A diagram with matrices

Question

I want to draw the following diagram which contains two matrices (2x2 on left and 4x4 on right) and a box. Could someone help?

Answer 1

With some motivations from @Alain Matthes answer: Tikz: Arrowheads in the center

This could be a starting point for your quest:

\documentclass{article}
\usepackage{amsmath}
\usepackage{tikz}
\usetikzlibrary{arrows}
\usetikzlibrary{decorations.markings}

\begin{document}
\pagestyle{empty}
%
\tikzstyle{int}=[draw, minimum size=2em]
\tikzset{->-/.style={decoration={
            markings,
            mark=at position #1 with {\arrow{>}}},postaction={decorate}}}
\begin{tikzpicture}[node distance=2.5cm, auto]
    \node [int] (a) {DST};
    \node (b) [left of=a, coordinate] {a};
    \node (c) [right of=a, coordinate] {a};
    \draw[dashed, ->-=0.5] (b) --(a);   
    \draw[dashed, ->-=0.5] (a) --(c);   
    \node        (d) [right of=c,shift={(-1.1cm,0mm)}]{$\begin{pmatrix}
        c&c&v&b\\
        a&b&c&d\\
                a&b&c&d\\
                        a&b&c&d
        \end{pmatrix}$};
    \node        (e) [right of=b, shift={(-3.1cm,0mm)}]{$\begin{pmatrix}
        c&c\\
        a&b
        \end{pmatrix}$};    
\end{tikzpicture}

\end{document}

which would give:

Note: Since your arrows are not aligned in the center, I used the macro option from the answer to play with the placement of the arrows as you define. For more information on how-to, please refer the link given above.

Answer 2

Rather similar to Raaja's nice answer except that I am using tikzmark to annotate an ordinary equation, such that identations are unchanged. And the TikZ path can be done in one stroke.

\documentclass[fleqn]{article}
\usepackage{amsmath}
\usepackage{tikz}
\usetikzlibrary{tikzmark}
\usetikzlibrary{decorations.markings}
% from https://tex.stackexchange.com/a/39282/121799
\tikzset{->-/.style={decoration={
            markings,
            mark=at position #1 with {\arrow{>}}},postaction={decorate}}}
\begin{document}
\[
\tikzmarknode{L}{\begin{pmatrix}
 1 & 2 \\ 3 & 4
\end{pmatrix}}
\qquad\qquad\qquad\qquad\qquad\qquad
\tikzmarknode{R}{\begin{pmatrix}
 1 & 2 & 3 & 4 \\
 5 & 6 & 7 & 8 \\
 9 & 10 & 11 & 12 \\
 13 & 14 & 15 & 16 \\
\end{pmatrix}}
\]
\begin{tikzpicture}[overlay,remember picture]
 \draw[>=latex,dashed,->-=0.2,->-=0.8] (L) -- (R)
 node[midway,fill=white,draw,solid]{DST};
\end{tikzpicture}
\end{document}