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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
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 |
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Nested classes/interfaces inherited from class org.apache.lucene.search.similarities.LMSimilarity |
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LMSimilarity.CollectionModel, LMSimilarity.DefaultCollectionModel, LMSimilarity.LMStats |
Nested classes/interfaces inherited from class org.apache.lucene.search.similarities.Similarity |
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Similarity.ExactSimScorer, Similarity.SimWeight, Similarity.SloppySimScorer |
Field Summary |
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Fields inherited from class org.apache.lucene.search.similarities.LMSimilarity |
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collectionModel |
Fields inherited from class org.apache.lucene.search.similarities.SimilarityBase |
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discountOverlaps |
Constructor Summary | |
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LMJelinekMercerSimilarity(float lambda)
Instantiates with the specified λ parameter. |
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LMJelinekMercerSimilarity(LMSimilarity.CollectionModel collectionModel,
float lambda)
Instantiates with the specified collectionModel and λ parameter. |
Method Summary | |
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protected void |
explain(Explanation expl,
BasicStats stats,
int doc,
float freq,
float docLen)
Subclasses should implement this method to explain the score. |
float |
getLambda()
Returns the λ parameter. |
String |
getName()
Returns the name of the LM method. |
protected float |
score(BasicStats stats,
float freq,
float docLen)
Scores the document doc . |
Methods inherited from class org.apache.lucene.search.similarities.LMSimilarity |
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fillBasicStats, newStats, toString |
Methods inherited from class org.apache.lucene.search.similarities.SimilarityBase |
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computeNorm, computeWeight, decodeNormValue, encodeNormValue, exactSimScorer, explain, getDiscountOverlaps, log2, setDiscountOverlaps, sloppySimScorer |
Methods inherited from class org.apache.lucene.search.similarities.Similarity |
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coord, queryNorm |
Methods inherited from class java.lang.Object |
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clone, equals, finalize, getClass, hashCode, notify, notifyAll, wait, wait, wait |
Constructor Detail |
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public LMJelinekMercerSimilarity(LMSimilarity.CollectionModel collectionModel, float lambda)
public LMJelinekMercerSimilarity(float lambda)
Method Detail |
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protected float score(BasicStats stats, float freq, float docLen)
SimilarityBase
doc
.
Subclasses must apply their scoring formula in this class.
score
in class SimilarityBase
stats
- the corpus level statistics.freq
- the term frequency.docLen
- the document length.
protected void explain(Explanation expl, BasicStats stats, int doc, float freq, float docLen)
SimilarityBase
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.
explain
in class LMSimilarity
expl
- the explanation to extend with details.stats
- the corpus level statistics.doc
- the document id.freq
- the term frequency.docLen
- the document length.public float getLambda()
public String getName()
LMSimilarity
Used in LMSimilarity.toString()
getName
in class LMSimilarity
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