\documentclass[a4paper]{article}
\usepackage{easymat}%

\let\package\texttt % so \package{foo} comes out in \tt
\let\envname\textsf % so \envname{foo} comes out as \sf

\title{The package \package{easymat}}
\author{Enrico Bertolazzi\\\\
  Laboratorio di Matematica Applicata\\
  Dipartimento di Ingegneria Civile ed Ambientale\\
  Universit\`a degli Studi di Trento\\
  Mesiano, Trento, Italy\\\\
  \texttt{bertolaz@ing.unitn.it}}

\date{}

\begin{document}
\maketitle
\begin{abstract}
The \package{easymat} package is 
a macro package for writing block matrices, with various
kinds of rules~(lines) between rows or columns, and
uses an array/tabular-like syntax. 
\end{abstract}


\section{Some examples with \package{easymat}}
This package was inspired by the package \package{pmat}, version~0.1,
of Tom\'as Oliveira~e~Silva. This beautiful package allows easy
construction of partitioned matrices. Unfortunately, at least this 
version, the package is not reentrant, so you cannot build 
block matrices which contain more block matrices. I have solved this problem 
writing a similar package with different features (some things
have been added and some others avoided), however, the algorithms are
essentially the same as those of \package{pmat}.

Load the package in the usual way:
\begin{verbatim}
   \documentclass{article}
   .
   .
   \usepackage[thinlines,thiklines]{easymat}
   .
   .
\end{verbatim}
The options \texttt{thinlines}, and \texttt{thiklines} are self explanatory.
\package{easymat} provides the \envname{MAT}~environment which is a
simple re-implementation of the
array/tabular environment, with some limitation and some additional features.
The syntax is
\begin{verbatim}
   \begin{MAT}`[3pt]'`{ccl:c}'
      a & b & ... & n \\`[2mm]'`;'
   .
   \end{MAT}
\end{verbatim}
where \verb+`[3pt]'+ is an optional spacing between row and columns,
\verb+`{ccl:c}'+ is the definition of the column (like tabular or array),
\verb+`[2mm]'+ is an optional spacing argument for the row, `;' is an optional 
definition of the row rule.
The main feature of the \envname{MAT}~environment
is that it is reentrant:

\begin{verbatim}
\[ \left[\begin{MAT}{cc}
     1 & 2 \\
     3 & \left(\begin{MAT}{cc}
              a & b \\
              c & d
         \end{MAT}\right)
   \end{MAT}\right]
\]
\end{verbatim}
which produces
\[ \left[\begin{MAT}{cc}
     1 & 2 \\
     3 & \left(\begin{MAT}{cc}
              a & b \\
              c & d
         \end{MAT}\right)
   \end{MAT}\right]
\]
As in \envname{tabular} or \envname{array}
it is possible to define columns as
rules or dashes:
\begin{verbatim}
\[  \begin{MAT}{|c:c;rl}
         1 & b & c & f\\
         1 & 2 & 3 & h\\
         1 & b & csssss & \\
         1 & b & c & \frac{1}{2} \\
         A & B & C & d
   \end{MAT}
\]
\end{verbatim}
produces
\[  \begin{MAT}{|c:c;rl}
         1 & b & c & f\\
         1 & 2 & 3 & h\\
         1 & b & csssss & \\
         1 & b & c & \frac{1}{2} \\
         A & B & C & d
   \end{MAT}
\]
\texttt r,~\texttt c,~\texttt l~mean ``right'', ``center'', and ``left'' 
alignment. The available rules for the columns are
\begin{center}
\begin{tabular}{|l|l|}
\hline
nothing  & no rule \\
\verb+|+ & solid line \\
\verb+:+ & dash line \\
\verb+;+ & dot-dash line \\
\verb+,+ & dotted line \\
\hline
\end{tabular}
\end{center}
The lines are ended by \verb+\\+ for which we can use \verb+[ ]+ as
an optional argument for spacing and an optional character for the 
definition of a rule. The character codes are the following
\begin{center}
\begin{tabular}{|l|l|}
\hline
nothing  & no rule \\
\verb+-+ & solid line \\
\verb+:+ & dash line \\
\verb+;+ & dot-dash line \\
\verb+,+ & dotted line \\
\hline
\end{tabular}
\end{center}
In order to avoid bad alignment for the first (empty) and the last
line is better to use the commands \verb+\first+ and \verb+\last+
instead of \verb+\\+. The following example shows some
of the features
\begin{verbatim}
\[
 A=\left(\begin{MAT}{|c;c;c|}
         \first:
         1 & b & c \\;
         1 & \begin{MAT}[0pt]{|l:l|}
                \first -11 & 12 \\:
                13 \last-
             \end{MAT} & c \\-
         1 & b & csssss \\:
         1 & b & c \\;
         A & B & C
         \last-
    \end{MAT}\right)
\]
\end{verbatim}
\[
 A=\left(\begin{MAT}{|c;c;c|}
         \first:
         1 & b & c \\;
         1 & \begin{MAT}[0pt]{|l:l|}
                \first -11 & 12 \\:
                13 \last-
             \end{MAT} & c \\-
         1 & b & csssss \\:
         1 & b & c \\;
         A & B & C
         \last-
    \end{MAT}\right)
\]

This final example shows a slightly more complex (reentrant)
definition in 
which the \envname{MAT}~environment is used:
\begin{verbatim}
\def\recurse#1#2\end{%
   \if\noexpand#1-\def\next##1##2{}\else\let\next=\recursea\fi%
   \expandafter\next{#1}{#2}%
}%
\def\recursea#1#2{%
  \bgroup%
    \begin{MAT}{c;c|c}%
       \expandafter\recurse#2-\end &
        #1 &%
         \expandafter\recurse#2-\end \\-%
        #1 &%
         \expandafter\recurse#2-\end &%
          #1 \\;%
         \expandafter\recurse#2-\end &%
          #1 &%
           \expandafter\recurse#2-\end%
    \end{MAT}%
  \egroup%
}
\[ \recurse\clubsuit\diamondsuit\heartsuit\end \]
\end{verbatim}
\typeout{This example can take a while to compile on small machine, please wait...}
It produces the following output:
\def\recurse#1#2\end{%
   \if\noexpand#1-\def\next##1##2{}\else\let\next=\recursea\fi%
   \expandafter\next{#1}{#2}%
}%
\def\recursea#1#2{%
  \bgroup%
    \begin{MAT}{c;c|c}%
       \expandafter\recurse#2-\end &
        #1 &%
         \expandafter\recurse#2-\end \\-%
        #1 &%
         \expandafter\recurse#2-\end &%
          #1 \\;%
         \expandafter\recurse#2-\end &%
          #1 &%
           \expandafter\recurse#2-\end%
    \end{MAT}%
  \egroup%
}
\[ \recurse\clubsuit\diamondsuit\heartsuit\end \]
\typeout{...thanks, I have done}

\end{document}