org.apache.lucene.search.similarities

## Class AxiomaticF2EXP

- java.lang.Object
- - org.apache.lucene.search.similarities.Similarity
  - - org.apache.lucene.search.similarities.SimilarityBase
    - - org.apache.lucene.search.similarities.Axiomatic
      - - org.apache.lucene.search.similarities.AxiomaticF2EXP

-     public class AxiomaticF2EXP
      extends Axiomatic

  F2EXP is defined as Sum(tfln(term_doc_freq, docLen)*IDF(term)) where IDF(t) = pow((N+1)/df(t), k) N=total num of docs, df=doc freq
  WARNING: This API is experimental and might change in incompatible ways in the next release.

- - ### Nested Class Summary

    - ### 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.Axiomatic

      `k, queryLen, s`

    - ### Fields inherited from class org.apache.lucene.search.similarities.SimilarityBase

      `discountOverlaps`

  - ### Constructor Summary

    Constructors
    Constructor and Description
    `AxiomaticF2EXP()` Default constructor
    `AxiomaticF2EXP(float s)` Constructor setting s only, letting k and queryLen to default
    `AxiomaticF2EXP(float s, float k)` Constructor setting s and k, letting queryLen to default

  - ### Method Summary

    All Methods Instance Methods Concrete Methods
    Modifier and Type | Method and Description
    --- | ---
    `protected double` | `gamma(BasicStats stats, double freq, double docLen)` compute the gamma component
    `protected double` | `idf(BasicStats stats, double freq, double docLen)` compute the inverted document frequency component
    `protected Explanation` | `idfExplain(BasicStats stats, double freq, double docLen)` Explain the score of the inverted document frequency component for a single document
    `protected double` | `ln(BasicStats stats, double freq, double docLen)` compute the document length component
    `protected Explanation` | `lnExplain(BasicStats stats, double freq, double docLen)` Explain the score of the document length component for a single document
    `protected double` | `tf(BasicStats stats, double freq, double docLen)` compute the term frequency component
    `protected Explanation` | `tfExplain(BasicStats stats, double freq, double docLen)` Explain the score of the term frequency component for a single document
    `protected double` | `tfln(BasicStats stats, double freq, double docLen)` compute the mixed term frequency and document length component
    `protected Explanation` | `tflnExplain(BasicStats stats, double freq, double docLen)` Explain the score of the mixed term frequency and document length component for a single document
    `String` | `toString()` Name of the axiomatic method.

    - ### Methods inherited from class org.apache.lucene.search.similarities.Axiomatic

      `explain, explain, score`

    - ### Methods inherited from class org.apache.lucene.search.similarities.SimilarityBase

      `computeNorm, fillBasicStats, getDiscountOverlaps, log2, newStats, scorer, setDiscountOverlaps`

    - ### Methods inherited from class java.lang.Object

      `clone, equals, finalize, getClass, hashCode, notify, notifyAll, wait, wait, wait`

- - ### Constructor Detail

    - #### AxiomaticF2EXP

          public AxiomaticF2EXP(float s,
                                float k)

      Constructor setting s and k, letting queryLen to default
      Parameters:
        `s` - hyperparam for the growth function
        `k` - hyperparam for the primitive weighting function

    - #### AxiomaticF2EXP

          public AxiomaticF2EXP(float s)

      Constructor setting s only, letting k and queryLen to default
      Parameters:
        `s` - hyperparam for the growth function

    - #### AxiomaticF2EXP

          public AxiomaticF2EXP()

      Default constructor

  - ### Method Detail

    - #### toString

          public String toString()

      Description copied from class: `Axiomatic`
      Name of the axiomatic method.
      Specified by:
        `toString` in class `Axiomatic`

    - #### tf

          protected double tf(BasicStats stats,
                              double freq,
                              double docLen)

      compute the term frequency component
      Specified by:
        `tf` in class `Axiomatic`

    - #### ln

          protected double ln(BasicStats stats,
                              double freq,
                              double docLen)

      compute the document length component
      Specified by:
        `ln` in class `Axiomatic`

    - #### tfln

          protected double tfln(BasicStats stats,
                                double freq,
                                double docLen)

      compute the mixed term frequency and document length component
      Specified by:
        `tfln` in class `Axiomatic`

    - #### idf

          protected double idf(BasicStats stats,
                               double freq,
                               double docLen)

      compute the inverted document frequency component
      Specified by:
        `idf` in class `Axiomatic`

    - #### gamma

          protected double gamma(BasicStats stats,
                                 double freq,
                                 double docLen)

      compute the gamma component
      Specified by:
        `gamma` in class `Axiomatic`

    - #### tfExplain

          protected Explanation tfExplain(BasicStats stats,
                                          double freq,
                                          double docLen)

      Description copied from class: `Axiomatic`
      Explain the score of the term frequency component for a single document
      Specified by:
        `tfExplain` in class `Axiomatic`
      Parameters:
        `stats` - the corpus level statistics
        `freq` - number of occurrences of term in the document
        `docLen` - the document length
      Returns:
        Explanation of how the tf component was computed

    - #### lnExplain

          protected Explanation lnExplain(BasicStats stats,
                                          double freq,
                                          double docLen)

      Description copied from class: `Axiomatic`
      Explain the score of the document length component for a single document
      Specified by:
        `lnExplain` in class `Axiomatic`
      Parameters:
        `stats` - the corpus level statistics
        `freq` - number of occurrences of term in the document
        `docLen` - the document length
      Returns:
        Explanation of how the ln component was computed

    - #### tflnExplain

          protected Explanation tflnExplain(BasicStats stats,
                                            double freq,
                                            double docLen)

      Description copied from class: `Axiomatic`
      Explain the score of the mixed term frequency and document length component for a single document
      Specified by:
        `tflnExplain` in class `Axiomatic`
      Parameters:
        `stats` - the corpus level statistics
        `freq` - number of occurrences of term in the document
        `docLen` - the document length
      Returns:
        Explanation of how the tfln component was computed

    - #### idfExplain

          protected Explanation idfExplain(BasicStats stats,
                                           double freq,
                                           double docLen)

      Description copied from class: `Axiomatic`
      Explain the score of the inverted document frequency component for a single document
      Specified by:
        `idfExplain` in class `Axiomatic`
      Parameters:
        `stats` - the corpus level statistics
        `freq` - number of occurrences of term in the document
        `docLen` - the document length
      Returns:
        Explanation of how the idf component was computed

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