array (LaTeX2e unofficial reference manual (November 2018))

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### 8.2 `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, 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 Modes) 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.

Unofficial LaTeX2e reference manual