PoissonDistribution.java

/**
 * This file is part of the Kompics P2P Framework.
 *
 * Copyright (C) 2009 Swedish Institute of Computer Science (SICS)
 * Copyright (C) 2009 Royal Institute of Technology (KTH)
 *
 * Kompics is free software; you can redistribute it and/or
 * modify it under the terms of the GNU General Public License
 * as published by the Free Software Foundation; either version 2
 * of the License, or (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program; if not, write to the Free Software
 * Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA  02111-1307, USA.
 */package se.sics.gvod.simulator.vod;

import java.util.Random;
import se.sics.kompics.p2p.experiment.dsl.distribution.Distribution;

public final class PoissonDistribution extends Distribution<Long> {

    /**
     *
     */
    private static final long serialVersionUID = 6665221714177817925L;
    private double lambda;
    private Random rand;

    public PoissonDistribution(Long lambda, Random random) {
        super(Type.OTHER, Long.class);
        this.lambda=lambda;
        this.rand = random;
    }

    @Override
    public Long draw() {
        double product = 1;
        long count = 0;
        long result = 0;
        while(Math.log(product)>=-lambda){
//        while (product >= elambda) {
            product *= rand.nextDouble();
            result = count;
            count++; // keep result one behind
        }
        return result;
    }
}