% Copyright 2006 by Till Tantau
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% This file may be distributed and/or modified
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% 2. under the GNU Free Documentation License.
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\section{Matrix Library}

\begin{tikzlibrary}{matrix}
  This library packages defines additional styles and options for
  creating matrices.
\end{tikzlibrary}


\subsection{Matrices of Nodes}

A \emph{matrix of nodes} is a \tikzname\ matrix in which each cell
contains a node. In this case it is bothersome having to write
|\node{| at the beginning of each cell and |};| at the end of each
cell. The following key simplifies typesetting such matrices.

\begin{key}{/tikz/matrix of nodes}
  Conceptually, this key adds |\node{| at the beginning and |};| at
  the end of each cell and sets the |anchor| of the node to
  |base|. Furthermore, it adds  the option |name| option to each node,
  where the name is set to  \meta{matrix name}|-|\meta{row
    number}|-|\meta{column number}. For  example, if the matrix has
  the name |my matrix|, then the node in  the upper left cell will get
  the name |my matrix-1-1|.
\begin{codeexample}[]
\begin{tikzpicture}
  \matrix (magic) [matrix of nodes]
  {
    8 & 1 & 6 \\
    3 & 5 & 7 \\
    4 & 9 & 2 \\
  };

  \draw[thick,red,->] (magic-1-1) |- (magic-2-3);
\end{tikzpicture}
\end{codeexample}

  You may wish to add options to certain nodes in the matrix. This can
  be achieved in three ways.
  \begin{enumerate}
  \item You can modify, say, the
    |row 2 column 5| style to pass special options to this particular
    cell.

\begin{codeexample}[]
\begin{tikzpicture}[row 2 column 3/.style=red]
  \matrix [matrix of nodes]
  {
    8 & 1 & 6 \\
    3 & 5 & 7 \\
    4 & 9 & 2 \\
  };
\end{tikzpicture}
\end{codeexample}

  \item At the beginning of a cell, you can use a special syntax. If a
    cell starts with a vertical bar, then everything between this bar
    and the next bar is passed on to the |node| command.
{\catcode`\|=12
\begin{codeexample}[]
\begin{tikzpicture}
  \matrix [matrix of nodes]
  {
    8 & 1 &         6 \\
    3 & 5 & |[red]| 7 \\
    4 & 9 &         2 \\
  };
\end{tikzpicture}
\end{codeexample}
}
  You can also use an option like \verb!|[red] (seven)|! to give a
  different name to the node.

  Note that the |&| character also takes an optional argument, which
  is an extra column skip.
{\catcode`\|=12
\begin{codeexample}[]
\begin{tikzpicture}
  \matrix [matrix of nodes]
  {
    8 &[1cm] 1 &[3mm] |[red]| 6 \\
    3 &      5 &      |[red]| 7 \\
    4 &      9 &              2 \\
  };
\end{tikzpicture}
\end{codeexample}
}
  \item If your cell starts with a |\path| command or any command that
    expands to |\path|, which includes |\draw|, |\node|, |\fill| and
    others, the |\node{| startup code and the |};| code are
    suppressed. This means that for this particular cell you can
    provide a totally different contents.

\begin{codeexample}[]
\begin{tikzpicture}
  \matrix [matrix of nodes]
  {
    8 & 1 & 6 \\
    3 & 5 & \node[red]{7}; \draw(0,0) circle(10pt);\\
    4 & 9 & 2 \\
  };
\end{tikzpicture}
\end{codeexample}
  \end{enumerate}
\end{key}

\begin{key}{/tikz/matrix of math nodes}
  This style is almost the same as the previous style, only |$| is %$
  added at the beginning and at the end of each node, so math mode
  will be switched on in all nodes.
{\catcode`\|=12
\begin{codeexample}[]
\begin{tikzpicture}
  \matrix [matrix of math nodes]
  {
    a_8 & a_1 &         a_6 \\
    a_3 & a_5 & |[red]| a_7 \\
    a_4 & a_9 &         a_2 \\
  };
\end{tikzpicture}
\end{codeexample}
}
\end{key}

\begin{key}{/tikz/nodes in empty cells=\meta{true or false} (default true)}
  When set to |true|, a node (with an empty contents) is put in empty
  cells. Normally, empty cells are just, well, empty. The style can be
  used together with both a |matrix of nodes| and a
  |matrix of math nodes|.
\begin{codeexample}[]
\begin{tikzpicture}
  \matrix [matrix of math nodes,nodes={circle,draw}]
  {
    a_8 &     & a_6 \\
    a_3 &     & a_7 \\
    a_4 & a_9 &     \\
  };
\end{tikzpicture}
\end{codeexample}
\begin{codeexample}[]
\begin{tikzpicture}
  \matrix [matrix of math nodes,nodes={circle,draw},nodes in empty cells]
  {
    a_8 &     & a_6 \\
    a_3 &     & a_7 \\
    a_4 & a_9 &     \\
  };
\end{tikzpicture}
\end{codeexample}
\end{key}


\subsection{End-of-Lines and End-of-Row Characters in Matrices of Nodes}

Special care must be taken about the usage of the |\\| command inside
a matrix of nodes. The reason is that this character is overloaded in
\TeX: On the one hand, it is used to denote the end of a line in
normal text; on the other hand it is used to denote the end of a row
in a matrix. Now, if a matrix contains node which in turn may have
multiple lines, it is unclear which meaning of |\\| should be used.

This problem arises only when you use the |text width| option of
nodes. Suppose you write a line like
\begin{codeexample}[code only]
\matrix [text width=5cm,matrix of nodes]
{
  first row & upper line \\ lower line \\
  second row & hmm \\
};
\end{codeexample}
This leaves \TeX\ trying to riddle out how many rows this matrix
should have. Do you want two rows with the upper right cell containing
a two-line text. Or did you mean a three row matrix with the second
row having only one cell?

Since \TeX\ is not clairvoyant, the following rules are used:
\begin{enumerate}
\item Inside a matrix, the |\\| command, by default, signals the end
  of the row, not the end of a line in a cell.
\item However, there is an exception to this rule: If a cell
  starts with a \TeX-group (this is, with |{|), % }
  then inside this first group the |\\| command retains the meaning of
  ``end of line'' character. Note that this special rule works only
  for the first group in a cell and this group must be at the
  beginning.
\end{enumerate}

The net effect of these rules is the following: Normally, |\\| is an
end-of-row indicator; if you want to use it as an end-of-line
indicator in a cell, just put the whole cell in curly braces. The
following example illustrates the difference:
\begin{codeexample}[]
\begin{tikzpicture}
  \matrix [matrix of nodes,nodes={text width=16mm,draw}]
  {
    row 1 & upper line \\ lower line \\
    row 2 & hmm \\
  };
\end{tikzpicture}
\end{codeexample}
\begin{codeexample}[]
\begin{tikzpicture}
  \matrix [matrix of nodes,nodes={text width=16mm,draw}]
  {
    row 1 & {upper line \\ lower line} \\
    row 2 & hmm \\
  };
\end{tikzpicture}
\end{codeexample}

Note that this system is not fool-proof. If you write things like
|a&b{c\\d}\\| in a matrix of nodes, an error will result (because the
second cell did not start with a brace, so |\\| retained its normal
meaning and, thus, the second cell contained the text |b{c|, which is
not balanced with respect to the number of braces).

\subsection{Delimiters}

Delimiters are parentheses or braces to the left and right of a
formula or a matrix. The matrix library offers options for adding such
delimiters to a matrix. However, delimiters can actually be added to
any node that has the standard anchors |north|, |south|, |north west|
and so on. In particular, you can add delimiters to any |rectangle|
box. They are implemented by ``measuring the height'' of the node and
then adding a delimiter of the correct size to the left or right using
some after node magic.

\begin{key}{/tikz/left delimiter=\meta{delimiter}}
  This option can be given to a any node that has the standard anchors
  |north|, |south| and so on. The \meta{delimiter} can be any
  delimiter that is acceptable to \TeX's |\left| command.
\begin{codeexample}[]
\begin{tikzpicture}
  \matrix [matrix of math nodes,left delimiter=(,right delimiter=\}]
  {
    a_8 & a_1 & a_6 \\
    a_3 & a_5 & a_7 \\
    a_4 & a_9 & a_2 \\
  };
\end{tikzpicture}
\end{codeexample}

\begin{codeexample}[]
\begin{tikzpicture}
  \node [fill=red!20,left delimiter=(,right delimiter=\}]
    {$\displaystyle\int_0^1 x\,dx$};
\end{tikzpicture}
\end{codeexample}

  \begin{stylekey}{/tikz/every delimiter (initially \normalfont empty)}
    This style is executed for every delimiter. You can use it to shift
    or color delimiters or do whatever.
  \end{stylekey}

  \begin{stylekey}{/tikz/every left delimiter (initially \normalfont empty)}
    This style is additionally executed for every left delimiter.
\begin{codeexample}[]
\begin{tikzpicture}
  [every left delimiter/.style={red,xshift=1ex},
   every right delimiter/.style={xshift=-1ex}]
  \matrix [matrix of math nodes,left delimiter=(,right delimiter=\}]
  {
    a_8 & a_1 & a_6 \\
    a_3 & a_5 & a_7 \\
    a_4 & a_9 & a_2 \\
  };
\end{tikzpicture}
\end{codeexample}
  \end{stylekey}
\end{key}

\begin{key}{/tikz/right delimiter=\meta{delimiter}}
  Works as above.
  \begin{stylekey}{/tikz/every right delimiter (initially \normalfont empty)}
    Works as above.
  \end{stylekey}
\end{key}


\begin{key}{/tikz/above delimiter=\meta{delimiter}}
  This option allows you to add a delimiter above the node. It is
  implementing by rotating a left delimiter.
\begin{codeexample}[]
\begin{tikzpicture}
  \matrix [matrix of math nodes,%
           left delimiter=\|,right delimiter=\rmoustache,%
           above delimiter=(,below delimiter=\}]
  {
    a_8 & a_1 & a_6 \\
    a_3 & a_5 & a_7 \\
    a_4 & a_9 & a_2 \\
  };
\end{tikzpicture}
\end{codeexample}

  \begin{stylekey}{/tikz/every above delimiter (initially \normalfont empty)}
    Works as above.
  \end{stylekey}
\end{key}

\begin{key}{/tikz/below delimiter=\meta{delimiter}}
  Works as above.
  \begin{stylekey}{/tikz/every below delimiter (initially \normalfont empty)}
    Works as above.
  \end{stylekey}
\end{key}



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