# How to write equations with arrow and illustration

Sorry for boring you. I am wondering if someone knows how to write following equation in latex:

The main body of the equation is written in latex. However, the added blue arrows and explication smaller equations are added with powerpoint. Thank you very much for taking a look.

UPDATE: An arguably nicer alternative.

\documentclass{article}
\usepackage{amsmath}
\usepackage{tikz}
\newcommand{\tikznode}[3][inner sep=0pt]{\tikz[remember
picture,baseline=(#2.base)]{\node(#2)[#1]{$#3$};}}
\begin{document}
\begin{align*}
%
{\large \delta\boldsymbol{\omega}_n=
\tikznode{A}{\boldsymbol{A}}}&{\large\begin{bmatrix}
\tikznode{T}{\boldsymbol{T}}_{\boldsymbol{r}_{1,n}}\\
\tikznode{B}{\overline{\boldsymbol{B}}}\begin{bmatrix}
\boldsymbol{T}_{\boldsymbol{r}_{1,n}}\\
\tikznode{C}{\boldsymbol{C}}
\end{bmatrix}
\end{bmatrix}\delta\boldsymbol{Q}=\boldsymbol{B}_n\boldsymbol{q}}\\[0.5cm]
%
\tikznode[inner sep=1pt]{below1}{\scriptsize\delta\boldsymbol{\omega}\to\begin{matrix}\delta\boldsymbol{r}_1\\
\delta\boldsymbol{r}_2\\ \delta\boldsymbol{r}_3
\tikznode[inner sep=1pt]{below2}{\scriptsize\begin{matrix}\delta\boldsymbol{r}_1\\
\delta\boldsymbol{r}_2
\end{matrix}\to
\begin{matrix}
\delta\boldsymbol{r}_1\\ \delta\overline{\boldsymbol{r}}_1\\
\delta\boldsymbol{r}_2\\ \delta\boldsymbol{r}_3
\end{matrix}}
\tikznode[inner sep=1pt]{below3}{\scriptsize\begin{matrix}\delta\boldsymbol{r}_1\\
\delta\boldsymbol{r}_2\\ \delta\boldsymbol{r}_3
\end{matrix}\to \delta\boldsymbol{\omega}}
\end{align*}
\begin{tikzpicture}[overlay,remember picture,blue!30,thick]
\draw (above.south west) -- (above.south east);
\draw[-latex] (above.south) --(T);
%
\draw (below1.north west) -- (below1.north east);
\draw[-latex] (below1.north) --(A);
%
\draw (below2.north west) -- (below2.north east);
\draw[-latex] (below2.north) --(B);
%
\draw (below3.north west) -- (below3.north east);
\draw[-latex] (below3.north) --(C);
\end{tikzpicture}
\end{document}


ORIGINAL ANSWER: Here I show how to do the annotations. You'll have to adjust the sizes of the various symbols.

\documentclass{article}
\usepackage{amsmath}
\usepackage{tikz}
\newcommand{\tikznode}[2]{\tikz[remember
picture,baseline=(#1.base)]{\node(#1)[inner sep=0pt]{$#2$};}}
\begin{document}
\begin{align*}
%
{\large \delta\boldsymbol{\omega}_n=
\tikznode{A}{\boldsymbol{A}}}&{\large\begin{bmatrix}
\tikznode{T}{\boldsymbol{T}}_{\boldsymbol{r}_{1,n}}\\
\tikznode{B}{\overline{\boldsymbol{B}}}\begin{bmatrix}
\boldsymbol{T}_{\boldsymbol{r}_{1,n}}\\
\tikznode{C}{\boldsymbol{C}}
\end{bmatrix}
\end{bmatrix}\delta\boldsymbol{Q}=\boldsymbol{B}_n\boldsymbol{q}}\\[0.5cm]
%
\tikznode{below1}{\scriptstyle\delta\boldsymbol{\omega}\to\begin{matrix}\delta\boldsymbol{r}_1\\
\delta\boldsymbol{r}_2\\ \delta\boldsymbol{r}_3
\end{matrix}}&
\tikznode{below2}{\scriptstyle\begin{matrix}\delta\boldsymbol{r}_1\\
\delta\boldsymbol{r}_2
\end{matrix}\to
\begin{matrix}
\delta\boldsymbol{r}_1\\ \delta\overline{\boldsymbol{r}}_1\\
\delta\boldsymbol{r}_2\\ \delta\boldsymbol{r}_3
\end{matrix}}
~
\tikznode{below3}{\scriptstyle\begin{matrix}\delta\boldsymbol{r}_1\\
\delta\boldsymbol{r}_2\\ \delta\boldsymbol{r}_3
\end{matrix}\to \delta\boldsymbol{\omega}}
\end{align*}
\begin{tikzpicture}[overlay,remember picture,blue!30]
\draw (above.south west) -- ++(0,0.1);
\draw (above.south east) -- ++(0,0.1);
\draw (above.south west) -- (above.south east);
\draw[-latex] (T|- above.south) --(T);
%
\draw (below1.north west) -- ++(0,-0.1);
\draw (below1.north east) -- ++(0,-0.1);
\draw (below1.north west) -- (below1.north east);
\draw[-latex] (A|- below1.north) --(A);
%
\draw (below2.north west) -- ++(0,-0.1);
\draw (below2.north east) -- ++(0,-0.1);
\draw (below2.north west) -- (below2.north east);
\draw[-latex] (B|- below2.north) --(B);
%
\draw (below3.north west) -- ++(0,-0.1);
\draw (below3.north east) -- ++(0,-0.1);
\draw (below3.north west) -- (below3.north east);
\draw[-latex] (C|- below3.north) --(C);
\end{tikzpicture}
\end{document}