How can I output this special matrix?

Question

I want to output a special matrix like this:

But, I don't know how to do this.

Thanks very much!

Answer 1

I propose three variant: in display style, medium size (with the \medmathcommand from nccmath – ca 80 % of display style) and supposedly text style with the psmallmatrix(*) defined by mathtools. Of course, with four rows, this will enlarge the line spacing locally.

\documentclass{article}
\usepackage{mathtools, nccmath}
\usepackage{array}

\begin{document}

\[ \setlength{\arraycolsep}{3pt}
A' = \begin{pmatrix}
 & & & & & & & 0\\
 \multicolumn{7}{c}{\raisebox{-1.5ex}{\smash{\huge$A$}}} & 0 \\[-1.5ex]
 & & & & & & & ⋮ \\
 0 & 0 & \hdotsfor{5} &0
\end{pmatrix}
\] 

\[ \setlength{\arraycolsep}{2pt}
A' = \medmath{\begin{pmatrix}
 & & & & & & & 0\\
 \multicolumn{7}{c}{\raisebox{-1.5ex}{\smash{\Large$A$}}} & 0 \\[-1.5ex]
 & & & & & & & ⋮ \\[-0.5ex]
 0 & 0 & \hdotsfor{5} \!&0
\end{pmatrix}}
\]

Some text. Some more text. An in-text matrix $ A' = \begin{psmallmatrix}
 & & & & 0\\[0.5ex]
 \multicolumn{4}{c}{\raisebox{-1.5ex}{\smash{\large$A$}}} & 0 \\[-2.3ex]
 & & & & \vdots \\[0.4ex]
 0 & 0 & \!\hdots\! &\! \hdots\! & 0
\end{psmallmatrix}$
\end{document}