org.elasticsearch.index.query.functionscore.gauss.GaussDecayFunctionParser Maven / Gradle / Ivy
/*
* Licensed to Elasticsearch under one or more contributor
* license agreements. See the NOTICE file distributed with
* this work for additional information regarding copyright
* ownership. Elasticsearch licenses this file to you under
* the Apache License, Version 2.0 (the "License"); you may
* not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing,
* software distributed under the License is distributed on an
* "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
* KIND, either express or implied. See the License for the
* specific language governing permissions and limitations
* under the License.
*/
package org.elasticsearch.index.query.functionscore.gauss;
import org.apache.lucene.search.ComplexExplanation;
import org.apache.lucene.search.Explanation;
import org.elasticsearch.index.query.functionscore.DecayFunction;
import org.elasticsearch.index.query.functionscore.DecayFunctionParser;
public class GaussDecayFunctionParser extends DecayFunctionParser {
static final DecayFunction decayFunction = new GaussScoreFunction();
public static final String[] NAMES = { "gauss" };
@Override
public DecayFunction getDecayFunction() {
return decayFunction;
}
final static class GaussScoreFunction implements DecayFunction {
@Override
public double evaluate(double value, double scale) {
// note that we already computed scale^2 in processScale() so we do
// not need to square it here.
return (float) Math.exp(0.5 * Math.pow(value, 2.0) / scale);
}
@Override
public Explanation explainFunction(String valueExpl, double value, double scale) {
ComplexExplanation ce = new ComplexExplanation();
ce.setValue((float) evaluate(value, scale));
ce.setDescription("-exp(-0.5*pow(" + valueExpl + ",2.0)/" + -1 * scale + ")");
return ce;
}
@Override
public double processScale(double scale, double decay) {
return 0.5 * Math.pow(scale, 2.0) / Math.log(decay);
}
}
@Override
public String[] getNames() {
return NAMES;
}
}