Package 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
  Description
  `protected final float`
  `a`
  `protected final float`
  `b`
  `protected final float`
  `m`
  `protected final ValueSource`
  `source`

- ## Constructor Summary

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

- ## Method Summary

  Modifier and Type
  Method
  Description
  `void`
  `createWeight(Map<Object,Object> 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<Object,Object> context, LeafReaderContext 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

  `asDoubleValuesSource, asLongValuesSource, fromDoubleValuesSource, getSortField, newContext, toString`

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

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

- ## Field Details

  - ### source

    protected final ValueSource source

  - ### m

    protected final float m

  - ### a

    protected final float a

  - ### b

    protected final float b

- ## Constructor Details

  - ### ReciprocalFloatFunction

    public ReciprocalFloatFunction(ValueSource source, float m, float a, float b)
    f(source) = a/(m*float(source)+b)

- ## Method Details

  - ### getValues

    public FunctionValues getValues(Map<Object,Object> context, LeafReaderContext readerContext) throws IOException
    Description copied from class: `ValueSource`
    Gets the values for this reader and the context that was previously passed to createWeight(). The values must be consumed in a forward docID manner, and you must call this method again to iterate through the values again.
    Specified by:
      `getValues` in class `ValueSource`
    Throws:
      `IOException`

  - ### createWeight

    public void createWeight(Map<Object,Object> 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`