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

    All Methods Instance Methods Concrete Methods
    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`

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