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% C A S E S . S T Y ver 3.1 Mar 2020
%
% Copyright (C) 1993,1994,1995,2000,2002,2020 by Donald Arseneau
% 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 subeqn.sty by Stephen Gildea; most of the rest is based
% on LaTeX's \eqnarray by Leslie Lamport and the LaTeX3 team,
% and parts of amsmath.sty by the American Mathematical Society.
%
% This provides a LaTeX environment {numcases} to produce multi-case
% equations with a separate equation number for each case. There is
% also {subnumcases} which numbers each case with the overall equation
% number plus a letter [8a, 8b, etc.]. The syntax is
%
% \begin{numcases}{left_side}
% case_1 & explanation_1 \\
% case_2 & explanation_2 \\
% ...
% case_n & explanation_n
% \end{numcases}
%
% Each case is a math formula, and each explanation is a piece of lr mode
% text (which may contain math mode in \(...\) or $...$). The explanations
% are optional. Equation numbers are inserted automatically, just as for
% the eqnarray environment. In particular, the \nonumber command suppresses
% an equation number and the \label command allows reference to a particular
% case. In a subnumcases environment, a \label in the left_side of the
% equation gives the overall equation number, without any letter.
%
% For detailed description and package options, see cases.pdf (cases.tex).
\ProvidesPackage{cases}[2020/03/10 ver 3.1]
\newdimen\numc@numwid
% copy \@@eqncr but change error message and handle \tag for amsmath:
\def\@@numc@cr{\let\reserved@a\relax
\ifcase\@eqcnt \def\reserved@a{& & &}\or \def\reserved@a{& &}%
\or \def\reserved@a{&}\else
\let\reserved@a\@empty
\@latex@error{Too many columns in numcases environment}\@ehc\fi
\reserved@a \if@eqnsw\@eqnnum\stepcounter{equation}\else \iftag@ \df@tag\fi\fi
\global\@eqnswtrue\global\@eqcnt\z@\cr}
\let\iftag@=\iffalse
\newenvironment{numcases}[1]%
{$$\numc@opts
\refstepcounter{equation}% Needed for LHS \label
\setbox\z@\hbox {% typeset LHS
\def\@currentlabel{\p@equation\theequation}% local def
$\displaystyle {#1{}}\m@th$}%
\numc@setsub % maybe \subequations (handling \refstepcounter)
\def\@currentlabel{\p@equation\theequation}%
\global\@eqnswtrue\m@th
\let\tag\numc@tag
\settowidth{\numc@numwid}{\ \advance\c@equation\tw@\numc@eqnnum}%
\@tempskipb\@centering
\ifx\numc@left\mathindent % fleqn:
\@tempskipa=\@ne\mathindent\@minus\@ne\mathindent
\ifx\numc@forcenumwid\z@ % leqno
\ifdim \numc@numwid>\mathindent % enlarge left space for equation number
\@tempskipa=\numc@numwid\@minus\numc@numwid
\fi\fi
\else % not fleqn:
\@tempskipa=\@centering
\advance\@tempskipa \numc@numwid\@minus\numc@numwid
\advance\@tempskipa \numc@numwid\@minus\numc@forcenumwid
\advance\@tempskipb \tw@\numc@numwid\@minus\tw@\numc@numwid
\advance\@tempskipb -\numc@forcenumwid\@minus-\numc@forcenumwid
\fi
\setbox\tw@\vbox\bgroup
\everycr{}\let\\\@eqncr \let\@@eqncr\@@numc@cr
\tabskip\@tempskipa
\halign to\dimen@ii \bgroup % white space for LHS followed by RHS
\kern\wd\z@ \kern10\p@ % assume (and force) width of brace
\global\let\iftag@=\iffalse % for amsmath (make sure this is not in \if block)
\global\@eqcnt\@ne $\numc@dispstyle ##\relax$\hfil
\tabskip\z@skip &% explanation
\global\@eqcnt\tw@
\numc@expstyle\quad ##\unskip\numc@expstyle\hfil % \unskip removes quad if no explanation
\tabskip\@tempskipb &% equation number
\global\@eqcnt\thr@@\hbox to\numc@forcenumwid\bgroup\hss##\egroup
\tabskip\z@skip\cr
}{%
\@@numc@cr \egroup % end \halign, which does not contain first column or brace
\global\advance\c@equation\m@ne
% Measure the natural width of the alignment
\unskip\unpenalty\unskip\unpenalty \setbox\z@\lastbox % grab last line
\nointerlineskip \copy\z@ % then put it back
\global\dimen@i\wd\z@
\setbox\z@\hbox{\unhbox\z@}% Measure its natural width in \dimen@i
\global\dimen@i\wd\z@
\egroup% end \vbox (\tw@) box\z@ is restored to LHS; \dimen@i is retained
\advance\dimen@i-\@tempskipa \advance\dimen@i-\wd\z@ \advance\dimen@i-10\p@
\advance\dimen@i-\@tempskipb
% now \@dimen@i is natural width of RHS + explanation + eqno columns
\hbox to\wd\tw@{\m@th % assemble the whole equation stretched to display width
\hskip\@tempskipa
\box\z@ % LHS - parameter #1
\hbox to10\p@{\hss$\displaystyle
\dimen@\ht\tw@ \advance\dimen@\dp\tw@ % get size of brace
\ifdim\dimen@<1.5em\dimen@=1.5em\fi % don't allow really small brace
\left\lbrace\vcenter to\dimen@{\vfil}\,\right.\n@space % make brace
$\hss}% end 10pt brace box
\kern\dimen@i
\hskip\@tempskipb
}% finished first part (filled whole line) end the \hbox to\wd\tw@
\kern-\wd\tw@ % backspace the full width
\vcenter{\box\tw@}% overlay the alignment
\numc@resetsub
$$\global\@ignoretrue}
% a wrapper around \subequations so it works in cases with hyperref and amsmath
\def\numc@subequations{% skip the \refstepcounter inside \subequations
\let\numc@opts\refstepcounter
\def\refstepcounter##1{\let\refstepcounter\numc@opts}%
\subequations
\refstepcounter{equation}}
\let\numc@setsub\relax
\let\numc@resetsub\relax
\def\subnumcases{%
\let\numc@setsub\numc@subequations
\let\numc@resetsub\endsubequations
\numcases}
\let\endsubnumcases\endnumcases
% declare subequations -- either defining them following the style of
% Gildea's subeqn.sty, or using the version from AMS-LaTeX if that is loaded.
\@ifundefined{c@parentequation}{% No AMS
\def\numc@eqnnum{\@eqnnum}
% for \tag (but not \tag*) without amsmath, using \@@numc@cr above.
\def\numc@tag#1{\def\@currentlabel{#1}%
\gdef\df@tag{\def\theequation{#1}\@eqnnum}%
\global\let\iftag@=\iftrue
\nonumber}
%
% These versions of subequations follow the style of Gildea's subeqn.sty,
% but are thoroughly rewritten.
%
% You can change the labelling by redefining \thesubequation, but the names
% of the counters may be confusing: The sub-number is given by counter
% {equation}, while the overall equation number is given by {mainequation}.
% There are two ways to reference the overall equation number:
% through the value of \c@mainequation, as in \Roman{mainequation}, or
% through \themainequation, which gives the text of the normal \theequation.
% Refer to the local sub-number with \c@equation, as in \alph{equation}.
% The default numbering is like 13c, given by:
%
\def\thesubequation{\themainequation\alph{equation}}
%
% Some alternatives:
% \def\thesubequation{\themainequation.\Alph{equation}} % 13.C
% \def\thesubequation{\themainequation-\roman{equation}} % 13-iii
% \def\thesubequation{(\arabic{mainequation}\alph{equation})} % (13c)
% The third alternative should be used if a document style has
% declared \renewcommand{\@eqnnum}{\theequation} and
% \renewcommand{\theequation}{(\arabic{equation})}, which makes
% \ref put parentheses around regular equation numbers automatically.
%
\def\subequations{\refstepcounter{equation}%
\mathchardef\c@mainequation\c@equation
\let\@tempa\protect % * added protection
\def\protect{\noexpand\protect\noexpand}% *
\edef\themainequation{\theequation}\let\theequation\thesubequation
\let\protect\@tempa % *
\global\c@equation\z@}
%
\def\endsubequations{%
\global\c@equation\c@mainequation
\global\@ignoretrue}
%
% \begin{subeqnarray} works like \begin{subequations}\begin{eqnarray},
% with the added feature that a \label command given given at the very
% beginning of the first entry defines a label for the overall equation
% number.
%
\def\subeqnarray{\subequations\eqnarray\@ifnextchar\label{\@lab@subeqnarray}{}}
\def\endsubeqnarray{\endeqnarray\endsubequations}
\def\@lab@subeqnarray#1#2{\begingroup
\let\@currentlabel\themainequation #1{#2}\endgroup}
%
}{% AMS
% \subequations already defined;
% use tag format
\def\numc@eqnnum{\tagform@{\theequation}}
\def\numc@tag{\tag@in@align}
% add little space after brace to amsmath's cases
\def\@tempa{%
\let\@ifnextchar\new@ifnextchar
\left\lbrace
\def\arraystretch{1.2}%
\array{@{}l@{\quad}l@{}}%
}
\ifx \env@cases\@tempa % add a bit of space after brace in amsmath cases env
\def\env@cases{%
\let\@ifnextchar\new@ifnextchar
\left\lbrace\hskip 2\p@
\def\arraystretch{1.2}%
\array{@{}l@{\quad}l@{}}%
}
\fi
}% end amsmath branch
\def\numc@left{\@centering}
\def\numc@opts{\dimen@ii\displaywidth}
\def\numc@forcenumwid{\numc@numwid}
\DeclareOption{subnum}{%
\let\numc@setsub\numc@subequations
\let\numc@resetsub\endsubequations
}
\DeclareOption{fleqn}{
\let\numc@left\mathindent
\def\numc@opts{\displaywidth\linewidth
\dimen@ii\linewidth }
}
\DeclareOption{leqno}{
\let\numc@forcenumwid\z@
}
\let\numc@expstyle\@empty
\let\numc@dispstyle\displaystyle
\DeclareOption{amsstyle}{
\def\numc@expstyle{$}% used in pairs for math-mode ($) explanation
\let\numc@dispstyle\textstyle
}
\DeclareOption{casesstyle}{
\newcommand\@unnc@casecr[1][\z@skip]{%
\cr \noalign{\vskip #1}%
}
\renewenvironment{cases}{%
\let\@ifnextchar\new@ifnextchar
\left\lbrace\hskip 2\p@
\vcenter to1.3em{}%
\vcenter\bgroup
\let\\\@unnc@casecr
\openup\jot
\tabskip\z@skip
\halign \bgroup
$\numc@dispstyle ##\m@th$\hfil
&\numc@expstyle\quad ##\unskip\numc@expstyle\hfil % \unskip removes space if no explanations
\cr
}{%
\crcr
\egroup
\egroup
\right.\n@space
}
}
\DeclareOption{cases}{\ExecuteOptions{casesstyle}}
\ProcessOptions
\endinput
% Send problem reports to asnd@triumf.ca
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