\documentclass[a4paper]{article}
\usepackage{amsmath,amsthm}

\newcommand{\fn}[1]{\texttt{#1}}
\newcommand{\cn}[1]{\texttt{\char92 #1}}

\title{Alignment of formulas}
\author{Richard Kaye\\School of Mathematics and Statistics\\
The University of Birmingham\\Birmingham B15 2TT\\U.K.}% If you
% change the document in any way, put your own name here instead of mine
\date{12th August 1998}

\begin{document}

\maketitle

\section{Introduction}

One of the most difficult aspects of typesetting mathematics is
splitting long formulas across several lines and aligning a group
of formulas.  Many of these aspects cannot be done automatically,
and it is up to you to control how this is to done. In all cases,
your judgement should be based on making the formula as readable
as possible.

Some control is available using \LaTeX's \fn{eqnarray} and
\fn{eqnarray*} environments.  However, this command is rather
limited for many applications and if you are creating a new
document in which you envisage a large number of long formulas or
equations I strongly recommend you use the AMS packages that are
available.

\section{Using the package}

Unless you are using one of the AMS's own class files, you load
the package by the command \cn{usepackage}\verb|{amsmath}|.  This
loads lots of useful new commands, including the alignment
environments referred to earlier. These are:
\begin{enumerate}
\item \fn{equation} essentially as usual \item \fn{multline} for
single equations or formulas going over two or more lines \item
\fn{split} as for multline, but with extra control over alignment
\item \fn{gather} for several equations grouped together \item
\fn{align} for several equations grouped together, with alignment
\item \fn{alignat} similar to align but with some extra alignment
features
\end{enumerate}

In most cases, there are starred and unstarred versions of
these---the starred versions do not produce any numbering
automatically.  There are a few other related commands, such as:
the \cn{intertext} command which interpolates text without messing
up the alignment; the \fn{subequations} environment which numbers
a groups of equations as \textit{5a}, \textit{5b}, \textit{5c},
etc.; the \fn{cases} environment for definitions by cases, and a
few other useful things.  I'm not going to describe in detail how
these commands ae used---you can get that from the documentation.
Instead, the next section contains some examples and you can
quickly get started by comparing the output with the \LaTeX\
source, which is called \fn{align.tex} and can be obtained from
the usual directory.

\section{Examples}

Many of these examples are directly taken from the documentation
of AMS\LaTeX, which is recommended reading if further details are
required.

Use of \fn{equation*}:
\begin{equation*}
a=b
\end{equation*}
Use of \fn{equation}:
\begin{equation}
a=b
\end{equation}
Use of \fn{split} and \fn{equation}:
\begin{equation}\label{xx}
\begin{split}
a& =b+c-d\\
 & \quad +e-f\\
 & =g+h\\
 & =i
\end{split}
\end{equation}
Use of \fn{multline}:
\begin{multline}
a+b+c+d+e+f+b+c+d+e+f+b+c+d+e+f\\
+b+c+d+e+f+b+c+d+e+f+i+j+k+l+m+n
\end{multline}
Use of \fn{gather}:
\begin{gather}
a_1=b_1+c_1\\
a_2=b_2+c_2-d_2+e_2 \label{eq:D}
\end{gather}
Use of \fn{align}:
\begin{align}
a_1& =b_1+c_1\\
a_2& =b_2+c_2-d_2+e_2
\end{align}
Other uses for \fn{align}:
\begin{align}
a_{11}& =b_{11}&
  a_{12}& =b_{12}\\
a_{21}& =b_{21}&
  a_{22}& =b_{22}+c_{22}
\end{align}
Use of \fn{flalign*}:
\begin{flalign*}
a_{11}& =b_{11}&
  a_{12}& =b_{12}\\
a_{21}& =b_{21}&
  a_{22}& =b_{22}+c_{22}
\end{flalign*}
Use of \cn{equation} and \cn{split}:
\begin{equation}\label{e:barwq}\begin{split}
H_c&=\frac{1}{2n} \sum^n_{l=0}(-1)^{l}(n-{l})^{p-2}
\sum_{l _1+\dots+ l _p=l}\prod^p_{i=1} \binom{n_i}{l _i}\\
&\quad\cdot[(n-l )-(n_i-l _i)]^{n_i-l _i}\cdot \Bigl[(n-l
)^2-\sum^p_{j=1}(n_i-l _i)^2\Bigr].
\end{split}\end{equation}
Use of \cn{align} to align textual annotations:
\begin{align}
x& = y_1-y_2+y_3-y_5+y_8-\dots
                    && \text{by \eqref{eq:C}}\\
 & = y'\circ y^*    && \text{by \eqref{eq:D}}\\
 & = y(0) y'        && \text {by Axiom 1.}
\end{align}
Use of \cn{aligned} to control placement of inner alignments:
\begin{equation*}
\begin{aligned}
\alpha&=\alpha\alpha\\
\beta&=\beta\beta\beta\beta\beta\\
\gamma&=\gamma
\end{aligned}
\qquad\text{versus}\qquad
\begin{aligned}[t]
\delta&=\delta\delta\\
\eta&=\eta\eta\eta\eta\eta\eta\\
\varphi&=\varphi
\end{aligned}
\end{equation*}
``Cases'' constructions:
\begin{equation}\label{eq:C}
P_{r-j}=
  \begin{cases}
    0&  \text{if $r-j$ is odd},\\
    r!\,(-1)^{(r-j)/2}&  \text{if $r-j$ is even}.
  \end{cases}
\end{equation}
Use of \cn{smash} and \cn{vphantom} to control vertical size:
\newcommand\ip[2]{\langle #1 \/ | #2 \/\rangle}
\newcommand\Ip[2]{\left\langle{\arraycolsep=0pt %
         \begin{array}{c|c}#1\/\,&\,#2\/\end{array}}%
         \right\rangle}
\newcommand\Ipd[2]{\left\langle{\arraycolsep=0pt %
         \begin{array}{c|c}\displaystyle#1\/\,&\,\displaystyle#2\/\end{array}}%
         \right\rangle}
\newcommand\conj[1]{\overline{#1}}
\begin{align*}
\Ipd{ u\: }{\: \smash{\sum_{i=1}^n F(e_i,v) e_i }\vphantom{\sum}}
&= \sum_{i=1}^n F(e_i,v) \ip{ u }{ e_i } \\
&= \sum_{i=1}^n \ip{ u }{ e_i } F(e_i,v) \\
&= \sum_{i=1}^n \conj{\ip{ e_i }{ u }} F(e_i,v) \\
&= F \biggl( \sum_{i=1}^n \ip{ e_i }{ u } e_i,v\biggr) = F( u, v
),
\end{align*}
(Note that without \cn{phantom} and \cn{smash} the brackets would
be too big because of the limits on the summations.) \cn{phantom}
is also useful if you are splitting a long equation over two lines
and you want a large left bracket on one line to match a large
right bracket on the next:
\begin{align*}
x&= \frac{1}{2} \left(\smash{\sum_{i=1}^n F(e_i,v) e_i
}\vphantom{\sum}+
\smash{\sum_{i=1}^n G(e_i,v) e_i} +\smash{\sum_{i=1}^n H(e_i,v) e_i }\vphantom{\sum}+\right.\\[8pt]
&\phantom{=}\qquad\left.\smash{\sum_{i=1}^n I(e_i,v) e_i
}\vphantom{\sum}+ \smash{\sum_{i=1}^n K(e_i,v) e_i} +
\smash{\sum_{i=1}^n J(e_i,v) e_i}\vphantom{\sum}\right)
\end{align*}
(Note also the adjustment to the vertical spacing in this
example.)

Use of \cn{intertext}:
\begin{proof} (a) Given $\mathbf v$, we have
\begin{align*}
1\,\mathbf v &= (-1)(-1)\mathbf v \\
&=(-1)(-1)\mathbf v +\mathbf 0  \\
&=(-1)(-1)\mathbf v + (\mathbf v + (-1)\mathbf v) \\
&=(-1)(-1)\mathbf v + ((-1)\mathbf v + \mathbf v) \\
&=((-1)(-1)\mathbf v + (-1)\mathbf v) + \mathbf v \\
&= \mathbf 0+\mathbf v \\
&= \mathbf v. \\
\intertext{(b) Again,}
0\,\mathbf v &= (1+(-1))\mathbf v \\
&= 1\mathbf v+(-1)\mathbf v\\
&= \mathbf v+(-1)\mathbf v \\
&= \mathbf 0.\\
\intertext{For (c),}
\lambda \mathbf 0 &= \lambda(\mathbf 0 + (-1)\mathbf 0) \\
&= \lambda \mathbf 0 + \lambda((-1)\mathbf 0) \\
&= \lambda \mathbf 0 + (-1)(\lambda \mathbf 0) \\
&=\mathbf 0
\end{align*}
as required
\end{proof}\begin{center}
\section{ACA ESTA EL LISTADO QUE GENERO EL ANTERIOR
DOCUMENTO}\end{center}


\begin{verbatim}

\documentclass[a4paper]{article}
\usepackage{amsmath,amsthm}

\newcommand{\fn}[1]{\texttt{#1}}
\newcommand{\cn}[1]{\texttt{\char92 #1}}

\title{Alignment of formulas}
\author{Richard Kaye\\School of Mathematics and Statistics\\
The University of Birmingham\\Birmingham B15 2TT\\U.K.}% If you
% change the document in any way, put your own name here instead of mine
\date{12th August 1998}

\begin{document}

\maketitle

\section{Introduction}

One of the most difficult aspects of typesetting mathematics is
splitting long formulas across several lines and aligning a group
of formulas.  Many of these aspects cannot be done automatically,
and it is up to you to control how this is to done. In all cases,
your judgement should be based on making the formula as readable
as possible.

Some control is available using \LaTeX's \fn{eqnarray} and
\fn{eqnarray*} environments.  However, this command is rather
limited for many applications and if you are creating a new
document in which you envisage a large number of long formulas or
equations I strongly recommend you use the AMS packages that are
available.

\section{Using the package}

Unless you are using one of the AMS's own class files, you load
the package by the command \cn{usepackage}\verb|{amsmath}|.  This
loads lots of useful new commands, including the alignment
environments referred to earlier. These are:
\begin{enumerate}
\item \fn{equation} essentially as usual \item \fn{multline} for
single equations or formulas going over two or more lines \item
\fn{split} as for multline, but with extra control over alignment
\item \fn{gather} for several equations grouped together \item
\fn{align} for several equations grouped together, with alignment
\item \fn{alignat} similar to align but with some extra alignment
features
\end{enumerate}

In most cases, there are starred and unstarred versions of
these---the starred versions do not produce any numbering
automatically.  There are a few other related commands, such as:
the \cn{intertext} command which interpolates text without messing
up the alignment; the \fn{subequations} environment which numbers
a groups of equations as \textit{5a}, \textit{5b}, \textit{5c},
etc.; the \fn{cases} environment for definitions by cases, and a
few other useful things.  I'm not going to describe in detail how
these commands ae used---you can get that from the documentation.
Instead, the next section contains some examples and you can
quickly get started by comparing the output with the \LaTeX\
source, which is called \fn{align.tex} and can be obtained from
the usual directory.

\section{Examples}

Many of these examples are directly taken from the documentation
of AMS\LaTeX, which is recommended reading if further details are
required.

Use of \fn{equation*}:
\begin{equation*}
a=b
\end{equation*}
Use of \fn{equation}:
\begin{equation}
a=b
\end{equation}
Use of \fn{split} and \fn{equation}:
\begin{equation}\label{xx}
\begin{split}
a& =b+c-d\\
 & \quad +e-f\\
 & =g+h\\
 & =i
\end{split}
\end{equation}
Use of \fn{multline}:
\begin{multline}
a+b+c+d+e+f+b+c+d+e+f+b+c+d+e+f\\
+b+c+d+e+f+b+c+d+e+f+i+j+k+l+m+n
\end{multline}
Use of \fn{gather}:
\begin{gather}
a_1=b_1+c_1\\
a_2=b_2+c_2-d_2+e_2 \label{eq:D}
\end{gather}
Use of \fn{align}:
\begin{align}
a_1& =b_1+c_1\\
a_2& =b_2+c_2-d_2+e_2
\end{align}
Other uses for \fn{align}:
\begin{align}
a_{11}& =b_{11}&
  a_{12}& =b_{12}\\
a_{21}& =b_{21}&
  a_{22}& =b_{22}+c_{22}
\end{align}
Use of \fn{flalign*}:
\begin{flalign*}
a_{11}& =b_{11}&
  a_{12}& =b_{12}\\
a_{21}& =b_{21}&
  a_{22}& =b_{22}+c_{22}
\end{flalign*}
Use of \cn{equation} and \cn{split}:
\begin{equation}\label{e:barwq}\begin{split}
H_c&=\frac{1}{2n} \sum^n_{l=0}(-1)^{l}(n-{l})^{p-2}
\sum_{l _1+\dots+ l _p=l}\prod^p_{i=1} \binom{n_i}{l _i}\\
&\quad\cdot[(n-l )-(n_i-l _i)]^{n_i-l _i}\cdot \Bigl[(n-l
)^2-\sum^p_{j=1}(n_i-l _i)^2\Bigr].
\end{split}\end{equation}
Use of \cn{align} to align textual annotations:
\begin{align}
x& = y_1-y_2+y_3-y_5+y_8-\dots
                    && \text{by \eqref{eq:C}}\\
 & = y'\circ y^*    && \text{by \eqref{eq:D}}\\
 & = y(0) y'        && \text {by Axiom 1.}
\end{align}
Use of \cn{aligned} to control placement of inner alignments:
\begin{equation*}
\begin{aligned}
\alpha&=\alpha\alpha\\
\beta&=\beta\beta\beta\beta\beta\\
\gamma&=\gamma
\end{aligned}
\qquad\text{versus}\qquad
\begin{aligned}[t]
\delta&=\delta\delta\\
\eta&=\eta\eta\eta\eta\eta\eta\\
\varphi&=\varphi
\end{aligned}
\end{equation*}
``Cases'' constructions:
\begin{equation}\label{eq:C}
P_{r-j}=
  \begin{cases}
    0&  \text{if $r-j$ is odd},\\
    r!\,(-1)^{(r-j)/2}&  \text{if $r-j$ is even}.
  \end{cases}
\end{equation}
Use of \cn{smash} and \cn{vphantom} to control vertical size:
\newcommand\ip[2]{\langle #1 \/ | #2 \/\rangle}
\newcommand\Ip[2]{\left\langle{\arraycolsep=0pt %
         \begin{array}{c|c}#1\/\,&\,#2\/\end{array}}%
         \right\rangle}
\newcommand\Ipd[2]{\left\langle{\arraycolsep=0pt %
         \begin{array}{c|c}\displaystyle#1\/\,&\,\displaystyle#2\/\end{array}}%
         \right\rangle}
\newcommand\conj[1]{\overline{#1}}
\begin{align*}
\Ipd{ u\: }{\: \smash{\sum_{i=1}^n F(e_i,v) e_i }\vphantom{\sum}}
&= \sum_{i=1}^n F(e_i,v) \ip{ u }{ e_i } \\
&= \sum_{i=1}^n \ip{ u }{ e_i } F(e_i,v) \\
&= \sum_{i=1}^n \conj{\ip{ e_i }{ u }} F(e_i,v) \\
&= F \biggl( \sum_{i=1}^n \ip{ e_i }{ u } e_i,v\biggr) = F( u, v
),
\end{align*}
(Note that without \cn{phantom} and \cn{smash} the brackets would
be too big because of the limits on the summations.) \cn{phantom}
is also useful if you are splitting a long equation over two lines
and you want a large left bracket on one line to match a large
right bracket on the next:
\begin{align*}
x&= \frac{1}{2} \left(\smash{\sum_{i=1}^n F(e_i,v) e_i
}\vphantom{\sum}+
\smash{\sum_{i=1}^n G(e_i,v) e_i} +\smash{\sum_{i=1}^n H(e_i,v) e_i }\vphantom{\sum}+\right.\\[8pt]
&\phantom{=}\qquad\left.\smash{\sum_{i=1}^n I(e_i,v) e_i
}\vphantom{\sum}+ \smash{\sum_{i=1}^n K(e_i,v) e_i} +
\smash{\sum_{i=1}^n J(e_i,v) e_i}\vphantom{\sum}\right)
\end{align*}
(Note also the adjustment to the vertical spacing in this
example.)

Use of \cn{intertext}:
\begin{proof} (a) Given $\mathbf v$, we have
\begin{align*}
1\,\mathbf v &= (-1)(-1)\mathbf v \\
&=(-1)(-1)\mathbf v +\mathbf 0  \\
&=(-1)(-1)\mathbf v + (\mathbf v + (-1)\mathbf v) \\
&=(-1)(-1)\mathbf v + ((-1)\mathbf v + \mathbf v) \\
&=((-1)(-1)\mathbf v + (-1)\mathbf v) + \mathbf v \\
&= \mathbf 0+\mathbf v \\
&= \mathbf v. \\
\intertext{(b) Again,}
0\,\mathbf v &= (1+(-1))\mathbf v \\
&= 1\mathbf v+(-1)\mathbf v\\
&= \mathbf v+(-1)\mathbf v \\
&= \mathbf 0.\\
\intertext{For (c),}
\lambda \mathbf 0 &= \lambda(\mathbf 0 + (-1)\mathbf 0) \\
&= \lambda \mathbf 0 + \lambda((-1)\mathbf 0) \\
&= \lambda \mathbf 0 + (-1)(\lambda \mathbf 0) \\
&=\mathbf 0
\end{align*}
as required.
\end{proof}

\end{document}

\end{verbatim}


\end{document}