org.apache.lucene.search.similarities

Class IndriDirichletSimilarity

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.IndriDirichletSimilarity

public class IndriDirichletSimilarity
extends LMSimilarity

Bayesian smoothing using Dirichlet priors as implemented in the Indri Search engine (http://www.lemurproject.org/indri.php). Indri Dirichelet Smoothing!

 tf_E + mu*P(t|D) P(t|E)= documentLength + documentMu
 mu*P(t|C) + tf_D where P(t|D)= doclen + mu
 

A larger value for mu, produces more smoothing. Smoothing is most important for short documents where the probabilities are more granular.

Nested Class Summary

Nested Classes

Modifier and Type	Class and Description
static class	IndriDirichletSimilarity.IndriCollectionModel Models p(w|C) as the number of occurrences of the term in the collection, divided by the total number of tokens + 1.

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

Field Summary

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

collectionModel

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

discountOverlaps

Constructor Summary

Constructors

Constructor and Description
IndriDirichletSimilarity() Instantiates the similarity with the default μ value of 2000.
IndriDirichletSimilarity(float mu) Instantiates the similarity with the provided μ parameter.
IndriDirichletSimilarity(LMSimilarity.CollectionModel collectionModel) Instantiates the similarity with the default μ value of 2000.
IndriDirichletSimilarity(LMSimilarity.CollectionModel collectionModel, float mu) Instantiates the similarity with the provided μ parameter.

Method Summary

Modifier and Type	Method and Description
protected void	explain(List<Explanation> subs, BasicStats stats, double freq, double docLen) Subclasses should implement this method to explain the score.
float	getMu() Returns the μ parameter.
String	getName() Returns the name of the LM method.
protected double	score(BasicStats stats, double freq, double docLen) Scores the document doc.

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

fillBasicStats, newStats, toString

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

computeNorm, explain, getDiscountOverlaps, log2, scorer, setDiscountOverlaps

Methods inherited from class java.lang.Object

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

Constructor Detail

IndriDirichletSimilarity

public IndriDirichletSimilarity(LMSimilarity.CollectionModel collectionModel,
                                float mu)

Instantiates the similarity with the provided μ parameter.

IndriDirichletSimilarity

public IndriDirichletSimilarity(float mu)

Instantiates the similarity with the provided μ parameter.

IndriDirichletSimilarity

public IndriDirichletSimilarity(LMSimilarity.CollectionModel collectionModel)

Instantiates the similarity with the default μ value of 2000.

IndriDirichletSimilarity

public IndriDirichletSimilarity()

Instantiates the similarity with the default μ value of 2000.

Method Detail

score

protected double score(BasicStats stats,
                       double freq,
                       double docLen)

Description copied from class: SimilarityBase

Scores the document doc.

Subclasses must apply their scoring formula in this class.

Specified by:

score in class SimilarityBase

Parameters:

stats - the corpus level statistics.

freq - the term frequency.

docLen - the document length.

Returns:

the score.

explain

protected void explain(List<Explanation> subs,
                       BasicStats stats,
                       double freq,
                       double docLen)

Description copied from class: SimilarityBase

Subclasses should implement this method to explain the score. expl already contains the score, the name of the class and the doc id, as well as the term frequency and its explanation; subclasses can add additional clauses to explain details of their scoring formulae.

The default implementation does nothing.

Overrides:

explain in class LMSimilarity

Parameters:

subs - the list of details of the explanation to extend

stats - the corpus level statistics.

freq - the term frequency.

docLen - the document length.

getMu

public float getMu()

Returns the μ 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