org.terrier.matching.models
Class LGD

java.lang.Object
  org.terrier.matching.models.WeightingModel
      org.terrier.matching.models.LGD

All Implemented Interfaces:

java.io.Serializable, java.lang.Cloneable, Model

public class LGD
extends WeightingModel

This class implements the LGD weighting model. For more information about this model, see:

1. Stephane Clinchant and Eric Gaussier. Bridging Language Modeling and Divergence From Randomness Approaches: A Log-logistic Model for IR. ICTIR 2009, London, UK.
2. Stephane Clinchant and Eric Gaussier. Information-Based Models for Ad Hoc Information Retrieval. SIGIR 2010, Geneva, Switzerland.

Author:

Gianni Amati

See Also:

Serialized Form

Field Summary

Fields inherited from class org.terrier.matching.models.WeightingModel

averageDocumentLength, c, documentFrequency, i, keyFrequency, numberOfDocuments, numberOfPointers, numberOfTokens, numberOfUniqueTerms, termFrequency

Constructor Summary

LGD()
A default constructor.

LGD(double c)
Constructs an instance of this class with the specified value for the parameter c.

Method Summary

java.lang.String	getInfo() Returns the name of the model.
double	score(double tf, double docLength) Uses LGD to compute a weight for a term in a document.
double	score(double tf, double docLength, double n_t, double F_t, double keyFrequency) Uses LGD to compute a weight for a term in a document.

Methods inherited from class org.terrier.matching.models.WeightingModel

clone, getOverflowed, getParameter, prepare, score, setAverageDocumentLength, setCollectionStatistics, setDocumentFrequency, setEntryStatistics, setKeyFrequency, setNumberOfDocuments, setNumberOfPointers, setNumberOfTokens, setNumberOfUniqueTerms, setParameter, setRequest, setTermFrequency, stirlingPower

Methods inherited from class java.lang.Object

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

Constructor Detail

LGD

public LGD()

A default constructor. This must be followed by specifying the c value.

LGD

public LGD(double c)

Constructs an instance of this class with the specified value for the parameter c.

Parameters:

c - the term frequency normalisation parameter value.

Method Detail

getInfo

public final java.lang.String getInfo()

Returns the name of the model.

Specified by:

getInfo in interface Model

Specified by:

getInfo in class WeightingModel

Returns:

the name of the model

score

public final double score(double tf,
                          double docLength)

Uses LGD to compute a weight for a term in a document.

Specified by:

score in class WeightingModel

Parameters:

tf - The term frequency in the document

docLength - the document's length

Returns:

the score assigned to a document with the given tf and docLength, and other preset parameters

score

public final double score(double tf,
                          double docLength,
                          double n_t,
                          double F_t,
                          double keyFrequency)

Uses LGD to compute a weight for a term in a document.

Specified by:

score in class WeightingModel

Parameters:

tf - The term frequency in the document

docLength - the document's length

n_t - The document frequency of the term

F_t - the term frequency in the collection

keyFrequency - the term frequency in the query

Returns:

the score assigned by the weighting model LGD.