Package etomica.math.discrete

Class PermutationDegenerateIterator

java.lang.Object

etomica.math.discrete.PermutationDegenerateIterator

All Implemented Interfaces:

IndexIterator, java.io.Serializable

public class PermutationDegenerateIterator
extends java.lang.Object
implements IndexIterator, java.io.Serializable

Iterator that returns unique permutations of an array of integers, with degeneracy such that some of the integers may appear more than once in the array. Size of array is declared at construction. The setDegeneracy method then describes the number of degenerate elements that should be present in each iterate. For example, if constructed with n = 5 and the degeneracy is {2,3}, then successive calls to next() return the arrays:
{1,1,1,0,0}
{1,1,0,1,0}
{1,0,1,1,0}
{0,1,1,1,0}
{1,1,0,0,1}
{1,0,1,0,1}
{0,1,1,0,1}
{1,0,0,1,1}
{0,1,0,1,1}
{0,0,1,1,1}
The total number of iterates returned equals n!/product{degeneracy[i]!}

See Also:

Serialized Form

Constructor Summary

Constructors

Constructor	Description
PermutationDegenerateIterator(int n)	Constructs instance whose iterates are int[] of length n.

Method Summary

Modifier and Type	Method	Description
int	getD()
int[]	getDegeneracy()
boolean	hasNext()
static void	main(java.lang.String[] args)
int[]	next()	Returns the next iterate, or null if hasNext is false.
void	reset()	Readies the iterator for iteration.
void	setDegeneracy(int[] degeneracy)	Invokes setDegeneracy(degeneracy, degeneracy.length), thus using all elements of given array.
void	setDegeneracy(int[] degeneracy, int length)	Sets parameter that describes number of duplicate elements in the iterates.

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Constructor Detail

PermutationDegenerateIterator

public PermutationDegenerateIterator(int n)

Constructs instance whose iterates are int[] of length n. Default degeneracy is defined to have no repeated elements. User must call reset() before starting iteration.

Method Detail

setDegeneracy

public void setDegeneracy(int[] degeneracy)

Invokes setDegeneracy(degeneracy, degeneracy.length), thus using all elements of given array.

setDegeneracy

public void setDegeneracy(int[] degeneracy,
                          int length)

Sets parameter that describes number of duplicate elements in the iterates. For example, if degeneracy is {1,3,2}, then each iterate will have 1 element that is 0 (because degeneracy[0]=1), 3 elements that are 1 (because degeneracy[1] = 3), and 2 elements that are 2 (because degeneracy[2] = 2). Thus the array {1,0,1,2,2,1} would for this example be one of the iterates eventually returned by next(). Must be followed by a call to reset() before this method has any effect. Degeneracy is taken as the first "length" elements of the given array. Any elements degeneracy[i] for i>=length are ignored.

Throws:

java.lang.IllegalArgumentException - if the sum of the elements in degeneracy is not equal to the value of n set a construction.

getDegeneracy

public int[] getDegeneracy()

reset

public void reset()

Readies the iterator for iteration. Must be called after any calls to setDegeneracy.

Specified by:

reset in interface IndexIterator

hasNext

public boolean hasNext()

Specified by:

hasNext in interface IndexIterator

next

public int[] next()

Returns the next iterate, or null if hasNext is false.

Specified by:

next in interface IndexIterator

getD

public int getD()

Specified by:

getD in interface IndexIterator

main

public static void main(java.lang.String[] args)