Boxed entries in matrices

I would like to create a formula or figure like this:

I tried it simply with the pmatrix environment and the \boxed command, but the spacing looked horrible. I think it might be done with TikZ, but I don't know much about it.

Edit:

Here is what I got so far for the right-hand side:

\documentclass{article}

\usepackage{amsmath,amsthm,amsfonts,amssymb}
\usepackage{tikz}
\usetikzlibrary{arrows,matrix,positioning}

\begin{document}
\begin{tikzpicture}
\matrix [matrix of math nodes,left delimiter=(,right delimiter=)] (m)
{
A_1           & \phantom{A_1} & \phantom{A_1} & \\
\phantom{A_1} & \phantom{A_1} &               & \\
\phantom{A_1} &               & A_2           & \\
&               &               & A_2           & \phantom{A_3}\\
&               &               & \phantom{A_2} & A_3          \\
};
\draw (m-1-1.north west) -- (m-1-2.north east) -- (m-2-2.south east) -- (m-2-1.south west) -- (m-1-1.north west);
\draw (m-3-3.north west) -- (m-3-3.north east) -- (m-3-3.south east) -- (m-3-3.south west) -- (m-3-3.north west);
\draw (m-4-4.north west) -- (m-4-4.north east) -- (m-4-4.south east) -- (m-4-4.south west) -- (m-4-4.north west);
\draw (m-1-1.north west) -- (m-1-3.north east) -- (m-3-3.south east) -- (m-3-1.south west) -- (m-1-1.north west);
\draw (m-5-5.north west) -- (m-5-5.north east) -- (m-5-5.south east) -- (m-5-5.south west) -- (m-5-5.north west);
\draw (m-4-4.north west) -- (m-4-5.north east) -- (m-5-5.south east) -- (m-5-4.south west) -- (m-4-4.north west);
\end{tikzpicture}

\end{document}


What I hope to achieve is

• square boxes,
• $A_1$ centered in the $2\times 2$ box,
• also the left-hand side and the $\subset$ sign in the middle.

Comment: I have no idea what I did wrong in the formatting of this question.

-
–  Werner Apr 3 '13 at 19:59
do you also have an idea how to center $A_1$ in a $2\times 2$ matrix? –  Peter Patzt Apr 3 '13 at 20:05
Yes, see Combine 4 cells in a table where you can use a combination of \multicolumn and \multirow. –  Werner Apr 3 '13 at 20:12
Welcome to TeX.sx! –  Peter Jansson Apr 3 '13 at 20:16
are you sure, that \multirow works in tikz? It throws Error: Undefined control sequence. @Peter Jansson: sorry for the discussion, but I'd like to make it work. –  Peter Patzt Apr 3 '13 at 20:22

A TikZ solution:

\documentclass{article}
\usepackage{amsmath,tikz}
\usetikzlibrary{matrix}

\begin{document}
$\begin{tikzpicture}[baseline=(current bounding box.center)]% \matrix[matrix of math nodes, inner sep=0, nodes={draw,outer sep=0,inner sep=2pt}, every left delimiter/.style={xshift=1ex},%tighter delimiter spacing every right delimiter/.style={xshift=-1ex}, left delimiter={(},right delimiter={)}, column sep=-\pgflinewidth,row sep=-\pgflinewidth] (r) { |[inner sep=5mm]|A_1&&\\ &A_2&\\ &&A_3\\ }; \end{tikzpicture} \subset \begin{tikzpicture}[baseline=(current bounding box.center)]% \matrix[matrix of math nodes, inner sep=0, nodes={draw,outer sep=0,inner sep=2pt}, every left delimiter/.style={xshift=1ex},%tighter delimiter spacing every right delimiter/.style={xshift=-1ex}, left delimiter={(},right delimiter={)}, column sep=-\pgflinewidth,row sep=-\pgflinewidth] (l) { |[inner sep=5mm]|A_1&&&\\ &A_2&&\\ &&A_2&\\ &&&A_3\\ }; \draw (l-2-2.north east) |- (l-1-1.north east) (l-2-2.south west) -| (l-1-1.south west) (l-3-3.north east) -| (l-4-4.north east) (l-3-3.south west) |- (l-4-4.south west); \end{tikzpicture}$
\end{document}


-
WOW ... that looks awesome! Thanks a lot! –  Peter Patzt Apr 3 '13 at 20:54
@PeterPatzt My pleasure –  percusse Apr 3 '13 at 20:56

A TikZ-free solution, using the easybmat package:

\documentclass{article}
\usepackage{amsmath}
\usepackage{easybmat}

\begin{document}

$\left( \begin{array}{c@{}c@{}c} \begin{BMAT}{|ccc|}{|ccc|} & & \\ & \mbox{\LARGEA_1} & \\ & & \end{BMAT} & & \\ & \begin{BMAT}{|c|}{|c|} A_2 \end{BMAT} & \\ & & \begin{BMAT}{|c|}{|c|} A_3 \end{BMAT} \end{array} \right) \subset \left( \begin{array}{c@{}c@{}c} \begin{BMAT}{|ccc|c|}{|ccc|c|} & & & \\ & \mbox{\LARGEA_1} & & \\ & & & \\ & & & A_2 \end{BMAT} & & \\ & \begin{BMAT}{|c|c|}{|c|c|} A_2 & \\ & A_3 \end{BMAT} \end{array} \right)$

\end{document}


-