com.yelp.nrtsearch.server.luceneserver.search.query.multifunction.GuassianDecayFunction Maven / Gradle / Ivy

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GRPC lucene server using near-real-time replication

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/*
 * Copyright 2024 Yelp Inc.
 *
 * Licensed 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 com.yelp.nrtsearch.server.luceneserver.search.query.multifunction;

import org.apache.lucene.search.Explanation;

public class GuassianDecayFunction implements DecayFunction {
  @Override
  public double computeScore(double distance, double offset, double scale) {
    return Math.exp((-1.0 * Math.pow(Math.max(0.0, distance - offset), 2.0)) / (2.0 * scale));
  }

  @Override
  public double computeScale(double scale, double decay) {
    return (-1.0 * Math.pow(scale, 2.0)) / (2.0 * Math.log(decay));
  }

  @Override
  public Explanation explainComputeScore(double distance, double offset, double scale) {
    return Explanation.match(
        (float) computeScore(distance, offset, scale),
        "exp(- pow(max(0.0, |" + distance + " - " + offset + "), 2.0)/ (2.0 * " + scale + ")");
  }
}