BetaDistributionNearbyRandom.java

/*
 * Copyright 2014 Red Hat, Inc. and/or its affiliates.
 *
 * 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 org.optaplanner.core.impl.heuristic.selector.common.nearby;

import java.util.Random;

import org.apache.commons.math3.distribution.BetaDistribution;

public class BetaDistributionNearbyRandom implements NearbyRandom {

    protected final BetaDistribution betaDistribution;

    public BetaDistributionNearbyRandom(double betaDistributionAlpha, double betaDistributionBeta) {
        if (betaDistributionAlpha <= 0) {
            throw new IllegalArgumentException("The betaDistributionAlpha (" + betaDistributionAlpha
                    + ") must be greater than 0.");
        }
        if (betaDistributionBeta <= 0) {
            throw new IllegalArgumentException("The betaDistributionBeta (" + betaDistributionBeta
                    + ") must be greater than 0.");
        }
        betaDistribution = new BetaDistribution(betaDistributionAlpha, betaDistributionBeta);
    }

    @Override
    public int nextInt(Random random, int nearbySize) {
        double d = betaDistribution.inverseCumulativeProbability(random.nextDouble());
        int next = (int) (d * (double) nearbySize);
        // The method inverseCumulativeProbability() might return 1.0
        if (next >= nearbySize) {
            next = nearbySize - 1;
        }
        return next;
    }

    @Override
    public int getOverallSizeMaximum() {
        return Integer.MAX_VALUE;
    }

}