exponentialdistribution.java

发布/订阅系统路由重配算法,可应用于ad hoc环境

package sim;

import java.util.*;

/**
 * This class provides exponential distributed values.
 */
public class ExponentialDistribution implements Distribution {

	private Random rand;
	private double lambda;

	public ExponentialDistribution(Random rand, double lambda) {
		this.rand = rand;
		this.lambda = lambda;
	}
	
	public double getValue() {
		/*
		 * r = 1 - e^{-\lamda t} => t = - ln(1-r) / \lambda
		 */
		return -Math.log(1 - rand.nextDouble()) / lambda;
	}

	public double getExpectedValue() {
		return 1.0 / lambda;
	}

    public double getVariance() {
		return 1.0 / (lambda*lambda);
    }
}