org.apache.lucene.queries.function.valuesource

## Class ReciprocalFloatFunction

- java.lang.Object
- - org.apache.lucene.queries.function.ValueSource
  - - org.apache.lucene.queries.function.valuesource.ReciprocalFloatFunction

-     public class ReciprocalFloatFunction
      extends ValueSource

  `ReciprocalFloatFunction` implements a reciprocal function f(x) = a/(mx+b), based on the float value of a field or function as exported by `ValueSource`.
  When a and b are equal, and x>=0, this function has a maximum value of 1 that drops as x increases. Increasing the value of a and b together results in a movement of the entire function to a flatter part of the curve.

  These properties make this an idea function for boosting more recent documents.

  Example:`recip(ms(NOW,mydatefield),3.16e-11,1,1)`

  A multiplier of 3.16e-11 changes the units from milliseconds to years (since there are about 3.16e10 milliseconds per year). Thus, a very recent date will yield a value close to 1/(0+1) or 1, a date a year in the past will get a multiplier of about 1/(1+1) or 1/2, and date two years old will yield 1/(2+1) or 1/3.

  See Also:
    `FunctionQuery`

- - ### Field Summary

    Fields
    Modifier and Type | Field and Description
    --- | ---
    `protected float` | `a`
    `protected float` | `b`
    `protected float` | `m`
    `protected ValueSource` | `source`

  - ### Constructor Summary

    Constructors
    Constructor and Description
    `ReciprocalFloatFunction(ValueSource source, float m, float a, float b)` f(source) = a/(m*float(source)+b)

  - ### Method Summary

    Methods
    Modifier and Type | Method and Description
    --- | ---
    `void` | `createWeight(Map context, IndexSearcher searcher)` Implementations should propagate createWeight to sub-ValueSources which can optionally store weight info in the context.
    `String` | `description()` description of field, used in explain()
    `boolean` | `equals(Object o)`
    `FunctionValues` | `getValues(Map context, AtomicReaderContext readerContext)` Gets the values for this reader and the context that was previously passed to createWeight()
    `int` | `hashCode()`

    - ### Methods inherited from class org.apache.lucene.queries.function.ValueSource

      `getSortField, newContext, toString`

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

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

- - ### Field Detail

    - #### source

          protected final ValueSource source

    - #### m

          protected final float m

    - #### a

          protected final float a

    - #### b

          protected final float b

  - ### Constructor Detail

    - #### ReciprocalFloatFunction

          public ReciprocalFloatFunction(ValueSource source,
                                 float m,
                                 float a,
                                 float b)

      f(source) = a/(m*float(source)+b)

  - ### Method Detail

    - #### getValues

          public FunctionValues getValues(Map context,
                                 AtomicReaderContext readerContext)
                                   throws IOException

      Description copied from class: `ValueSource`
      Gets the values for this reader and the context that was previously passed to createWeight()
      Specified by:
        `getValues` in class `ValueSource`
      Throws:
        `IOException`

    - #### createWeight

          public void createWeight(Map context,
                          IndexSearcher searcher)
                            throws IOException

      Description copied from class: `ValueSource`
      Implementations should propagate createWeight to sub-ValueSources which can optionally store weight info in the context. The context object will be passed to getValues() where this info can be retrieved.
      Overrides:
        `createWeight` in class `ValueSource`
      Throws:
        `IOException`

    - #### description

          public String description()

      Description copied from class: `ValueSource`
      description of field, used in explain()
      Specified by:
        `description` in class `ValueSource`

    - #### hashCode

          public int hashCode()

      Specified by:
        `hashCode` in class `ValueSource`

    - #### equals

          public boolean equals(Object o)

      Specified by:
        `equals` in class `ValueSource`

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