Class LMDirichletSimilarity

Bayesian smoothing using Dirichlet priors. 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 formula as defined the paper assigns a negative score to documents that contain the term, but with fewer occurrences than predicted by the collection language model. The Lucene implementation returns 0 for such documents.

Note

This API is experimental and might change in incompatible ways in the next release.

Inheritance
System.Object
Similarity
SimilarityBase
LMSimilarity
LMDirichletSimilarity
Inherited Members
System.Object.Equals(System.Object)
System.Object.Equals(System.Object, System.Object)
System.Object.GetHashCode()
System.Object.GetType()
System.Object.MemberwiseClone()
System.Object.ReferenceEquals(System.Object, System.Object)
Namespace: Lucene.Net.Search.Similarities
Assembly: Lucene.Net.dll
Syntax
public class LMDirichletSimilarity : LMSimilarity

Constructors

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LMDirichletSimilarity()

Instantiates the similarity with the default μ value of 2000.

Declaration
public LMDirichletSimilarity()
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LMDirichletSimilarity(LMSimilarity.ICollectionModel)

Instantiates the similarity with the default μ value of 2000.

Declaration
public LMDirichletSimilarity(LMSimilarity.ICollectionModel collectionModel)
Parameters
Type Name Description
LMSimilarity.ICollectionModel collectionModel
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LMDirichletSimilarity(LMSimilarity.ICollectionModel, Single)

Instantiates the similarity with the provided μ parameter.

Declaration
public LMDirichletSimilarity(LMSimilarity.ICollectionModel collectionModel, float mu)
Parameters
Type Name Description
LMSimilarity.ICollectionModel collectionModel
System.Single mu
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LMDirichletSimilarity(Single)

Instantiates the similarity with the provided μ parameter.

Declaration
public LMDirichletSimilarity(float mu)
Parameters
Type Name Description
System.Single mu

Properties

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Mu

Returns the μ parameter.

Declaration
public virtual float Mu { get; }
Property Value
Type Description
System.Single

Methods

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Explain(Explanation, BasicStats, Int32, Single, Single)

Declaration
protected override void Explain(Explanation expl, BasicStats stats, int doc, float freq, float docLen)
Parameters
Type Name Description
Explanation expl
BasicStats stats
System.Int32 doc
System.Single freq
System.Single docLen
Overrides
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GetName()

Declaration
public override string GetName()
Returns
Type Description
System.String
Overrides
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Score(BasicStats, Single, Single)

Declaration
public override float Score(BasicStats stats, float freq, float docLen)
Parameters
Type Name Description
BasicStats stats
System.Single freq
System.Single docLen
Returns
Type Description
System.Single
Overrides