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

Class DiscreteUniformSampler

java.lang.Object

org.apache.commons.rng.sampling.distribution.SamplerBase

org.apache.commons.rng.sampling.distribution.DiscreteUniformSampler

All Implemented Interfaces:

DiscreteSampler, SharedStateDiscreteSampler, SharedStateSampler<SharedStateDiscreteSampler>

public class DiscreteUniformSampler
extends SamplerBase
implements SharedStateDiscreteSampler

Discrete uniform distribution sampler.

Sampling uses UniformRandomProvider.nextInt().

When the range is a power of two the number of calls is 1 per sample. Otherwise a rejection algorithm is used to ensure uniformity. In the worst case scenario where the range spans half the range of an int (2³¹ + 1) the expected number of calls is 2 per sample.

This sampler can be used as a replacement for UniformRandomProvider.nextInt() with appropriate adjustment of the upper bound to be inclusive and will outperform that method when the range is not a power of two. The advantage is gained by pre-computation of the rejection threshold.

The sampling algorithm is described in:

Lemire, D (2019). Fast Random Integer Generation in an Interval. ACM Transactions on Modeling and Computer Simulation 29 (1).

The number of int values required per sample follows a geometric distribution with a probability of success p of 1 - ((2^32 % n) / 2^32). This requires on average 1/p random int values per sample.

Since:

1.0

See Also:

Fast Random Integer Generation in an Interval

Constructor Summary

Constructors

Constructor	Description
DiscreteUniformSampler(UniformRandomProvider rng, int lower, int upper)	This instance delegates sampling.

Method Summary

Modifier and Type	Method	Description
static SharedStateDiscreteSampler	of(UniformRandomProvider rng, int lower, int upper)	Creates a new discrete uniform distribution sampler.
int	sample()	Creates a sample.
String	toString()
SharedStateDiscreteSampler	withUniformRandomProvider(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 org.apache.commons.rng.sampling.distribution.SamplerBase

nextDouble, nextInt, nextInt, nextLong

Methods inherited from class java.lang.Object

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

Constructor Detail

DiscreteUniformSampler

public DiscreteUniformSampler(UniformRandomProvider rng,
                              int lower,
                              int upper)

This instance delegates sampling. Use the factory method of(UniformRandomProvider, int, int) to create an optimal sampler.

Parameters:

rng - Generator of uniformly distributed random numbers.

lower - Lower bound (inclusive) of the distribution.

upper - Upper bound (inclusive) of the distribution.

Throws:

IllegalArgumentException - if lower > upper.

Method Detail

sample

public int sample()

Creates a sample.

Specified by:

sample in interface DiscreteSampler

Returns:

a sample.

toString

public String toString()

Overrides:

toString in class SamplerBase

withUniformRandomProvider

public SharedStateDiscreteSampler withUniformRandomProvider(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

Since:

1.3

of

public static SharedStateDiscreteSampler of(UniformRandomProvider rng,
                                            int lower,
                                            int upper)

Creates a new discrete uniform distribution sampler.

Parameters:

rng - Generator of uniformly distributed random numbers.

lower - Lower bound (inclusive) of the distribution.

upper - Upper bound (inclusive) of the distribution.

Returns:

the sampler

Throws:

IllegalArgumentException - if lower > upper.

Since:

1.3