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