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

Class RandomStableDistanceFunction

java.lang.Object

de.lmu.ifi.dbs.elki.distance.distancefunction.AbstractDatabaseDistanceFunction<DBID>

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

All Implemented Interfaces:

DBIDDistanceFunction, DistanceFunction<DBID>

public class RandomStableDistanceFunction
extends AbstractDatabaseDistanceFunction<DBID>
implements DBIDDistanceFunction

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.

Author:

Erich Schubert

Nested Class Summary

Nested Classes

Modifier and Type	Class and Description
static class	RandomStableDistanceFunction.Parameterizer Parameterization class.

Nested classes/interfaces inherited from class de.lmu.ifi.dbs.elki.distance.distancefunction.AbstractDatabaseDistanceFunction

AbstractDatabaseDistanceFunction.Instance<O>

Field Summary

Fields

Modifier and Type	Field and Description
private long	seed Seed for reproducible random.
static RandomStableDistanceFunction	STATIC Static instance

Constructor Summary

Constructors

Constructor and Description
RandomStableDistanceFunction(long seed) Constructor.

Method Summary

Methods

Modifier and Type	Method and Description
double	distance(DBIDRef o1, DBIDRef o2) Returns the distance between the two objects specified by their object ids.
boolean	equals(Object obj)
TypeInformation	getInputTypeRestriction() Get the input data type of the function.
int	hashCode()
<T extends DBID> DistanceQuery<T>	instantiate(Relation<T> relation) Instantiate with a database to get the actual distance query.
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.AbstractDatabaseDistanceFunction

isMetric, isSymmetric

Methods inherited from class java.lang.Object

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

Methods inherited from interface de.lmu.ifi.dbs.elki.distance.distancefunction.DistanceFunction

isMetric, isSymmetric

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 double distance(DBIDRef o1,
              DBIDRef o2)

Description copied from interface: DBIDDistanceFunction

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

Specified by:

distance in interface DBIDDistanceFunction

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

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

getInputTypeRestriction

public TypeInformation getInputTypeRestriction()

Description copied from interface: DistanceFunction

Get the input data type of the function.

Specified by:

getInputTypeRestriction in interface DistanceFunction<DBID>

Returns:

Type restriction

instantiate

public <T extends DBID> DistanceQuery<T> instantiate(Relation<T> relation)

Description copied from interface: DistanceFunction

Instantiate with a database to get the actual distance query.

Specified by:

instantiate in interface DistanceFunction<DBID>

Parameters:

relation - The representation to use

Returns:

Actual distance query.