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* http://www.apache.org/licenses/LICENSE-2.0
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package org.elasticsearch.index.query.functionscore;
import org.apache.lucene.search.Explanation;
/**
* Implement this interface to provide a decay function that is executed on a
* distance. For example, this could be an exponential drop of, a triangle
* function or something of the kind. This is used, for example, by
* {@link GaussDecayFunctionBuilder}.
*
*/
public interface DecayFunction {
double evaluate(double value, double scale);
Explanation explainFunction(String valueString, double value, double scale);
/**
* The final scale parameter is computed from the scale parameter given by
* the user and a value. This value is the value that the decay function
* should compute if document distance and user defined scale equal. The
* scale parameter for the function must be adjusted accordingly in this
* function
*
* @param scale
* the raw scale value given by the user
* @param decay
* the value which decay function should take once the distance
* reaches this scale
* */
double processScale(double scale, double decay);
}