/*
Copyright (C) 2001 Kyle Siegrist, Dawn Duehring
This program 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 distributions;
/**The binomial distribution with a random number of trials*/
public class BinomialRandomNDistribution extends Distribution{
//Variables
double probability, sum;
Distribution dist;
/**This general constructor creates a new randomized binomial distribution with a specified probability of success and a specified distribution for
the number of trials*/
public BinomialRandomNDistribution(Distribution d, double p){
setParameters(d, p);
}
/**Special constructor: creates a new randomized binomial distribution with a specified probability of success and the uniform distribution on {1, 2, 3, 4, 5, 6} for the number of trials*/
public BinomialRandomNDistribution(double p){
this(new DiscreteUniformDistribution(1, 6, 1), p);
}
/**This default constructor: creates a new randomized binomial distribution with probability of success 0.5 and the uniform distribution on {1, 2, 3, 4, 5, 6} for the number of trials*/
public BinomialRandomNDistribution(){
this(new DiscreteUniformDistribution(1, 6, 1), 0.5);
}
/**Set the parameters: the distribution for the number of trials and the
probability of success*/
public void setParameters(Distribution d, double p){
dist = d;
probability = p;
super.setParameters(0, dist.getDomain().getUpperValue(), 1, DISCRETE);
}
//Density
public double getDensity(double x){
int k = (int)Math.rint(x);
double trials;
if (probability == 0){
if (k == 0) return 1;
else return 0;
}
else if (probability == 1) return dist.getDensity(k);
else{
sum = 0;
for(int i = 0; i < dist.getDomain().getSize(); i++){
trials = dist.getDomain().getValue(i);
sum = sum + dist.getDensity(trials) *
comb(trials, k) * Math.pow(probability, k) * Math.pow(1 - probability, trials - k);
}
return sum;
}
}
public double getMean(){
return dist.getMean() * probability;
}
public double getVariance(){
return dist.getMean() * probability * (1 - probability) + dist.getVariance() * probability * probability;
}
public double simulate(){
int trials = (int)dist.simulate();
int successes = 0;
for (int i = 1; i <= trials; i++){
if (Math.random() < probability) successes++;
}
return successes;
}
}