LGD (Terrier Information Retrieval Platform 5.5 API)

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, cs, documentFrequency, es, i, keyFrequency, numberOfDocuments, numberOfPointers, numberOfPostings, numberOfTokens, numberOfUniqueTerms, rq, termFrequency

Constructor Summary

Constructors
Constructor Description

LGD()
A default constructor.

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

Method Summary

All Methods Instance Methods Concrete Methods
Modifier and Type	Method	Description
`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.

Methods inherited from class org.terrier.matching.models.WeightingModel
clone, getOverflowed, getParameter, prepare, score, setCollectionStatistics, setEntryStatistics, setKeyFrequency, setParameter, setRequest

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