\documentclass[DIV=9, pagesize=auto]{scrartcl} \usepackage{fixltx2e} \usepackage{lmodern} \usepackage[T1]{fontenc} \usepackage{textcomp} \usepackage{amsmath} \usepackage{cases} \usepackage{microtype} \usepackage{hyperref} \newcommand*{\fancybreak}{% \par \nopagebreak\medskip\nopagebreak \noindent\null\hfill$*\quad*\quad*\quad$\hfill\null\par \nopagebreak\medskip\pagebreak[0]% } \newcommand*{\mail}[1]{\href{mailto:#1}{\texttt{#1}}} \newcommand*{\pkg}[1]{\textsf{#1}} \newcommand*{\cmd}[1]{\texttt{\string#1}} \newcommand*{\env}[1]{\texttt{#1}} \newcommand*{\meta}[1]{\textlangle\textsl{#1}\textrangle} \addtokomafont{title}{\rmfamily} \title{The \pkg{cases} package\thanks{This manual corresponds to \pkg{cases}~v2.5, dated~May 2002.}} \author{Donald Arseneau\\\mail{asnd@triumf.ca}} \date{May 2002} \begin{document} \maketitle \begingroup \small \noindent Copyright \textcopyright~1993, 1994, 1995, 2000, 2002 by Donald Arseneau, \mail{asnd@triumf.ca}. These macros may be freely transmitted, reproduced, or modified provided that this notice is left intact. Sub-equation numbering is based on \pkg{subeqn.sty} by Stephen Gildea; most of the rest is based on \LaTeX's \cmd{\eqnarray} by Leslie Lamport and the \LaTeX3 team. \par \endgroup \fancybreak This provides a \LaTeX\ environment \verb+{numcases}+ to produce multi-case equations with a separate equation number for each case. There is also \verb+{subnumcases}+ which numbers each case with the overall equation number plus a letter [8a, 8b, etc.]. The syntax is % \begin{verbatim} \begin{numcases}{left_side} case_1 & explanation_1 \\ case_2 & explanation_2 \\ ... case_n & explanation_n \end{numcases} \end{verbatim} % Each \meta{case} is a math formula, and each \meta{explanation} is a piece of lr mode text (which may contain math mode in \verb+\(...\)+ or \verb+$...$+). The explanations are optional. Equation numbers are inserted automatically, just as for the \env{eqnarray} environment. In particular, the \cmd{\nonumber} command suppresses an equation number and the \cmd{\label} command allows reference to a particular case. In a \env{subnumcases} environment, a \cmd{\label} in the \meta{left\_side} of the equation gives the overall equation number, without any letter. To use this package, include ``\verb+\usepackage{cases}+'' after ``\cmd{\documentclass}''. You may also specify ``\verb+\usepackage[subnum]{cases}+'' to force \emph{all} \env{numcases} environments to be treated as \env{subnumcases}. \emph{Question:} Is there a \verb+{numcases*}+ environment for unnumbered cases?\\ \emph{Answer:} There is a \verb+{cases}+ environment in \AmS-\LaTeX, but it is just as convenient to stick with the canonical \LaTeX\ array: % \begin{verbatim} \[ left side = \left\{ \begin{array}...\end{array} \right. \] \end{verbatim} % Speaking of \pkg{\AmS-math}, they use an entirely different system of equation numbering, and this package uses ordinary \LaTeX\ % numbering. \fancybreak \noindent A simple example is: % \begin{verbatim} \begin{numcases}{|x|=} x, & for $x \geq 0$\\ -x, & for $x < 0$ \end{numcases} \end{verbatim} % Giving: % \begin{numcases}{|x|=} x, & for $x \geq 0$\\ -x, & for $x < 0$ \end{numcases} \fancybreak \noindent Another example is calculating the square root of $c+id$. First compute \phantomsection \begin{subnumcases}{\label{w} w\equiv} 0 & $c = d = 0$\label{wzero}\\ \sqrt{|c|}\,\sqrt{\frac{1 + \sqrt{1+(d/c)^2}}{2}} & $|c| \geq |d|$ \\ \sqrt{|d|}\,\sqrt{\frac{|c/d| + \sqrt{1+(c/d)^2}}{2}} & $|c| < |d|$ \end{subnumcases} Then, using $w$ from eq.~(\ref{w}), the square root is \begin{subnumcases}{\sqrt{c+id}=} 0 & $w=0$ (case \ref{wzero})\\ w+i\frac{d}{2w} & $w \neq 0$, $c \geq 0$ \\ \frac{|d|}{2w} + iw & $w \neq 0$, $c < 0$, $d \geq 0$ \\ \frac{|d|}{2w} - iw & $w \neq 0$, $c < 0$, $d < 0$ \end{subnumcases} \pagebreak[2] \noindent This was produced by: % \small \begin{verbatim} Another example is calculating the square root of $c+id$. First compute \begin{subnumcases}{\label{w} w\equiv} 0 & $c = d = 0$\label{wzero}\\ \sqrt{|c|}\,\sqrt{\frac{1 + \sqrt{1+(d/c)^2}}{2}} & $|c| \geq |d|$ \\ \sqrt{|d|}\,\sqrt{\frac{|c/d| + \sqrt{1+(c/d)^2}}{2}} & $|c| < |d|$ \end{subnumcases} Then, using $w$ from eq.~(\ref{w}), the square root is \begin{subnumcases}{\sqrt{c+id}=} 0 & $w=0$ (case \ref{wzero})\\ w+i\frac{d}{2w} & $w \neq 0$, $c \geq 0$ \\ \frac{|d|}{2w} + iw & $w \neq 0$, $c < 0$, $d \geq 0$ \\ \frac{|d|}{2w} - iw & $w \neq 0$, $c < 0$, $d < 0$ \end{subnumcases} \end{verbatim} \end{document}