org.apache.commons.math.distribution
Class AbstractIntegerDistribution

java.lang.Object
  org.apache.commons.math.distribution.AbstractDistribution
      org.apache.commons.math.distribution.AbstractIntegerDistribution

All Implemented Interfaces:

Serializable, DiscreteDistribution, Distribution, IntegerDistribution

Direct Known Subclasses:

BinomialDistributionImpl, HypergeometricDistributionImpl, PascalDistributionImpl, PoissonDistributionImpl, ZipfDistributionImpl

public abstract class AbstractIntegerDistribution
extends AbstractDistribution
implements IntegerDistribution, Serializable

Base class for integer-valued discrete distributions. Default implementations are provided for some of the methods that do not vary from distribution to distribution.

Version:

$Revision: 1067494 $ $Date: 2011-02-05 20:49:07 +0100 (sam. 05 févr. 2011) $

See Also:

Serialized Form

Field Summary

protected RandomDataImpl

randomData RandomData instance used to generate samples from the distribution

Constructor Summary

protected

AbstractIntegerDistribution() Default constructor.

Method Summary

double	cumulativeProbability(double x) For a random variable X whose values are distributed according to this distribution, this method returns P(X ≤ x).
double	cumulativeProbability(double x0, double x1) For a random variable X whose values are distributed according to this distribution, this method returns P(x0 ≤ X ≤ x1).
abstract double	cumulativeProbability(int x) For a random variable X whose values are distributed according to this distribution, this method returns P(X ≤ x).
double	cumulativeProbability(int x0, int x1) For a random variable X whose values are distributed according to this distribution, this method returns P(x0 ≤ X ≤ x1).
protected abstract int	getDomainLowerBound(double p) Access the domain value lower bound, based on p, used to bracket a PDF root.
protected abstract int	getDomainUpperBound(double p) Access the domain value upper bound, based on p, used to bracket a PDF root.
int	inverseCumulativeProbability(double p) For a random variable X whose values are distributed according to this distribution, this method returns the largest x, such that P(X ≤ x) ≤ p.
boolean	isSupportLowerBoundInclusive() Use this method to get information about whether the lower bound of the support is inclusive or not.
boolean	isSupportUpperBoundInclusive() Use this method to get information about whether the upper bound of the support is inclusive or not.
double	probability(double x) For a random variable X whose values are distributed according to this distribution, this method returns P(X = x).
void	reseedRandomGenerator(long seed) Reseeds the random generator used to generate samples.
int	sample() Generates a random value sampled from this distribution.
int[]	sample(int sampleSize) Generates a random sample from the distribution.

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

probability

Field Detail

randomData

protected final RandomDataImpl randomData

RandomData instance used to generate samples from the distribution

Since:

2.2

Constructor Detail

AbstractIntegerDistribution

protected AbstractIntegerDistribution()

Default constructor.

Method Detail

cumulativeProbability

public double cumulativeProbability(double x)
                             throws MathException

For a random variable X whose values are distributed according to this distribution, this method returns P(X ≤ x). In other words, this method represents the (cumulative) distribution function, or CDF, for this distribution.

If x does not represent an integer value, the CDF is evaluated at the greatest integer less than x.

Specified by:

cumulativeProbability in interface Distribution

Parameters:

x - the value at which the distribution function is evaluated.

Returns:

cumulative probability that a random variable with this distribution takes a value less than or equal to x

Throws:

MathException - if the cumulative probability can not be computed due to convergence or other numerical errors.

cumulativeProbability

public double cumulativeProbability(double x0,
                                    double x1)
                             throws MathException

For a random variable X whose values are distributed according to this distribution, this method returns P(x0 ≤ X ≤ x1).

Specified by:

cumulativeProbability in interface Distribution

Overrides:

cumulativeProbability in class AbstractDistribution

Parameters:

x0 - the (inclusive) lower bound

x1 - the (inclusive) upper bound

Returns:

the probability that a random variable with this distribution will take a value between x0 and x1, including the endpoints.

Throws:

MathException - if the cumulative probability can not be computed due to convergence or other numerical errors.

IllegalArgumentException - if x0 > x1

cumulativeProbability

public abstract double cumulativeProbability(int x)
                                      throws MathException

For a random variable X whose values are distributed according to this distribution, this method returns P(X ≤ x). In other words, this method represents the probability distribution function, or PDF, for this distribution.

Specified by:

cumulativeProbability in interface IntegerDistribution

Parameters:

x - the value at which the PDF is evaluated.

Returns:

PDF for this distribution.

Throws:

MathException - if the cumulative probability can not be computed due to convergence or other numerical errors.

probability

public double probability(double x)

For a random variable X whose values are distributed according to this distribution, this method returns P(X = x). In other words, this method represents the probability mass function, or PMF, for the distribution.

If x does not represent an integer value, 0 is returned.

Specified by:

probability in interface DiscreteDistribution

Parameters:

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

Returns:

the value of the probability density function at x

cumulativeProbability

public double cumulativeProbability(int x0,
                                    int x1)
                             throws MathException

For a random variable X whose values are distributed according to this distribution, this method returns P(x0 ≤ X ≤ x1).

Specified by:

cumulativeProbability in interface IntegerDistribution

Parameters:

x0 - the inclusive, lower bound

x1 - the inclusive, upper bound

Returns:

the cumulative probability.

Throws:

MathException - if the cumulative probability can not be computed due to convergence or other numerical errors.

IllegalArgumentException - if x0 > x1

inverseCumulativeProbability

public int inverseCumulativeProbability(double p)
                                 throws MathException

For a random variable X whose values are distributed according to this distribution, this method returns the largest x, such that P(X ≤ x) ≤ p.

Specified by:

inverseCumulativeProbability in interface IntegerDistribution

Parameters:

p - the desired probability

Returns:

the largest x such that P(X ≤ x) <= p

Throws:

MathException - if the inverse cumulative probability can not be computed due to convergence or other numerical errors.

IllegalArgumentException - if p < 0 or p > 1

reseedRandomGenerator

public void reseedRandomGenerator(long seed)

Reseeds the random generator used to generate samples.

Parameters:

seed - the new seed

Since:

2.2

sample

public int sample()
           throws MathException

Generates a random value sampled from this distribution. The default implementation uses the inversion method.

Returns:

random value

Throws:

MathException - if an error occurs generating the random value

Since:

2.2

sample

public int[] sample(int sampleSize)
             throws MathException

Generates a random sample from the distribution. The default implementation generates the sample by calling sample() in a loop.

Parameters:

sampleSize - number of random values to generate

Returns:

an array representing the random sample

Throws:

MathException - if an error occurs generating the sample

IllegalArgumentException - if sampleSize is not positive

Since:

2.2

getDomainLowerBound

protected abstract int getDomainLowerBound(double p)

Access the domain value lower bound, based on p, used to bracket a PDF root. This method is used by inverseCumulativeProbability(double) to find critical values.

Parameters:

p - the desired probability for the critical value

Returns:

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

getDomainUpperBound

protected abstract int getDomainUpperBound(double p)

Access the domain value upper bound, based on p, used to bracket a PDF root. This method is used by inverseCumulativeProbability(double) to find critical values.

Parameters:

p - the desired probability for the critical value

Returns:

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

isSupportLowerBoundInclusive

public boolean isSupportLowerBoundInclusive()

Use this method to get information about whether the lower bound of the support is inclusive or not. For discrete support, only true here is meaningful.

Returns:

true (always but at Integer.MIN_VALUE because of the nature of discrete support)

Since:

2.2

isSupportUpperBoundInclusive

public boolean isSupportUpperBoundInclusive()

Use this method to get information about whether the upper bound of the support is inclusive or not. For discrete support, only true here is meaningful.

Returns:

true (always but at Integer.MAX_VALUE because of the nature of discrete support)

Since:

2.2