org.apache.commons.math.distribution

Class ZipfDistributionImpl

java.lang.Object

org.apache.commons.math.distribution.AbstractDistribution

org.apache.commons.math.distribution.AbstractIntegerDistribution

org.apache.commons.math.distribution.ZipfDistributionImpl

All Implemented Interfaces:

java.io.Serializable, DiscreteDistribution, Distribution, IntegerDistribution, ZipfDistribution

public class ZipfDistributionImpl
extends AbstractIntegerDistribution
implements ZipfDistribution, java.io.Serializable

Implementation for the ZipfDistribution.

Version:

$Revision: 1054524 $ $Date: 2011-01-03 05:59:18 +0100 (lun. 03 janv. 2011) $

See Also:

Serialized Form

Field Summary

Fields

Modifier and Type	Field and Description
private double	exponent Exponent parameter of the distribution.
private int	numberOfElements Number of elements.
private static long	serialVersionUID Serializable version identifier.

Fields inherited from class org.apache.commons.math.distribution.AbstractIntegerDistribution

randomData

Constructor Summary

Constructors

Constructor and Description
ZipfDistributionImpl(int numberOfElements, double exponent) Create a new Zipf distribution with the given number of elements and exponent.

Method Summary

Methods

Modifier and Type	Method and Description
double	cumulativeProbability(int x) The probability distribution function P(X <= x) for a Zipf distribution.
private double	generalizedHarmonic(int n, double m) Calculates the Nth generalized harmonic number.
protected int	getDomainLowerBound(double p) Access the domain value lower bound, based on p, used to bracket a PDF root.
protected int	getDomainUpperBound(double p) Access the domain value upper bound, based on p, used to bracket a PDF root.
double	getExponent() Get the exponent characterising the distribution.
int	getNumberOfElements() Get the number of elements (e.g.
protected double	getNumericalMean() Returns the mean.
protected double	getNumericalVariance() Returns the variance.
int	getSupportLowerBound() Returns the lower bound of the support for the distribution.
int	getSupportUpperBound() Returns the upper bound of the support for the distribution.
double	probability(int x) The probability mass function P(X = x) for a Zipf distribution.
void	setExponent(double s) Deprecated. as of 2.1 (class will become immutable in 3.0)
private void	setExponentInternal(double s) Set the exponent characterising the distribution.
void	setNumberOfElements(int n) Deprecated. as of 2.1 (class will become immutable in 3.0)
private void	setNumberOfElementsInternal(int n) Set the number of elements (e.g.

Methods inherited from class org.apache.commons.math.distribution.AbstractIntegerDistribution

cumulativeProbability, cumulativeProbability, cumulativeProbability, inverseCumulativeProbability, isSupportLowerBoundInclusive, isSupportUpperBoundInclusive, probability, reseedRandomGenerator, sample, sample

Methods inherited from class java.lang.Object

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

Methods inherited from interface org.apache.commons.math.distribution.IntegerDistribution

cumulativeProbability, inverseCumulativeProbability

Methods inherited from interface org.apache.commons.math.distribution.DiscreteDistribution

probability

Methods inherited from interface org.apache.commons.math.distribution.Distribution

cumulativeProbability, cumulativeProbability

Field Detail

serialVersionUID

private static final long serialVersionUID

Serializable version identifier.

See Also:

Constant Field Values

numberOfElements

private int numberOfElements

Number of elements.

exponent

private double exponent

Exponent parameter of the distribution.

Constructor Detail

ZipfDistributionImpl

public ZipfDistributionImpl(int numberOfElements,
                    double exponent)
                     throws java.lang.IllegalArgumentException

Create a new Zipf distribution with the given number of elements and exponent. Both values must be positive; otherwise an IllegalArgumentException is thrown.

Parameters:

numberOfElements - the number of elements

exponent - the exponent

Throws:

java.lang.IllegalArgumentException - if n ≤ 0 or s ≤ 0.0

Method Detail

getNumberOfElements

public int getNumberOfElements()

Get the number of elements (e.g. corpus size) for the distribution.

Specified by:

getNumberOfElements in interface ZipfDistribution

Returns:

the number of elements

setNumberOfElements

@Deprecated
public void setNumberOfElements(int n)

Deprecated. as of 2.1 (class will become immutable in 3.0)

Set the number of elements (e.g. corpus size) for the distribution. The parameter value must be positive; otherwise an IllegalArgumentException is thrown.

Specified by:

setNumberOfElements in interface ZipfDistribution

Parameters:

n - the number of elements

Throws:

java.lang.IllegalArgumentException - if n ≤ 0

setNumberOfElementsInternal

private void setNumberOfElementsInternal(int n)
                                  throws java.lang.IllegalArgumentException

Set the number of elements (e.g. corpus size) for the distribution. The parameter value must be positive; otherwise an IllegalArgumentException is thrown.

Parameters:

n - the number of elements

Throws:

java.lang.IllegalArgumentException - if n ≤ 0

getExponent

public double getExponent()

Get the exponent characterising the distribution.

Specified by:

getExponent in interface ZipfDistribution

Returns:

the exponent

setExponent

@Deprecated
public void setExponent(double s)

Deprecated. as of 2.1 (class will become immutable in 3.0)

Set the exponent characterising the distribution. The parameter value must be positive; otherwise an IllegalArgumentException is thrown.

Specified by:

setExponent in interface ZipfDistribution

Parameters:

s - the exponent

Throws:

java.lang.IllegalArgumentException - if s ≤ 0.0

setExponentInternal

private void setExponentInternal(double s)
                          throws java.lang.IllegalArgumentException

Set the exponent characterising the distribution. The parameter value must be positive; otherwise an IllegalArgumentException is thrown.

Parameters:

s - the exponent

Throws:

java.lang.IllegalArgumentException - if s ≤ 0.0

probability

public double probability(int x)

The probability mass function P(X = x) for a Zipf distribution.

Specified by:

probability in interface IntegerDistribution

Parameters:

x - the value at which the probability density function is evaluated.

Returns:

the value of the probability mass function at x

cumulativeProbability

public double cumulativeProbability(int x)

The probability distribution function P(X <= x) for a Zipf distribution.

Specified by:

cumulativeProbability in interface IntegerDistribution

Specified by:

cumulativeProbability in class AbstractIntegerDistribution

Parameters:

x - the value at which the PDF is evaluated.

Returns:

Zipf distribution function evaluated at x

getDomainLowerBound

protected int getDomainLowerBound(double p)

Access the domain value lower bound, based on p, used to bracket a PDF root.

Specified by:

getDomainLowerBound in class AbstractIntegerDistribution

Parameters:

p - the desired probability for the critical value

Returns:

domain value lower bound, i.e. P(X < lower bound) < p

getDomainUpperBound

protected int getDomainUpperBound(double p)

Access the domain value upper bound, based on p, used to bracket a PDF root.

Specified by:

getDomainUpperBound in class AbstractIntegerDistribution

Parameters:

p - the desired probability for the critical value

Returns:

domain value upper bound, i.e. P(X < upper bound) > p

generalizedHarmonic

private double generalizedHarmonic(int n,
                         double m)

Calculates the Nth generalized harmonic number. See Harmonic Series.

Parameters:

n - the term in the series to calculate (must be ≥ 1)

m - the exponent; special case m == 1.0 is the harmonic series

Returns:

the nth generalized harmonic number

getSupportLowerBound

public int getSupportLowerBound()

Returns the lower bound of the support for the distribution. The lower bound of the support is always 1 no matter the parameters.

Returns:

lower bound of the support (always 1)

Since:

2.2

getSupportUpperBound

public int getSupportUpperBound()

Returns the upper bound of the support for the distribution. The upper bound of the support is the number of elements

Returns:

upper bound of the support

Since:

2.2

getNumericalMean

protected double getNumericalMean()

Returns the mean. For number of elements N and exponent s, the mean is Hs1 / Hs where

• Hs1 = generalizedHarmonic(N, s - 1)
• Hs = generalizedHarmonic(N, s)

Returns:

the mean

Since:

2.2

getNumericalVariance

protected double getNumericalVariance()

Returns the variance. For number of elements N and exponent s, the mean is (Hs2 / Hs) - (Hs1^2 / Hs^2) where

• Hs2 = generalizedHarmonic(N, s - 2)
• Hs1 = generalizedHarmonic(N, s - 1)
• Hs = generalizedHarmonic(N, s)

Returns:

the variance

Since:

2.2