org.apache.lucene.search.similarities

Class LMJelinekMercerSimilarity

java.lang.Object

org.apache.lucene.search.similarities.Similarity

org.apache.lucene.search.similarities.SimilarityBase

org.apache.lucene.search.similarities.LMSimilarity

org.apache.lucene.search.similarities.LMJelinekMercerSimilarity

public class LMJelinekMercerSimilarity
extends LMSimilarity

Language model based on the Jelinek-Mercer smoothing method. From Chengxiang Zhai and John Lafferty. 2001. A study of smoothing methods for language models applied to Ad Hoc information retrieval. In Proceedings of the 24th annual international ACM SIGIR conference on Research and development in information retrieval (SIGIR '01). ACM, New York, NY, USA, 334-342.

The model has a single parameter, λ. According to said paper, the optimal value depends on both the collection and the query. The optimal value is around 0.1 for title queries and 0.7 for long queries.

Nested Class Summary

Nested classes/interfaces inherited from class org.apache.lucene.search.similarities.LMSimilarity

LMSimilarity.CollectionModel, LMSimilarity.DefaultCollectionModel, LMSimilarity.LMStats

Nested classes/interfaces inherited from class org.apache.lucene.search.similarities.Similarity

Similarity.SimScorer, Similarity.SimWeight

Constructor Summary

Constructors

Constructor and Description
LMJelinekMercerSimilarity(float lambda) Instantiates with the specified λ parameter.
LMJelinekMercerSimilarity(LMSimilarity.CollectionModel collectionModel, float lambda) Instantiates with the specified collectionModel and λ parameter.

Method Summary

Modifier and Type	Method and Description
float	getLambda() Returns the λ parameter.
String	getName() Returns the name of the LM method.

Methods inherited from class org.apache.lucene.search.similarities.LMSimilarity

toString

Methods inherited from class org.apache.lucene.search.similarities.SimilarityBase

computeNorm, computeWeight, getDiscountOverlaps, log2, setDiscountOverlaps, simScorer

Methods inherited from class org.apache.lucene.search.similarities.Similarity

coord, queryNorm

Methods inherited from class java.lang.Object

equals, getClass, hashCode, notify, notifyAll, wait, wait, wait

Constructor Detail

LMJelinekMercerSimilarity

public LMJelinekMercerSimilarity(LMSimilarity.CollectionModel collectionModel,
                                 float lambda)

Instantiates with the specified collectionModel and λ parameter.

LMJelinekMercerSimilarity

public LMJelinekMercerSimilarity(float lambda)

Instantiates with the specified λ parameter.

Method Detail

getLambda

public float getLambda()

Returns the λ parameter.

getName

public String getName()

Description copied from class: LMSimilarity

Returns the name of the LM method. The values of the parameters should be included as well.

Used in LMSimilarity.toString()

.

Specified by:

getName in class LMSimilarity