Module org.cicirello.jpt

Package org.cicirello.permutations.distance

Class WeightedKendallTauDistance

java.lang.Object

org.cicirello.permutations.distance.WeightedKendallTauDistance

All Implemented Interfaces:

NormalizedPermutationDistanceMeasurerDouble, PermutationDistanceMeasurerDouble

public final class WeightedKendallTauDistance
extends Object
implements NormalizedPermutationDistanceMeasurerDouble

This class implements the weighted Kendall tau distance. In the original Kendall tau distance, each inverted pair of elements (i.e., such that element x appears someplace before y in Permutation p1, but someplace after y in Permutation p2) contributes 1 to the distance. Thus, since there are n(n-1)/2 pairs of elements, the maximum of Kendall tau distance is n(n-1)/2 where n is the permutation length. In this weighted Kendall tau distance, each element x of the permutation has an associated weight w(x), and each inverted pair x, y (where x appears before sometime prior to y in p1, but sometime after y in p2) contributes w(x) * w(y) to the weighted Kendall tau distance.

The weighted Kendall tau distance was first described in:
"Failure proximity: a fault localization-based approach" (Liu and Han, SIGSOFT 2006, pages 46-56).

The runtime of JPT's implementation is O(n lg n), where n is the permutation length. This runtime is achieved using a modified version of mergesort to sum the weighted inversions.

Constructor Summary

Constructors

Constructor	Description
WeightedKendallTauDistance(double[] weights)	Constructs an instance of the WeightedKendallTauDistance.

Method Summary

Modifier and Type	Method	Description
double	distancef(Permutation p1, Permutation p2)	Measures the distance between two permutations
double	maxf(int length)	Computes the maximum possible distance between permutations of a specified length.
int	supportedLength()	Gets the length of permutations supported by this instance of WeightedKendallTauDistance, which is equal to the length of the array of weights passed to the constructor.

Methods inherited from class java.lang.Object

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

Methods inherited from interface org.cicirello.permutations.distance.NormalizedPermutationDistanceMeasurerDouble

normalizedDistance

Constructor Detail

WeightedKendallTauDistance

public WeightedKendallTauDistance(double[] weights)

Constructs an instance of the WeightedKendallTauDistance.

Parameters:

weights - An array of weights, such that weights[e] is the weight of element e.

Method Detail

supportedLength

public int supportedLength()

Gets the length of permutations supported by this instance of WeightedKendallTauDistance, which is equal to the length of the array of weights passed to the constructor.

Returns:

The length of supported Permutations.

distancef

public double distancef(Permutation p1,
                        Permutation p2)

Measures the distance between two permutations

Specified by:

distancef in interface PermutationDistanceMeasurerDouble

Parameters:

p1 - first permutation

p2 - second permutation

Returns:

distance between p1 and p2

Throws:

IllegalArgumentException - if p1.length() is not equal to supportedLength(), or if p2.length() is not equal to supportedLength().

maxf

public double maxf(int length)

Computes the maximum possible distance between permutations of a specified length.

This implementation ignores the length parameter since this distance is configured for one specific length based upon the weights passed during construction.

Specified by:

maxf in interface NormalizedPermutationDistanceMeasurerDouble

Parameters:

length - Permutation length.

Returns:

the maximum distance between a pair of permutations of the specified length.