org.openscience.cdk.group

Class Permutation

java.lang.Object

org.openscience.cdk.group.Permutation

public final class Permutation
extends Object

A permutation with some associated methods to multiply, invert, and convert to cycle strings. Much of the code in this was implemented from the C.A.G.E.S. book [Kreher, Donald and Stinson, Douglas, Combinatorial Algorithms Generation Enumeration and Search, 1998, CRC Press].

Author:

maclean

Belongs to CDK module:

group

Constructor Summary

Constructors

Constructor and Description
Permutation(int... values) Make a permutation from a set of values such that p[i] = x for the value x at position i.
Permutation(int size) Constructs an identity permutation with size elements.
Permutation(Permutation other) Construct a permutation from another one by cloning the values.

Method Summary

Methods

Modifier and Type	Method and Description
boolean	equals(Object other)
int	firstIndexOfDifference(Permutation other) Find an r such that this[r] != other[r].
int	get(int index) Get the value at this index.
List<Integer>	getOrbit(int element) Get all the elements in the same orbit in the permutation (unsorted).
int[]	getValues() Get all the values as an array.
int	hashCode()
Permutation	invert() Invert the permutation, so that for all i : inv[p[i]] = i.
boolean	isIdentity() Check to see if this permutation is the identity permutation.
Permutation	multiply(Permutation other) Multiply this permutation by another such that for all i, this[i] = this[other[i]].
void	set(int index, int value) Set the value at the specified index.
void	setTo(Permutation other) Alter a permutation by setting it to the values in the other permutation.
int	size() Get the number of elements in the permutation.
String	toCycleString() An easily-readable version of the permutation as a product of cycles.
String	toString()

Methods inherited from class java.lang.Object

clone, finalize, getClass, notify, notifyAll, wait, wait, wait

Constructor Detail

Permutation

public Permutation(int size)

Constructs an identity permutation with size elements.

Parameters:

size - the number of elements in the permutation

Permutation

public Permutation(int... values)

Make a permutation from a set of values such that p[i] = x for the value x at position i.

Parameters:

values - the elements of the permutation

Permutation

public Permutation(Permutation other)

Construct a permutation from another one by cloning the values.

Parameters:

other - the other permutation

Method Detail

equals

public boolean equals(Object other)

Overrides:

equals in class Object

hashCode

public int hashCode()

Overrides:

hashCode in class Object

isIdentity

public boolean isIdentity()

Check to see if this permutation is the identity permutation.

Returns:

true if for all i, p[i] = i

size

public int size()

Get the number of elements in the permutation.

Returns:

the number of elements

get

public int get(int index)

Get the value at this index.

Parameters:

index - the permutation value at this index.

Returns:

the value at this index

getValues

public int[] getValues()

Get all the values as an array.

Returns:

the values of the permutation

firstIndexOfDifference

public int firstIndexOfDifference(Permutation other)

Find an r such that this[r] != other[r].

Parameters:

other - the other permutation to compare with

Returns:

the first point at which the two permutations differ

getOrbit

public List<Integer> getOrbit(int element)

Get all the elements in the same orbit in the permutation (unsorted).

Parameters:

element - any element in the orbit

Returns:

the list of elements reachable in this permutation

set

public void set(int index,
       int value)

Set the value at the specified index.

Parameters:

index - the index to set the value

value - the value to set at this index

setTo

public void setTo(Permutation other)

Alter a permutation by setting it to the values in the other permutation.

Parameters:

other - the other permutation to use

Throws:

IllegalArgumentException - thrown if the permutations are of different size

multiply

public Permutation multiply(Permutation other)

Multiply this permutation by another such that for all i, this[i] = this[other[i]].

Parameters:

other - the other permutation to use

Returns:

a new permutation with the result of multiplying the permutations

invert

public Permutation invert()

Invert the permutation, so that for all i : inv[p[i]] = i.

Returns:

the inverse of this permutation

toCycleString

public String toCycleString()

An easily-readable version of the permutation as a product of cycles.

Returns:

the cycle form of the permutation as a string

toString

public String toString()

Overrides:

toString in class Object