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

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Here is the source code for com.facebook.LinkBench.distributions.LogNormalDistribution.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.utils.ConfigUtil;

public class LogNormalDistribution implements ProbabilityDistribution {
    private long min;
    private long max;
    private double mu; // mean of the natural log of random variable
    private double sigma; // standard deviation of natural log of random variable

    public static final String CONFIG_MEDIAN = "median";
    public static final String CONFIG_SIGMA = "sigma";

    @Override
    public void init(long min, long max, Properties props, String keyPrefix) {
        double sigma = ConfigUtil.getDouble(props, CONFIG_SIGMA);
        double median = ConfigUtil.getDouble(props, CONFIG_MEDIAN);
        init(min, max, median, sigma);
    }

    /**
     *
     * @param min
     * @param max
     * @param median the median value of the distribution
     * @param sigma the standard deviation of the natural log of the variable
     * @param scale
     */
    public void init(long min, long max, double median, double sigma) {
        this.min = min;
        this.max = max;
        this.mu = FastMath.log(median);
        this.sigma = sigma;
    }

    @Override
    public double pdf(long id) {
        throw new RuntimeException("pdf not implemented");
    }

    @Override
    public double expectedCount(long id) {
        throw new RuntimeException("expectedCount not implemented");
    }

    @Override
    public double cdf(long id) {
        if (id < min)
            return 0.0;
        if (id >= max)
            return 1.0;
        org.apache.commons.math3.distribution.LogNormalDistribution d = new org.apache.commons.math3.distribution.LogNormalDistribution(
                mu, sigma);
        return d.cumulativeProbability(id);
    }

    @Override
    public long choose(Random rng) {
        long choice = (long) Math.round(FastMath.exp((rng.nextGaussian() * sigma) + mu));
        if (choice < min)
            return min;
        else if (choice >= max)
            return max - 1;
        else
            return choice;
    }

    @Override
    public long quantile(double p) {
        throw new RuntimeException("Quantile not implemented");
    }

}