Package org.apache.lucene.search.similarities

Class LMDirichletSimilarity

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.LMDirichletSimilarity
public class LMDirichletSimilarity extends LMSimilarity
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.

  • Constructor Details

    • LMDirichletSimilarity

      public LMDirichletSimilarity(LMSimilarity.CollectionModel collectionModel, float mu)
      Instantiates the similarity with the provided μ parameter.

    • LMDirichletSimilarity

      public LMDirichletSimilarity(float mu)
      Instantiates the similarity with the provided μ parameter.

    • LMDirichletSimilarity

      public LMDirichletSimilarity(LMSimilarity.CollectionModel collectionModel)
      Instantiates the similarity with the default μ value of 2000.

    • LMDirichletSimilarity

      public LMDirichletSimilarity()
      Instantiates the similarity with the default μ value of 2000.

  • Method Details

    • 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