1} & n_{S,2} & \cdots & n_{S,T}
\end{pmatrix},
\label{eq:DATAMD2D}
\end{equation}
