# Objects that are bigger than others inside a matrix

I wonder, if possible, how to create a matrix that looks like this:

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Here's a solution without TikZ

\documentclass{article}
\usepackage{amssymb,array,arydshln}

\begin{document}
$\renewcommand{\arraystretch}{1.2} \left(\begin{array}{@{}c;{3pt/1.5pt}c@{}} \mathit{GL}(2,\mathbb{R}) & \begin{array}{@{}c@{}}*\\{}*\end{array}\\ \hdashline[3pt/1.5pt] \begin{array}{@{}c@{\hspace{1.5em}}c@{}}0&0\end{array} & * \end{array}\right)$
\end{document}


However I'm usually satisfied with solid lines for partitioned matrices, so

$\renewcommand{\arraystretch}{1.2} \left(\begin{array}{@{}c|c@{}} \mathit{GL}(2,\mathbb{R}) & \begin{array}{@{}c@{}}*\\{}*\end{array}\\ \hline \begin{array}{@{}c@{\hspace{1.5em}}c@{}}0&0\end{array} & * \end{array}\right)$


might be sufficient.

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Here's a possible solution using a matrix of math nodes from TikZ:

\documentclass{report}
\usepackage{amsmath}
\usepackage{amssymb}
\usepackage{tikz}
\usetikzlibrary{matrix}

\begin{document}

\begin{tikzpicture}[every left delimiter/.style={xshift=1ex}, every right delimiter/.style={xshift=-1ex}]
\matrix[matrix of math nodes,left delimiter=( , right delimiter=)] (mat)
{
\phantom{0} &[0.8cm] \phantom{0} & \ast \\
\phantom{0} & \phantom{0} & \ast \$0.3ex] 0 & 0 & \ast\\ }; \node[xshift=0.5cm,yshift=-7pt] at (mat-1-1) {GL(2,\mathbb{R})}; \draw[dashed,thick] (mat-1-2.north east) -- (mat-3-2.south east) ; \draw[dashed,thick] (mat-2-1.south west) -- (mat-2-3.south east) ; \end{tikzpicture} \end{document}  EDIT: and a more conventional approach, using the multirow and arydshln packages: \documentclass{report} \usepackage{amsmath} \usepackage{amssymb} \usepackage{multirow} \usepackage{arydshln} \begin{document} \[ \left( \begin{array}{cc:c} \multicolumn{2}{c:}{\multirow{2}{*}{GL(2,\mathbb{R})}} & \ast \\ & & \ast \\ \hdashline 0 & 0 & \ast \\ \end{array} \right)$

\end{document}


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