\begin{equation*} %\label{XYZ} \mathbf{A} = \begin{pmatrix} a_{11} &\dots &a_{1n}\\ \vdots &&\vdots\\ a_{m1} &\dots &a_{mn} \end{pmatrix} \end{equation*} | \begin{equation*} %\label{XYZ} \mathbf{B} = \begin{pmatrix} b_{11} &\dots &b_{1n}\\ \vdots &&\vdots\\ b_{m1} &\dots &b_{mn} \end{pmatrix}, \end{equation*} |