Capsula del Frontend de PGF En LaTeX

\documentclass{article}
\usepackage[utf8]{inputenc}
\usepackage{geometry} [a4paper,lmargin=1.5cm,rmargin=1.5cm,Botton=1.5cm,top=1.75cm]
\usepackage{graphicx}
\usepackage{wrapfig}
\usepackage{color}
\usepackage{amsmath}
\usepackage[T1]{fontenc}
\usepackage{amsfonts}
\usepackage{amssymb}
\usepackage{cancel}
\usepackage[all]{xy}
\usepackage{pst-all}
\usepackage{fancybox}
\usepackage{tikz}
\usepackage{gnuplottex}
\tikzset{flippedeventlabel/.append style={align=center}}
\usetikzlibrary{matrix.skeleton}
\usetikzlibrary[shapes,arrows,positioning,fit,backgrounds,intersections,shadows,calc]
\usetikzlibrary{positioning} \usetikzlibrary{decorations.text} \usetikzlibrary{decorations.pathmorphing}

\usepackage{pgfplots}
\pgfplotsset{compat=newest}
\usetikzlibrary{datavisualization} \usetikzlibrary[shapes,arrows,positioning,fit,backgrounds,intersections,shadows,calc,datavisualization.formats.functions]
\usetikzlibrary{patterns}
\usepackage[colorlinks=true,linkcolor=black,citecolor=black,filecolor=magenta,urlcolor=blue]{hyperref}
%Paquete de estilo de referencias
\urlstyle{same}
\title{Una Pequeña Cápsula Del \texttt{Frontend Layer} de \texttt{PGF} En \LaTeX}
\author{Nimrod Rodríguez}
% Start the document
\begin{document}
\maketitle
\section*{La Suma De Riemann-Stieltjes} El excelente recurso del \texttt{frontend layer} de \texttt{PGF} para programar texto con gráficos.\\

\begin{tikzpicture}[scale =1,domain=-2.5:4, axes/.style= impotant line/.style={very thick},information text/.style={rounded corners, fill=blue,inner sep=2ex}]

\draw (1.5,8.5) [xshift=1.85cm,black!90]  node  [text width=6cm, information text]
{\begin{minipage}{2.5in}
 \bf\color{white}
\begin{center}
\shadowbox{Riemann-Stieltjes}\\
\end{center}
La figura muestra una ilustración de la suma de Riemann-Stieltjes, para el "área bajo la curva" de la función impar cúbica, utilizando el entorno resumido de \texttt{\textbackslash begin \{axis\}} y \texttt{\textbackslash end \{axis\}}, el cual facilita el manejo coordenado al utilizar \texttt {\textbackslash draw} (para agregar etiquetas), y \texttt {\textbackslash fill} (para estilizar el gráfico).
\end{minipage}};
\begin{axis}[color=blue]
\draw[->, black,dashed] (-2.5,0)--(4.2,0) node[right]{$x$};
\draw[->,black,dashed] (0,-5)--(0,18) node[right]{$y$};
\draw[-] (-2,0)--(-2,-8);
\draw[-] (3,0)--(3,27);
\addplot[color=magenta,very thick] {x*x*x};
\draw node at (1,65) {$\textcolor{magenta}{f(x)= x^3}$};
\fill[blue] plot[domain=-2:0] (\x,\x * \x * \x )--(-2,0)--(-2,-8)--cycle;
\fill[blue] plot[domain=0:2] (\x,\x * \x * \x )--(2,0)--(0,0)--cycle;
\fill[green!65!blue!60!black] plot[domain=2:3.5] (\x,\x * \x * \x )--(3.5,0)--(2,0)--(2,8)--cycle;
\draw (-0.5,45) node {$\displaystyle\int_{-2}^{\frac{7}{2}} \!\!x^3\mathrm{d}x=\textcolor{green!65!blue!60!black}{\displaystyle\int_{2}^{\frac{7}{2}} \!\!x^3\mathrm{d}x}$};
\draw (-0.5,30) node {$\frac{1}{4}x^4\textcolor{black}{\displaystyle\mid}_{-2}^{\frac{7}{2}}=\textcolor{green!65!blue!60!black}{\frac{1}{4}x^4\textcolor{black}{\displaystyle\mid}_{2}^{\frac{7}{2}}}=\textcolor{green!65!blue!60!black}{33\frac{33}{64}\ unds^2}$};
\draw (-2,0)node[above=0.3cm]{-2};
\draw[-] (-2,1)--(-2,4);
\draw (0,0)node[below=0.3cm]{0};
\draw[-] (0,-1)--(0,-4);
\draw (2,0)node[below=0.3cm]{2};
\draw[-] (2,-1)--(2,-4);
\draw (3.5,0)node[below=0.3cm]{$3\frac{1}{2}$};
\draw[-] (3.5,-1)--(3.5,-4);
\draw node at (1.75,3) {\bf\textcolor{white}{\tiny{+}}};
\draw node at (-1.75,-3) {\bf\textcolor{white}{\tiny{-}}};
\end{axis}
\end{tikzpicture}
\end{document}