sdsu.algorithms.data
Class Zipf

java.lang.Object
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  +--sdsu.algorithms.data.ProbabilityDistribution
        |
        +--sdsu.algorithms.data.DiscreteProbability
              |
              +--sdsu.algorithms.data.NoInverseDistribution
                    |
                    +--sdsu.algorithms.data.Zipf

public class Zipf

extends NoInverseDistribution

The Zipfian distribution models the frequency of the word usage in written English and the population of U.S. cities (amoung other things). When ranked by frequency, the frequency of the i'th is proportional to the frquency of the first item divided by i. Reference: Handbook of Algorithms and Data Structures, G. H. Gonnet, Addison-Wesley, 1984, pp 203.

Version:

1.0 11 June 1997

Author:

Roger Whitney (whitney@cs.sdsu.edu)

Constructor Summary

Zipf(int populationSize)
Returns a Zipf distribution.

Method Summary

double	density(double sampleSpaceItem) Returns the probability of an item in the sample space will occur.
double	mean() Returns the mean of the Bernoulli distribution
double	variance() Returns the variance of the probability distribution

Methods inherited from class sdsu.algorithms.data.NoInverseDistribution

nextElement

Methods inherited from class sdsu.algorithms.data.DiscreteProbability

distribution

Methods inherited from class sdsu.algorithms.data.ProbabilityDistribution

density

Methods inherited from class java.lang.Object

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

Constructor Detail

Zipf

public Zipf(int populationSize)

Returns a Zipf distribution.

Parameters:

populationSize - number of elements in the sample space.

Throws:

OutOfBoundsException - thrown if populationSize is not greater than zero.

Method Detail

density

public double density(double sampleSpaceItem)
               throws OutOfBoundsException

Returns the probability of an item in the sample space will occur. sampleSpaceItem must be either 0 or 1.

Parameters:

sampleSpaceItem - an integer value in the interval [1, populationSize]. Is cast to int in density.

Throws:

OutOfBoundsException - thrown if sampleSpaceItem is not either 0 or 1.

Overrides:

density in class ProbabilityDistribution

mean

public double mean()

Returns the mean of the Bernoulli distribution

Overrides:

mean in class ProbabilityDistribution

variance

public double variance()

Returns the variance of the probability distribution

Overrides:

variance in class ProbabilityDistribution