Newsgroup: it.comp.software.tex
Titolo: Sistema in cui ogni equazione e' numerata

Ciao a tutti,
leggendo un forum in francese mi sono imbattuta in questo post cui nessuno
sa dare la risposta.
In pratica si vuole scrivere qualcosa del tipo
A = grande parentesi graffa che racchiude un sistema di cinque equazioni
ciascuna numerata.
Ora io so scrivere con eqnarray e varianti (align...) un insieme di n
equazioni numerate, ma non so come mettere la parentesi graffa che li
contenga, oppure so scrivere tutto correttamente con array o cases e \left\{
ma non so mettere i numeri a ciascuna equazione. Mi e' venuta l'idea di
guardare come il pacchetto amsmath definisce l'ambiente align e farne uno
analogo che pero' accetta un parametro e aggiunge una parentesi graffa prima
delle equazioni ma non saprei come fare.
Ora, non e' un problema urgente per me ma... qualcuno ha un'idea? (non ci
dormo la notte )
Grazie
--------------------------------
Inviato via 
http://arianna.libero.it/usenet/


Ho postato lo stesso probelma sul NG francese ed ecco la risposta (a naso
doveva essere facile ma proprio non ne uscivo da sola):
pacchetto cases con i suoi environnement numcases e subnumcases
Dal file .sty:
% C A S E S . S T Y ver 2.5 May 2002
%
% Copyright (C) 1993,1994,1995,2000,2002 by Donald Arseneau
% 
as...@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.
%
% 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.
%
% To use this package,
% include "\usepackage{cases}" after \documentclass. You may also
% specify "\usepackage[subnum]{cases}" to force *all* numcases
% environments to be treated as subnumcases.
%
% Question: Is there a {numcases*} environment for unnumbered cases?
% Answer: There is a {cases} environment in AMS-LaTeX, but it is just as
% convenient to stick with the canonical LaTeX array:
% \[ left side = \left\{ \begin{array}...\end{array} \right. \]
%
% Speaking of AMS-math, they use an entirely different system of equation
% numbering, and this package uses ordinary LaTeX numbering.
%
% - - - - -
% A simple example is:
% \begin{numcases}{|x|=}
% x, & for $x \geq 0$\\
% -x, & for $x < 0$
% \end{numcases}
%
% Giving:
% / x for x > 0 (1)
% |x| = < -
% \ -x for x < 0 (2)
%
% - - - - -
%
% 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}
