`array`

Synopsis:

\begin{array}{cols}column 1 entry&column 2 entry... &column n entry\\ ... \end{array}

or:

\begin{array}[pos]{cols}column 1 entry&column 2 entry... &column n entry\\ ... \end{array}

Produce a mathematical array. This environment can only be used in math
mode (see Modes), and normally appears within a displayed
mathematics environment such as `equation`

(see `equation`

).
Inside of each row the column entries are separated by an ampersand,
(`&`

). Rows are terminated with double-backslashes (see `\\`

).

This example shows a three by three array.

\begin{equation*} \chi(x) = \left| % vertical bar fence \begin{array}{ccc} x-a &-b &-c \\ -d &x-e &-f \\ -g &-h &x-i \end{array} \right| \end{equation*}

The required argument `cols` describes the number of columns, their
alignment, and the formatting of the intercolumn regions. For instance,
`\begin{array}{rcl}...\end{array}`

gives three columns: the
first flush right, the second centered, and the third flush left. See
`tabular`

for the complete description of `cols` and of the
other common features of the two environments, including the optional
`pos` argument.

There are two ways that `array`

diverges from `tabular`

. The
first is that `array`

entries are typeset in math mode, in
textstyle (see Math styles) except if the `cols` definition specifies
the column with `p{...}`

, which causes the entry to be typeset in
text mode. The second is that, instead of `tabular`

’s parameter
`\tabcolsep`

, LaTeX’s intercolumn space in an `array`

is
governed by
`\arraycolsep`

, which gives half the width between columns. The
default for this is ‘`5pt`’ so that between two columns comes
10pt of space.

To obtain arrays with braces the standard is to use the `amsmath`

package. It comes with environments `pmatrix`

for an array
surrounded by parentheses `(...)`

, `bmatrix`

for an array
surrounded by square brackets `[...]`

, `Bmatrix`

for an
array surrounded by curly braces `{...}`

, `vmatrix`

for
an array surrounded by vertical bars `|...|`

, and
`Vmatrix`

for an array surrounded by double vertical
bars `||...||`

, along with a number of other array constructs.

The next example uses the `amsmath`

package.

\usepackage{amsmath} % in preamble \begin{equation} \begin{vmatrix}{cc} % array with vert lines a &b \\ c &d \end{vmatrix}=ad-bc \end{equation}

There are many packages concerning arrays. The `array`

package has
many useful extensions, including more column types. The `dcolumn`

package adds a column type to center on a decimal point. For both see
the documentation on CTAN.