# Boxes within a Dotted Box

How do I create the dotted box? For the rest of the diagram I used a matrix, but I'm having trouble creating that box. Here's the code I used.

\begin{center}
$\begin{matrix}$ x(n)$\rightarrow \boxed{T} \rightarrow \boxed{[ \hspace{0.25 cm}]^2} \rightarrow &\bigoplus& \rightarrow T[x(n)]$ $\\ $$&\uparrow& \\$$& 7&$
$\end{matrix}$
\end{center}

Two approaches:

1. The first one uses your code (slightly modified) and the tikzmark library from TikZ to place some marks in the diagram; those marks are then used to draw the dashed box (the document needs to be processed twice to stabilize).

2. The whole diagram is drawn using TikZ; I used a chain, but other approaches are possible, of course. Then the fit library was used to draw the dashed box.

The code:

\documentclass{article}
\usepackage{amsmath}
\usepackage{amssymb}
\usepackage{tikz}
\usetikzlibrary{tikzmark,chains,fit,positioning}

\begin{document}

$\begin{matrix} x(n)\rightarrow\tikzmark{start}\boxed{T} \rightarrow \boxed{[ \hspace{0.25 cm}]^2} \rightarrow & \bigotimes\tikzmark{end} & \rightarrow T[x(n)] \\ &\uparrow& \\ & 7& \end{matrix}$

\begin{tikzpicture}[remember picture,overlay]
\draw[dashed]
([shift={(-8pt,-1cm)}]pic cs:start)
rectangle
([shift={(15pt,0.7cm)}]pic cs:end);
\end{tikzpicture}

$\begin{tikzpicture}[ start chain, every join/.style={->}, shorten >= 5pt, shorten <= 5pt, node distance=0.8cm and 0.8cm ] \node[on chain,join] {x(n)}; \node[draw,on chain,join] (T) {T}; \node[draw,on chain,join] {[\hspace{0.25 cm}]^2}; \node[draw,circle,on chain,join] (otimes) {\times}; \node[on chain,join] {T[x(n)]}; \node[below=of otimes] (seven) {7}; \draw[->] (seven) -- (otimes); \node[draw,inner xsep=12pt,dashed,fit={(T) (otimes) (seven)}] {}; \end{tikzpicture}$

\end{document}

TiKZ, of course, is a better solution:

Here I use a simple approach with positioning library to automatically place your figure elements. To create the dashed box, fit library again is the best choice.

\documentclass{article}
\usepackage{amsmath,tikz}
\usetikzlibrary{fit,positioning,arrows}
\begin{document}

\begin{tikzpicture}[>=latex',node distance=.7cm]
\node(xn) {$x(n)$};
\node(bt) [right=of xn,draw]{$T$};
\node(sq) [right=of bt,draw]{$[\hspace{0.25cm}]^2$};
\node(ot) [circle,draw,right=of sq,inner sep=0pt]{$\times$};
\node(tx) [right=of ot]{$T[x(n)]$};
\node(sv) [below=of ot,outer sep=0pt]{7};
\node[draw,inner sep=7pt,dashed,fit={(bt) (ot) (sv)}] {};
\path[->](xn)edge(bt)
(bt)edge(sq)
(sq)edge(ot)
(ot)edge(tx)
(sv)edge(ot);
\end{tikzpicture}

\end{document}