matrix
在 內嵌套 a bmatrix
:
\documentclass{article}
\usepackage{amsmath}
\newcommand{\matr}[1]{\mathbf{#1}}
\begin{document}
\[
\matr{Z}_0=
\begin{bmatrix}
\begin{matrix}
\matr{A} & \matr{B} \\
\matr{X}_{tr} & \matr{X}_{tst} \\
\end{matrix}
\\
\matr{1}^T
\end{bmatrix}
\]
\end{document}