##

9.4.10 Arrays

Mathematical structures such as matrices and vectors require elements
to be arranged in rows and columns. Just as we can align material in
rows and columns in text mode using the
`tabular` environment (§4.6. Aligning Material in Rows and Columns), we can do the
same in maths mode using the `array` environment. The
`array` environment has the same format as the
`tabular` environment, however it must be in maths mode.
The column half-gaps are given by the length register
`\arraycolsep`

(analogous to `\tabcolsep`

).

**Example:**

**Example (Adding Delimiters):**

**Adding a Vertical Rule:**

A vertical rule can be added using `|` in the column
specifier. For example:

**Example (Cases):**

This example uses an invisible delimiter:

`amsmath`

`cases`environment:

The `amsmath` package provides some convenient environments to
typeset matrices: `pmatrix`, `bmatrix`,
`Bmatrix`, `vmatrix` and `Vmatrix`. These
are similar to the `array` environment except there is no
argument, and they add (respectively)
,
,
,
and
delimiters. There is also the
`matrix` environment that doesn't have any delimiters.

**Example:**

The `amsmath` package also provides the environment
`smallmatrix` designed for in-line use. You need to add any
delimiters explicitly.

**Example:**

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