An S4 class to represent a permutation order.

## Slots

`rows`

An `integer`

vector giving the rows permutation.

`columns`

An `integer`

vector giving the columns permutation.

`method`

A `character`

string indicating the seriation method used.

## Subset

In the code snippets below, `x`

is a `PermutationOrder`

object.

`x[[i]]`

Extracts information from a slot selected by subscript `i`

.
`i`

is a length-one `character`

vector. Returns the corresponding slot
values.