/*
* Title: CloudSim Toolkit
* Descripimport java.util.Random;
mulation) Toolkit for Modeling and Simulation of Clouds
* Licence: GPL - http://www.gnu.org/copyleft/gpl.html
*
* Copyright (c) 2009-2012, The University of Melbourne, Australia
*/
package org.cloudbus.cloudsim.distributions;
import java.util.Random;
/**
* The Class GammaDistr.
*
* @author Marcos Dias de Assuncao
* @since CloudSim Toolkit 1.0
*/
public class GammaDistr implements ContinuousDistribution {
/** The num gen. */
private final Random numGen;
/** The alpha. */
private final int alpha;
/** The beta. */
private final double beta;
/**
* Instantiates a new gamma distr.
*
* @param seed the seed
* @param alpha the alpha
* @param beta the beta
*/
public GammaDistr(Random seed, int alpha, double beta) {
if (alpha <= 0 || beta <= 0.0) {
throw new IllegalArgumentException("Alpha and beta must be greater than 0.0");
}
numGen = seed;
this.alpha = alpha;
this.beta = beta;
}
/**
* Instantiates a new gamma distr.
*
* @param alpha the alpha
* @param beta the beta
*/
public GammaDistr(int alpha, double beta) {
if (alpha <= 0 || beta <= 0.0) {
throw new IllegalArgumentException("Alpha and beta must be greater than 0.0");
}
numGen = new Random(System.currentTimeMillis());
this.alpha = alpha;
this.beta = beta;
}
/*
* (non-Javadoc)
* @see cloudsim.distributions.ContinuousDistribution#sample()
*/
@Override
public double sample() {
double sum = 0.0;
for (int i = 0; i < alpha; i++) {
sum += Math.log(numGen.nextDouble());
}
return -beta * sum;
}
}