## org.apache.lucene.search.similarities
Class BasicModelD

    java.lang.Object
      org.apache.lucene.search.similarities.BasicModel
          org.apache.lucene.search.similarities.BasicModelD

    public class BasicModelD

extends BasicModel

Implements the approximation of the binomial model with the divergence for DFR. The formula used in Lucene differs slightly from the one in the original paper: to avoid underflow for small values of `N` and `F`, `N` is increased by `1` and `F` is always increased by `tfn+1`.

WARNING: for terms that do not meet the expected random distribution (e.g. stopwords), this model may give poor performance, such as abnormally high scores for low tf values.

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

Constructor Summary
`BasicModelD()` Sole constructor: parameter-free

Method Summary
`float` `score(BasicStats stats, float tfn)` Returns the informative content score.
`String` `toString()` Subclasses must override this method to return the code of the basic model formula.

Methods inherited from class org.apache.lucene.search.similarities.BasicModel
`explain`

Methods inherited from class java.lang.Object
`clone, equals, finalize, getClass, hashCode, notify, notifyAll, wait, wait, wait`

Constructor Detail

### BasicModelD

    public BasicModelD()

  Sole constructor: parameter-free

Method Detail

### score

    public final float score(BasicStats stats,
                             float tfn)

  Description copied from class: `BasicModel`
  Returns the informative content score.

  Specified by:
    `score` in class `BasicModel`

### toString

    public String toString()

  Description copied from class: `BasicModel`
  Subclasses must override this method to return the code of the basic model formula. Refer to the original paper for the list.

  Specified by:
    `toString` in class `BasicModel`

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