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

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 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

getClass, notify, notifyAll, wait, wait, wait

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 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