jsc.distributions
Class Binomial

java.lang.Object
  |
  +--jsc.distributions.AbstractDistribution
        |
        +--jsc.distributions.AbstractDiscreteDistribution
              |
              +--jsc.distributions.Binomial

All Implemented Interfaces:

Distribution

public class Binomial

extends AbstractDiscreteDistribution

This class represents a binomial distribution.

Version:

1.0

Author:

A. J. Bertie.

Field Summary

Fields inherited from class jsc.distributions.AbstractDiscreteDistribution

maxValue, minValue

Fields inherited from class jsc.distributions.AbstractDistribution

rand

Constructor Summary

Binomial(long n, double p)
Create a binomial distribution with parameters n and p.

Method Summary

double	cdf(double x) Returns the value of the cumulative density function at a variate-value x.
long	getN()
double	getP()
double	inverseCdf(double prob) Returns the inverse of binomial distribution.
double	mean() Returns true indicating that the distribution is discrete.
double	pdf(double x) Returns the value of the probability mass function at variate-value x.
double	random() Returns as a double number an integer value that is a random variate-value drawn from the binomial distribution.
void	setN(long n) Change the "number of trials" parameter.
void	setP(double p) Change the "probability of success" parameter.
String	toString()
double	variance() Return variance of the distribution.

Methods inherited from class jsc.distributions.AbstractDiscreteDistribution

getMaximumPdf, getMaxValue, getMinValue, isDiscrete, moment, moment

Methods inherited from class jsc.distributions.AbstractDistribution

sd, setSeed

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, wait, wait, wait

Constructor Detail

Binomial

public Binomial(long n,
                double p)

Create a binomial distribution with parameters n and p.

Parameters:

n - the "number of trials" parameter; must be greater than 0.

p - the "probability of success" parameter; must be greater than 0 and less than 1.

Throws:

IllegalArgumentException - if n less than 1.

IllegalArgumentException - if p not in (0,1).

Method Detail

cdf

public double cdf(double x)

Returns the value of the cumulative density function at a variate-value x.

Specified by:

cdf in interface Distribution

Overrides:

cdf in class AbstractDiscreteDistribution

Parameters:

x - a variate-value; must be in [0,n].

Returns:

the value of the cumulative density function at x.

Throws:

IllegalArgumentException - if x less than 0 or greater than n.

getN

public long getN()

Returns:

the "number of trials" parameter.

getP

public double getP()

Returns:

the "probability of success" parameter.

inverseCdf

public double inverseCdf(double prob)

Returns the inverse of binomial distribution. Given a probability, returns the smallest integer value of x such that Prob(X <= x) >= prob is true.

Specified by:

inverseCdf in interface Distribution

Overrides:

inverseCdf in class AbstractDiscreteDistribution

Parameters:

prob - the value of the probability; must be in [0,1].

Returns:

the variate-value x.

Throws:

IllegalArgumentException - if prob is less than 0 or greater than 1.

mean

public double mean()

Returns true indicating that the distribution is discrete.

Specified by:

mean in interface Distribution

Overrides:

mean in class AbstractDiscreteDistribution

Returns:

true.

pdf

public double pdf(double x)

Returns the value of the probability mass function at variate-value x. Returns zero if x is not a valid variate-value.

Specified by:

pdf in interface Distribution

Specified by:

pdf in class AbstractDiscreteDistribution

Parameters:

x - a variate-value.

Returns:

the value of the pmf at x if x is in [0,n]; otherwise returns 0.

random

public double random()

Returns as a double number an integer value that is a random variate-value drawn from the binomial distribution.

Specified by:

random in interface Distribution

Overrides:

random in class AbstractDistribution

Returns:

the random variate-value.

setN

public void setN(long n)

Change the "number of trials" parameter.

Parameters:

n - the "number of trials" parameter; must be greater than 0.

Throws:

IllegalArgumentException - if n less than 1.

setP

public void setP(double p)

Change the "probability of success" parameter.

Parameters:

p - the "probability of success" parameter; must be greater than 0 and less than 1.

Throws:

IllegalArgumentException - if p not in (0,1).

toString

public String toString()

Overrides:

toString in class Object

variance

public double variance()

Description copied from class: AbstractDiscreteDistribution

Return variance of the distribution. Note that this method calculates the mean by calling mean(); so if the mean is already calculated, it is more efficient to call moment(2,mean) than use this method. The variance is usually known in terms of the distribution's parameters, so this method should be overridden.

Specified by:

variance in interface Distribution

Overrides:

variance in class AbstractDiscreteDistribution

Returns:

the variance of the distribution.