Source code
\documentclass[a4paper,twoside]{article}
\usepackage{upquote}
\usepackage{pgfkeys}
\usepackage{graphicx}
\usepackage{listings}
\usepackage{courier}
\usepackage{caption}
\DeclareCaptionFont{white}{\color{white}}
\DeclareCaptionFormat{listing}{\parbox{\textwidth}{\colorbox{gray}{\parbox{\textwidth}{#1#2#3}}\vskip-4pt}}
\captionsetup[lstlisting]{format=listing,labelfont=white,textfont=white}
\lstset{
basicstyle=\footnotesize\ttfamily,
numbers=left,
numberstyle=\tiny,
stepnumber=2,
numbersep=5pt,
tabsize=2,
extendedchars=true,
breaklines=true,
keywordstyle=\color{red},
stringstyle=\color{blue}\ttfamily,
showspaces=false,
showtabs=false,
xleftmargin=6pt,
framexleftmargin=6pt,
framexrightmargin=6pt,
framexbottommargin=4pt,
backgroundcolor=\color{yellow},
showstringspaces=false
}
\usepackage{aeguill}
\usepackage{prerex}
\usepackage{helvet}
\renewcommand{\rmdefault}{\sfdefault}
\usepackage[printonlyused,withpage]{acronym}%
\usetikzlibrary{chains,positioning}
\usepackage{verbatim}
\usepackage{xcolor}
\usepackage{pdfpages}
\DefineNamedColor{named}{BrickRed}{cmyk}{0,0.89,0.94,0.28}
\DefineNamedColor{named}{DarkRed}{cmyk}{0.4,0.89,0.94,0.28}
\renewcommand{\familydefault}{\sfdefault}
\usetikzlibrary{calc,shapes,positioning,arrows,positioning,shapes.geometric,fit,trees}
\usetikzlibrary{arrows,calc,fit}
\tikzset{box/.style={draw, rectangle, rounded corners, thick, node distance=7em, text width=6em, text centered, minimum height=3.5em}}
\tikzset{container/.style={draw, rectangle, dashed, inner sep=2em}}
\tikzset{line/.style={draw, thick, -latex'}}
\tikzstyle{every picture}=[sibling distance=3cm, shorten >=1pt, node distance=2cm]%>=stealth', bend angle=10, auto, initial text=]
\newcommand*{\stereotype}[1]{
\guillemotleft {#1}\guillemotright%
}
\usepackage{tikz}
%\usepackage{tikz-uml}
%\usepackage{pgf-umlsd}
\usepackage{lmodern,smartdiagram}
\smartdiagramset{set color list={
white!20!white,
white!20!white,
white!70!white,
white!40!white,
white!20!white,
} }
\tikzstyle{b} = [rectangle, draw, fill=blue!20, node distance=4.5cm, text width=8em, text centered, rounded corners, minimum height=4em, thick]
\tikzstyle{c} = [rectangle, draw, node distance=3cm, minimum height=1cm, minimum width=1cm, dashed]
\tikzstyle{l} = [draw, -latex,thick]
\usepackage{epsfig}
\usepackage[ruled,vlined]{algorithm2e}
\usepackage[T1]{fontenc}
\usepackage{amsmath}
\usepackage{amssymb}
\usepackage{amsmath, amsthm, amssymb, amsfonts}
\interdisplaylinepenalty=2500
\usepackage[cmintegrals]{newtxmath}
\hyphenation{op-tical net-works semi-conduc-tor}
\usepackage{epsfig}
\usepackage{subfigure}
\usepackage{calc}
\usepackage{amssymb}
\usepackage{amstext}
\usepackage{multicol}
\usepackage{pslatex}
\usepackage{apalike}
%\usepackage{SCITEPRESS} % Please add other packages that you may need BEFORE the SCITEPRESS.sty package.
\subfigtopskip=0pt
\subfigcapskip=0pt
\subfigbottomskip=0pt
\begin{document}
$\hat{\boldsymbol{U}}_{K}$ and its old position $\hat{\boldsymbol{X}}_{K}$ at k:
\begin{equation}
\hat{\boldsymbol{X}}_{k+1}=f(\hat{\boldsymbol{X}}_{k},\hat{\boldsymbol{U}}_{k})=\left[\begin{array}{c}x_{k+1}\\y_{k+1}\\ \theta_{k+1} \end{array}\right]=\left[\begin{array}{c} x_{k}+\Delta D_{k}\cos\theta_{k}\\y_{k}+\Delta D_{k}\sin\theta_{k}\\ \theta_{k}+\Delta \theta_{k} \end{array}\right]
\end{equation}
Where $\Delta D_{k}$, $\Delta \theta_{k}$, $X_{k}$ and $U_{k}$ are:
\end{document}
Best Answer
Your preamble is quite a mess. It's difficult to understand what is the font you want to use. In any case, there are several packages you must not load.
aeguill
is obsolete and deprecatedpgfkeys
is loaded bytikz
epsfig
is deprecatedlmodern
is quite useless if you loadhelvet
and set sans serif as defaultsubfigure
is obsolete and should not be loaded along withcaption
anywaypslatex
is obsoleteI left them, but
\tikzstyle
is deprecated.