Package elki.distance

Class ArcCosineUnitlengthDistance

java.lang.Object

elki.distance.ArcCosineUnitlengthDistance

All Implemented Interfaces:

Distance<NumberVector>, NumberVectorDistance<NumberVector>, PrimitiveDistance<NumberVector>, SpatialPrimitiveDistance<NumberVector>

public class ArcCosineUnitlengthDistance
extends java.lang.Object
implements SpatialPrimitiveDistance<NumberVector>, NumberVectorDistance<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 ArcCosineDistance instead!

CosineUnitlengthDistance and SqrtCosineUnitlengthDistance are a bit less expensive to compute, and will yield the same ranking of neighbors.

Since:

0.7.5

Author:

Erich Schubert

Nested Class Summary

Nested Classes

Modifier and Type	Class	Description
static class	ArcCosineUnitlengthDistance.Par	Parameterization class.

Field Summary

Fields

Modifier and Type	Field	Description
static ArcCosineUnitlengthDistance	STATIC	Static instance

Constructor Summary

Constructors

Constructor	Description
ArcCosineUnitlengthDistance()	Deprecated. Use static instance!

Method Summary

Modifier and Type	Method	Description
double	distance(NumberVector v1, NumberVector v2)	Computes the distance between two given DatabaseObjects according to this distance function.
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 elki.distance.Distance

isMetric, isSquared, isSymmetric

Methods inherited from interface elki.distance.SpatialPrimitiveDistance

instantiate

Field Detail

STATIC

public static final ArcCosineUnitlengthDistance STATIC

Static instance

Constructor Detail

ArcCosineUnitlengthDistance

@Deprecated
public ArcCosineUnitlengthDistance()

Deprecated.

Use static instance!

Constructor - use STATIC instead.

Method Detail

distance

public double distance(NumberVector v1,
                       NumberVector v2)

Description copied from interface: PrimitiveDistance

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

Specified by:

distance in interface NumberVectorDistance<NumberVector>

Specified by:

distance in interface PrimitiveDistance<NumberVector>

Parameters:

v1 - first DatabaseObject

v2 - second DatabaseObject

Returns:

the distance between two given DatabaseObjects according to this distance function

minDist

public double minDist(SpatialComparable mbr1,
                      SpatialComparable mbr2)

Description copied from interface: SpatialPrimitiveDistance

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

Specified by:

minDist in interface SpatialPrimitiveDistance<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: Distance

Get the input data type of the function.

Specified by:

getInputTypeRestriction in interface Distance<NumberVector>

Specified by:

getInputTypeRestriction in interface PrimitiveDistance<NumberVector>

Returns:

Type restriction