Package org.apache.commons.rng.sampling.distribution

Class KempSmallMeanPoissonSampler

java.lang.Object

org.apache.commons.rng.sampling.distribution.KempSmallMeanPoissonSampler

All Implemented Interfaces:

DiscreteSampler, SharedStateDiscreteSampler, SharedStateSampler<SharedStateDiscreteSampler>

public final class KempSmallMeanPoissonSampler
extends java.lang.Object
implements SharedStateDiscreteSampler

Sampler for the Poisson distribution.

• Kemp, A, W, (1981) Efficient Generation of Logarithmically Distributed Pseudo-Random Variables. Journal of the Royal Statistical Society. Vol. 30, No. 3, pp. 249-253.

This sampler is suitable for mean < 40. For large means, LargeMeanPoissonSampler should be used instead.

Note: The algorithm uses a recurrence relation to compute the Poisson probability and a rolling summation for the cumulative probability. When the mean is large the initial probability (Math.exp(-mean)) is zero and an exception is raised by the constructor.

Sampling uses 1 call to UniformRandomProvider.nextDouble(). This method provides an alternative to the SmallMeanPoissonSampler for slow generators of double.

Since:

1.3

See Also:

Kemp, A.W. (1981) JRSS Vol. 30, pp. 249-253

Method Summary

Modifier and Type	Method	Description
static SharedStateDiscreteSampler	of(org.apache.commons.rng.UniformRandomProvider rng, double mean)	Creates a new sampler for the Poisson distribution.
int	sample()	Creates a sample.
java.lang.String	toString()
SharedStateDiscreteSampler	withUniformRandomProvider(org.apache.commons.rng.UniformRandomProvider rng)	Create a new instance of the sampler with the same underlying state using the given uniform random provider as the source of randomness.

Methods inherited from class java.lang.Object

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

Method Detail

sample

public int sample()

Creates a sample.

Specified by:

sample in interface DiscreteSampler

Returns:

a sample.

toString

public java.lang.String toString()

Overrides:

toString in class java.lang.Object

withUniformRandomProvider

public SharedStateDiscreteSampler withUniformRandomProvider(org.apache.commons.rng.UniformRandomProvider rng)

Create a new instance of the sampler with the same underlying state using the given uniform random provider as the source of randomness.

Specified by:

withUniformRandomProvider in interface SharedStateSampler<SharedStateDiscreteSampler>

Parameters:

rng - Generator of uniformly distributed random numbers.

Returns:

the sampler

of

public static SharedStateDiscreteSampler of(org.apache.commons.rng.UniformRandomProvider rng,
                                            double mean)

Creates a new sampler for the Poisson distribution.

Parameters:

rng - Generator of uniformly distributed random numbers.

mean - Mean of the distribution.

Returns:

the sampler

Throws:

java.lang.IllegalArgumentException - if mean <= 0 or Math.exp(-mean) == 0.