\documentclass[12pt,a4paper]{report}
\input{commands} 
\usepackage{mathtools}
\usepackage{xepersian}
\usepackage{amsthm,amsmath}
\settextfont{XB Niloofar}
\begin{document}
\[ 
\mathbf{A_{n}}= {\left(\ \begin{matrix}
1& \ldots&n\\
2 & \ldots& n-1\\
\vdots & \udots & \vdots\\
n&\ldots&0\\
\end{matrix} \right)}
\]
\end{document}