DistBinomial.java
package nl.tudelft.simulation.jstats.distributions;
import org.djutils.exceptions.Throw;
import nl.tudelft.simulation.jstats.math.ProbMath;
import nl.tudelft.simulation.jstats.streams.StreamInterface;
/**
* The Binomial distribution. The binomial distribution is the probability of the number of successes in a sequence of n
* independent experiments, each with success (probability p) or failure (probability q = 1 − p). For more information on this
* distribution see <a href="https://mathworld.wolfram.com/BinomialDistribution.html">
* https://mathworld.wolfram.com/BinomialDistribution.html </a>
* <p>
* Copyright (c) 2002-2024 Delft University of Technology, Jaffalaan 5, 2628 BX Delft, the Netherlands. All rights reserved. See
* for project information <a href="https://simulation.tudelft.nl/" target="_blank"> https://simulation.tudelft.nl</a>. The DSOL
* project is distributed under a three-clause BSD-style license, which can be found at
* <a href="https://https://simulation.tudelft.nl/dsol/docs/latest/license.html" target="_blank">
* https://https://simulation.tudelft.nl/dsol/docs/latest/license.html</a>.
* </p>
* @author <a href="https://www.linkedin.com/in/peterhmjacobs">Peter Jacobs </a>
* @author <a href="https://www.tudelft.nl/averbraeck">Alexander Verbraeck</a>
*/
public class DistBinomial extends DistDiscrete
{
/** */
private static final long serialVersionUID = 1L;
/** n is the number of independent experiments for the Binomial distribution. */
private final int n;
/** p is the probability of success for each individual trial in the binomial distribution. */
private final double p;
/**
* constructs a Binomial distribution. It calculates the probability for a number of successes in n independent Bernoulli
* trials with probability p of success on each trial.
* @param stream StreamInterface; the random number stream
* @param n long; the number of independent experiments for the Binomial distribution
* @param p double; the probability of success for each individual trial in the binomial distribution
* @throws IllegalArgumentException when n <= 0 or p <= 0 or p >= 1
*/
public DistBinomial(final StreamInterface stream, final int n, final double p)
{
super(stream);
Throw.when(n <= 0 || p <= 0 || p >= 1, IllegalArgumentException.class, "Error Binomial - n<=0 or p<=0.0 or p>=1.0");
this.n = n;
this.p = p;
}
/** {@inheritDoc} */
@Override
public long draw()
{
long x = 0;
for (int i = 0; i < this.n; i++)
{
if (this.stream.nextDouble() <= this.p)
{
x++;
}
}
return x;
}
/** {@inheritDoc} */
@Override
public double probability(final long observation)
{
if (observation <= this.n && observation >= 0)
{
return ProbMath.combinations(this.n, observation) * Math.pow(this.p, observation)
* Math.pow(1 - this.p, this.n - observation);
}
return 0.0;
}
/**
* Return the number of independent experiments for the Binomial distribution.
* @return int; the number of independent experiments for the Binomial distribution
*/
public int getN()
{
return this.n;
}
/**
* Return the probability of success for each individual trial in the binomial distribution.
* @return double; the probability of success for each individual trial in the binomial distribution
*/
public double getP()
{
return this.p;
}
/** {@inheritDoc} */
@Override
public String toString()
{
return "Binomial(" + this.n + "," + this.p + ")";
}
}