Package org.apache.lucene.queries.function.valuesource

Class 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 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​(java.util.Map context,
                                AtomicReaderContext readerContext)
                         throws java.io.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:
        java.io.IOException

      • createWeight

        public void createWeight​(java.util.Map context,
                         IndexSearcher searcher)
                  throws java.io.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:
        java.io.IOException

      • description

        public java.lang.String description()
        Description copied from class: ValueSource
        description of field, used in explain()
        Specified by:
        description in class ValueSource

      • equals

        public boolean equals​(java.lang.Object o)
        Specified by:
        equals in class ValueSource