de.lmu.ifi.dbs.elki.distance.distancefunction
Class RandomStableDistanceFunction

java.lang.Object
  de.lmu.ifi.dbs.elki.distance.distancefunction.AbstractDBIDDistanceFunction<DoubleDistance>
      de.lmu.ifi.dbs.elki.distance.distancefunction.RandomStableDistanceFunction

All Implemented Interfaces:

DBIDDistanceFunction<DoubleDistance>, DistanceFunction<DBID,DoubleDistance>, InspectionUtilFrequentlyScanned, Parameterizable

public class RandomStableDistanceFunction
extends AbstractDBIDDistanceFunction<DoubleDistance>

This is a dummy distance providing random values (obviously not metrical), useful mostly for unit tests and baseline evaluations: obviously this distance provides no benefit whatsoever. This distance is based on the combined hash codes of the two objects queried, if they are different. Extra caution is done to ensure symmetry and objects with the same ID will have a distance of 0. Obviously this distance is not metrical.

Nested Class Summary

static class

RandomStableDistanceFunction.Parameterizer Parameterization class.

Field Summary

private long	seed Seed for reproducible random.
static RandomStableDistanceFunction	STATIC Static instance

Constructor Summary

RandomStableDistanceFunction(long seed)
Constructor.

Method Summary

DoubleDistance	distance(DBID o1, DBID o2) Returns the distance between the two objects specified by their object ids.
boolean	equals(Object obj)
DoubleDistance	getDistanceFactory() Method to get the distance functions factory.
int	hashCode()
private double	pseudoRandom(long seed, int input) Pseudo random number generator, adaption of the common rand48 generator which can be found in C (man drand48), Java and attributed to Donald Knuth.
String	toString()

Methods inherited from class de.lmu.ifi.dbs.elki.distance.distancefunction.AbstractDBIDDistanceFunction

getInputTypeRestriction, instantiate, isMetric, isSymmetric

Methods inherited from class java.lang.Object

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

Field Detail

STATIC

public static final RandomStableDistanceFunction STATIC

Static instance

seed

private long seed

Seed for reproducible random.

Constructor Detail

RandomStableDistanceFunction

public RandomStableDistanceFunction(long seed)

Constructor. Usually it is preferred to use the static instance!

Method Detail

distance

public DoubleDistance distance(DBID o1,
                               DBID o2)

Description copied from interface: DBIDDistanceFunction

Returns the distance between the two objects specified by their object ids.

Specified by:

distance in interface DBIDDistanceFunction<DoubleDistance>

Specified by:

distance in class AbstractDBIDDistanceFunction<DoubleDistance>

Parameters:

o1 - first object id

o2 - second object id

Returns:

the distance between the two objects specified by their object ids

pseudoRandom

private double pseudoRandom(long seed,
                            int input)

Pseudo random number generator, adaption of the common rand48 generator which can be found in C (man drand48), Java and attributed to Donald Knuth.

Parameters:

seed - Seed value

input - Input code

Returns:

Pseudo random double value

getDistanceFactory

public DoubleDistance getDistanceFactory()

Description copied from interface: DistanceFunction

Method to get the distance functions factory.

Specified by:

getDistanceFactory in interface DistanceFunction<DBID,DoubleDistance>

Specified by:

getDistanceFactory in class AbstractDBIDDistanceFunction<DoubleDistance>

Returns:

Factory for distance objects

toString

public String toString()

Overrides:

toString in class Object

equals

public boolean equals(Object obj)

Overrides:

equals in class Object

hashCode

public int hashCode()

Overrides:

hashCode in class Object