# Issue with subequation environment

I use the following code

\begin{subequations}
$$\mid H(j\omega) \mid = \frac{\omega CR}{\sqrt{1+(\omega CR)^2}} \label{subeqn:amplitude}$$
$$\angle H = 90^o - arctan(\omega CR) \label{subeqn:phase}$$
\end{subequations}


However I get 5 errors

1. Extra \else
2. Missing \endcsname inserted
3. Incomplete \iffalse; all text was ignored after line 329 (This is line "")
4. Emergency stop
5. Fatal Error occurred; no output pdf file produced.

I already use amsmath in my preamble.

My minimal Example is

\documentclass[12pt,a4paper]{article}
\usepackage{amsmath}
\begin{document}
\begin{subequations}
\begin{gather}
\lvert H(j\omega) \rvert = \frac{\omega CR}{\sqrt{1+(\omega CR)^2}}
\label{subeqn:amplitude}
\\
\angle H = 90^\circ - \arctan(\omega CR)
\label{subeqn:phase}
\end{gather}
\end{subequations}

\end{document}


Typing the aforementioned code produces no error. So I believe that there must be sth wrong in the preamble, which is

\documentclass[12pt,a4paper]{article}
\usepackage[english,greek]{babel}
\usepackage[iso-8859-7]{inputenc}
\usepackage{kerkis}
\usepackage{amsmath}
\usepackage{amssymb}
\usepackage{amsfonts}
\usepackage{amsthm}
\usepackage{units}
\usepackage{array}
\usepackage{framed} % ãéá ãêñé background ðßóù áðü êÜðïéá paragraphs
\usepackage{extarrows}
\usepackage{cancel}
\usepackage[pdftex]{graphicx}
%\usepackage[twoside,pdftex,total={16.4cm,24cm}, left=2.9cm, top=3.2cm, headsep=1.4cm]            {geometry}
%\usepackage[top=3.2cm, bottom=3.4cm, left=2.9cm, right=2.9cm,headsep=0.8cm]{geometry}
\usepackage[margin=2.8cm]{geometry}
\usepackage[Bjornstrup]{fncychap}
\usepackage{fancybox}
\usepackage{fancyhdr}
\usepackage{colortbl}
\usepackage{xcolor}
\usepackage{footmisc}
\usepackage{subfiles}
\usepackage{float}
\usepackage{slashbox}
%\usepackage{float}
%\restylefloat{figure}
%_________________________________________________________________________________________

\usepackage{hyperref}
\usepackage{subfigure}
\renewcommand{\labelitemi}{$\circ$}
\usepackage{wrapfig}
\usepackage{color}
%\usepackage[usenames,dvipsnames]{color}
\definecolor{Darkgreen}{rgb}{0,0.4,0}
\definecolor{Darkblue}{rgb}{0,0,0.4}
\newcommand{\HRule}{\rule{\linewidth}{0.8mm}}
\usepackage{rotating}
%\usepackage[landscape]{geometry}
\usepackage{lscape}
\usepackage{cancel}
\usepackage{fancyvrb}
%\usepackage{yannisgr}
\usepackage{listings}
%\lstset{ %
%language=matlab,                % choose the language of the code
%basicstyle=\footnotesize,       % the size of the fonts that are used for the code
%numbers=left,                   % where to put the line-numbers
%numberstyle=\footnotesize,      % the size of the fonts that are used for the line-     numbers
%stepnumber=1,                   % the step between two line-numbers. If it is 1 each    line will be numbered
%numbersep=5pt,                  % how far the line-numbers are from the code
%backgroundcolor=\color{white},  % choose the background color. You must add     \usepackage{color}
%showspaces=false,               % show spaces adding particular underscores
%showstringspaces=false,         % underline spaces within strings
%showtabs=false,                 % show tabs within strings adding particular    underscores
%frame=single,           % adds a frame around the code
%tabsize=2,          % sets default tabsize to 2 spaces
%captionpos=b,           % sets the caption-position to bottom
%breaklines=true,        % sets automatic line breaking
%breakatwhitespace=false,    % sets if automatic breaks should only happen at   whitespace
%escapeinside={\%*}{*)}          % if you want to add a comment within your code
%}
\usepackage{textcomp}
\definecolor{listinggray}{gray}{0.9}
\definecolor{lbcolor}{rgb}{0.9,0.9,0.9}
\lstset{
backgroundcolor=\color{lbcolor},
tabsize=4,
rulecolor=,
language=matlab,
basicstyle=\scriptsize,
upquote=true,
aboveskip={1.5\baselineskip},
columns=fixed,
showstringspaces=false,
extendedchars=true,
breaklines=true,
prebreak = \raisebox{0ex}[0ex][0ex]{\ensuremath{\hookleftarrow}},
frame=single,
showtabs=false,
showspaces=false,
showstringspaces=false,
identifierstyle=\ttfamily,
keywordstyle=\color[rgb]{0,0,1},
commentstyle=\color[rgb]{0.133,0.545,0.133},
stringstyle=\color[rgb]{0.627,0.126,0.941},
}
%\usepackage{subeqn}

%_________________________________________________________________________________________

\definecolor{mygray}{gray}{.75}%{.9, .9, .9}
\definecolor{lightgray}{gray}{.8}%{.9, .9, .9}
\definecolor{shadecolor}{gray}{.90} %gia framed package
%\definecolor{mygray}{rgb}{.9, .9, .9} %enallaktika !! anti gia panw
\newcommand*\mygraybox[1]{\colorbox{mygray}{\hspace{1em}#1\hspace{1em}}}

%\renewcommand{\topfraction}{0.85}%gia na min uparxoun 2 figures se mia selida kai   tipota allo
\renewcommand{\textfraction}{0.1}
\renewcommand{\floatpagefraction}{0.75}

\newcommand{\kai}{\quad \text{êáé} \quad}
\newcommand{\kkai}{\qquad \text{êáé} \qquad}

\linespread{1.1}
\newcommand{\sw}{\selectlanguage{english}}
\newcommand{\sq}{\selectlanguage{greek}}
\newcommand{\eng}[1]{\latintext#1\greektext}
\newcommand{\gre}[1]{\greektext\latintext#1}
\newcolumntype{C}[1]{>{\centering\let\newline\\\arraybackslash\hspace{0pt}}m{#1}}

\begin{comment}
\let\origdoublepage\cleardoublepage
\newcommand{\clearemptydoublepage}{%
\clearpage
{\pagestyle{empty}\origdoublepage}%
}
\let\cleardoublepage\clearemptydoublepage

\pagestyle{fancy}
\renewcommand{\chaptermark}[1]{\markboth{#1}{}}
\renewcommand{\sectionmark}[1]{\markright{\thesection\ #1}}
\fancyhf{} % delete current setting for header and footer
\fancyhead[LE,RO]{\bfseries\thepage}
\fancyhead[LO]{\rightmark}
\fancyhead[RE]{\leftmark}
\renewcommand{\headrulewidth}{0.5pt}
\renewcommand{\footrulewidth}{0pt}
\addtolength{\headheight}{0.5pt} % make space for the rule      %Ôï ÷ù ïñßóåé 0.8 áð ôï  package
\fancypagestyle{plain}{%
\fancyhead{} % get rid of headers on plain pages
\renewcommand{\headrulewidth}{0pt} % and the line}

\newtheorem{thm}{Èåþñçìá}[chapter]
\newtheorem{cor}[thm]{Ðüñéóìá}
\newtheorem{lem}[thm]{ËÞììá}
\newtheorem{parad}{ÐáñÜäåéãìá}[chapter]
\newtheorem{defgr}{Ïñéóìüò}[chapter]
\end{comment}

\parskip 3mm
\footskip = 15mm

• Welcome to TeX.sx! Copy-pasting your code snippet into a compilable example yields no error for me, so you must be doing something different. Therefore, please add a minimal working example (MWE) that illustrates your problem. – lockstep Dec 17 '11 at 10:57
• This works for me too, simply with amsmath and the article class, nothing more. Btw. I recommend writing \arctan as operator, and using \circ instead of o. – Stefan Kottwitz Dec 17 '11 at 10:58
• The preamble does not seem to have problems (but it's not that pretty). The problem seems to be on the text that precedes the subequations environment. – egreg Dec 17 '11 at 12:18
• Since I erased \usepackage{hyperref} it works! However I need this package... – Thanos Dec 17 '11 at 12:25
• @Thanos: Does moving \usepackage{hyperref} towards the end of your preamble work? Since hyperref redefines a large number of standard LaTeX macros, it should usually be loaded last to maintain its usage. – Werner Dec 17 '11 at 22:01

## 1 Answer

I don't get any errors from that snippet, so the problem is somewhere else before that. The code can be improved:

\begin{subequations}
\begin{gather}
\lvert H(j\omega) \rvert = \frac{\omega CR}{\sqrt{1+(\omega CR)^2}}
\label{subeqn:amplitude}
\\
\angle H = 90^\circ - \arctan(\omega CR)
\label{subeqn:phase}
\end{gather}
\end{subequations}


Notice that \mid is not to be used for absolute value; the "degree" symbol is better typeset with ^\circ and math operators such as "arctan" have their command.

Don't use two consecutive math environments: amsmath provides many environments for this purpose, in this case gather is appropriate.

• @Thanos Please, add to your question rather than in comments that are of limited size. – egreg Dec 17 '11 at 11:29