com.facebook.LinkBench.distributions.GeometricDistribution.java Source code

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Here is the source code for com.facebook.LinkBench.distributions.GeometricDistribution.java

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/*
 * Copyright 2012, Facebook, 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.facebook.LinkBench.distributions;

import java.util.Properties;
import java.util.Random;

import org.apache.commons.math3.util.FastMath;

import com.oltpbenchmark.benchmarks.linkbench.LinkBenchConstants;
import com.oltpbenchmark.benchmarks.linkbench.utils.ConfigUtil;

/**
 * Geometric distribution
 *
 * NOTE: this generates values in the range [min, max).  Since the
 * real geometric distribution generates values in range [min, inf),
 * we truncate anything >= max
 */
public class GeometricDistribution implements ProbabilityDistribution {

    /** The probability parameter that defines the distribution */
    private double p = 0.0;

    /** Valid range */
    private long min = 0, max = 0;

    private double scale = 0.0;

    public static final String PROB_PARAM_KEY = "prob";

    @Override
    public void init(long min, long max, Properties props, String keyPrefix) {
        double parsedP = ConfigUtil.getDouble(props, keyPrefix + PROB_PARAM_KEY);

        double scaleVal = 1.0;
        ;
        if (props.containsKey(LinkBenchConstants.PROB_MEAN)) {
            scaleVal = (max - min) * ConfigUtil.getDouble(props, keyPrefix + LinkBenchConstants.PROB_MEAN);
        }
        init(min, max, parsedP, scaleVal);
    }

    public void init(long min, long max, double p, double scale) {
        this.min = min;
        this.max = max;
        this.p = p;
        this.scale = scale;
    }

    @Override
    public double pdf(long id) {
        return scaledPdf(id, 1.0);
    }

    @Override
    public double expectedCount(long id) {
        return scaledPdf(id, scale);
    }

    private double scaledPdf(long id, double scaleFactor) {
        if (id < min || id >= max)
            return 0.0;
        long x = id - min;
        return FastMath.pow(1 - p, x) * scaleFactor * p;
    }

    @Override
    public double cdf(long id) {
        if (id < min)
            return 0.0;
        if (id >= max)
            return 1.0;
        return 1 - FastMath.pow(1 - p, id - min + 1);
    }

    @Override
    public long choose(Random rng) {
        return quantile(rng.nextDouble());
    }

    @Override
    public long quantile(double r) {
        /*
         * Quantile function for geometric distribution over
         * range [0, inf) where 0 < r < 1
         * quantile(r) = ceiling(ln(1 - r) / ln (1 - p))
         * Source: http://www.math.uah.edu/stat/bernoulli/Geometric.html
         */
        if (r == 0.0)
            return min; // 0.0 must be handled specially

        long x = min + (long) FastMath.ceil(FastMath.log(1 - r) / FastMath.log(1 - p));
        // truncate over max
        return Math.min(x, max - 1);
    }

}