Class LMSimilarity

Abstract superclass for language modeling Similarities. The following inner types are introduced:

  • LMSimilarity.LMStats, which defines a new statistic, the probability that the collection language model generates the current term;
  • LMSimilarity.ICollectionModel, which is a strategy interface for object that compute the collection language model p(w|C);
  • LMSimilarity.DefaultCollectionModel, an implementation of the former, that computes the term probability as the number of occurrences of the term in the collection, divided by the total number of tokens.

Note

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

Inheritance
object
Similarity
SimilarityBase
LMSimilarity
LMDirichletSimilarity
LMJelinekMercerSimilarity
Inherited Members
Namespace: Lucene.Net.Search.Similarities
Assembly: Lucene.Net.dll
Syntax
public abstract class LMSimilarity : SimilarityBase

Constructors

LMSimilarity()

Creates a new instance with the default collection language model.

Declaration
protected LMSimilarity()

LMSimilarity(ICollectionModel)

Creates a new instance with the specified collection language model.

Declaration
protected LMSimilarity(LMSimilarity.ICollectionModel collectionModel)
Parameters
Type Name Description
LMSimilarity.ICollectionModel collectionModel

Fields

m_collectionModel

The collection model.

Declaration
protected readonly LMSimilarity.ICollectionModel m_collectionModel
Field Value
Type Description
LMSimilarity.ICollectionModel

Methods

Explain(Explanation, BasicStats, int, float, float)

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.

Declaration
protected override void Explain(Explanation expl, BasicStats stats, int doc, float freq, float docLen)
Parameters
Type Name Description
Explanation expl

the explanation to extend with details.
BasicStats stats

the corpus level statistics.
int doc

the document id.
float freq

the term frequency.
float docLen

the document length.
Overrides

FillBasicStats(BasicStats, CollectionStatistics, TermStatistics)

Computes the collection probability of the current term in addition to the usual statistics.

Declaration
protected override void FillBasicStats(BasicStats stats, CollectionStatistics collectionStats, TermStatistics termStats)
Parameters
Type Name Description
BasicStats stats
CollectionStatistics collectionStats
TermStatistics termStats
Overrides

GetName()

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

Used in ToString()

.
Declaration
public abstract string GetName()
Returns
Type Description
string

NewStats(string, float)

Factory method to return a custom stats object

Declaration
protected override BasicStats NewStats(string field, float queryBoost)
Parameters
Type Name Description
string field
float queryBoost
Returns
Type Description
BasicStats
Overrides

ToString()

Returns the name of the LM method. If a custom collection model strategy is used, its name is included as well.

Declaration
public override string ToString()
Returns
Type Description
string
Overrides
See Also