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

Class ArcCosineUnitlengthDistanceFunction

java.lang.Object

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

All Implemented Interfaces:

DistanceFunction<NumberVector>, NumberVectorDistanceFunction<NumberVector>, PrimitiveDistanceFunction<NumberVector>, SpatialPrimitiveDistanceFunction<NumberVector>

public class ArcCosineUnitlengthDistanceFunction
extends java.lang.Object
implements SpatialPrimitiveDistanceFunction<NumberVector>, NumberVectorDistanceFunction<NumberVector>

Arcus cosine distance function for feature vectors.

The arc cosine distance is computed as the arcus from the cosine similarity value, i.e., arccos(<v1,v2>).

Cosine similarity is defined as \[ \tfrac{\vec{x}\cdot\vec{y}}{||a||\cdot||b||} =_{||a||=||b||=1} \vec{x}\cdot\vec{y} \] Arcus cosine distance then is \[ \operatorname{arccos} \tfrac{\vec{x}\cdot\vec{y}}{||a||\cdot||b||} =_{||a||=||b||=1} \operatorname{arccos} \vec{x}\cdot\vec{y} \in [0;\pi] \]

This implementation assumes that \(||a||=||b||=1\). If this does not hold for your data, use ArcCosineDistanceFunction instead!

CosineUnitlengthDistanceFunction is a bit less expensive, and will yield the same ranking of neighbors.

Since:

0.7.5

Author:

Erich Schubert

Nested Class Summary

Nested Classes

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

Field Summary

Fields

Modifier and Type	Field and Description
static ArcCosineUnitlengthDistanceFunction	STATIC Static instance

Constructor Summary

Constructors

Constructor and Description
ArcCosineUnitlengthDistanceFunction() Deprecated. Use static instance!

Method Summary

Modifier and Type	Method and Description
double	distance(NumberVector v1, NumberVector v2) Computes the cosine distance for two given feature vectors.
boolean	equals(java.lang.Object obj)
SimpleTypeInformation<? super NumberVector>	getInputTypeRestriction() Get the input data type of the function.
int	hashCode()
double	minDist(SpatialComparable mbr1, SpatialComparable mbr2) Computes the distance between the two given MBRs according to this distance function.
java.lang.String	toString()

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.SpatialPrimitiveDistanceFunction

instantiate

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

isMetric, isSquared, isSymmetric

Field Detail

STATIC

public static final ArcCosineUnitlengthDistanceFunction STATIC

Static instance

Constructor Detail

ArcCosineUnitlengthDistanceFunction

@Deprecated
public ArcCosineUnitlengthDistanceFunction()

Deprecated. Use static instance!

Constructor - use STATIC instead.

Method Detail

distance

public double distance(NumberVector v1,
                       NumberVector v2)

Computes the cosine distance for two given feature vectors.

The cosine distance is computed as the arcus from the cosine similarity value, i.e., arccos(<v1,v2>).

Specified by:

distance in interface NumberVectorDistanceFunction<NumberVector>

Specified by:

distance in interface PrimitiveDistanceFunction<NumberVector>

Parameters:

v1 - first feature vector

v2 - second feature vector

Returns:

the cosine distance for two given feature vectors v1 and v2

minDist

public double minDist(SpatialComparable mbr1,
                      SpatialComparable mbr2)

Description copied from interface: SpatialPrimitiveDistanceFunction

Computes the distance between the two given MBRs according to this distance function.

Specified by:

minDist in interface SpatialPrimitiveDistanceFunction<NumberVector>

Parameters:

mbr1 - the first MBR object

mbr2 - the second MBR object

Returns:

the distance between the two given MBRs according to this distance function

toString

public java.lang.String toString()

Overrides:

toString in class java.lang.Object

equals

public boolean equals(java.lang.Object obj)

Overrides:

equals in class java.lang.Object

hashCode

public int hashCode()

Overrides:

hashCode in class java.lang.Object

getInputTypeRestriction

public SimpleTypeInformation<? super NumberVector> getInputTypeRestriction()

Description copied from interface: DistanceFunction

Get the input data type of the function.

Specified by:

getInputTypeRestriction in interface DistanceFunction<NumberVector>

Specified by:

getInputTypeRestriction in interface PrimitiveDistanceFunction<NumberVector>

Returns:

Type restriction