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

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, 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 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,
                                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 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