sim.util.distribution
Class PoissonSlow

java.lang.Object
  sim.util.distribution.AbstractDistribution
      sim.util.distribution.AbstractDiscreteDistribution
          sim.util.distribution.PoissonSlow

All Implemented Interfaces:

java.io.Serializable

public class PoissonSlow
extends AbstractDiscreteDistribution

Poisson distribution; See the math definition and animated definition.

p(k) = (mean^k / k!) * exp(-mean) for k >= 0.

Valid parameter ranges: mean > 0. Note: if mean <= 0.0 then always returns zero.

Instance methods operate on a user supplied uniform random number generator; they are unsynchronized.

Static methods operate on a default uniform random number generator; they are synchronized.

Implementation: This is a port of RandPoisson used in CLHEP 1.4.0 (C++). CLHEP's implementation, in turn, is based upon "W.H.Press et al., Numerical Recipes in C, Second Edition".

See Also:

Serialized Form

Field Summary

protected double	cached_alxm
protected double	cached_g
protected double	cached_sq
protected static double[]	cof
protected double	mean
protected static double	MEAN_MAX
protected static double	SWITCH_MEAN

Fields inherited from class sim.util.distribution.AbstractDistribution

randomGenerator

Constructor Summary

PoissonSlow(double mean, MersenneTwisterFast randomGenerator)
Constructs a poisson distribution.

Method Summary

static double	logGamma(double xx) Returns the value ln(Gamma(xx) for xx > 0.
int	nextInt() Returns a random number from the distribution.
protected int	nextIntSlow() Returns a random number from the distribution.
void	setMean(double mean) Sets the mean.
java.lang.String	toString() Returns a String representation of the receiver.

Methods inherited from class sim.util.distribution.AbstractDiscreteDistribution

nextDouble

Methods inherited from class sim.util.distribution.AbstractDistribution

apply, apply, getRandomGenerator, setRandomGenerator

Methods inherited from class java.lang.Object

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

Field Detail

mean

protected double mean

cached_sq

protected double cached_sq

cached_alxm

protected double cached_alxm

cached_g

protected double cached_g

MEAN_MAX

protected static final double MEAN_MAX

See Also:

Constant Field Values

SWITCH_MEAN

protected static final double SWITCH_MEAN

See Also:

Constant Field Values

cof

protected static final double[] cof

Constructor Detail

PoissonSlow

public PoissonSlow(double mean,
                   MersenneTwisterFast randomGenerator)

Constructs a poisson distribution. Example: mean=1.0.

Method Detail

logGamma

public static double logGamma(double xx)

Returns the value ln(Gamma(xx) for xx > 0. Full accuracy is obtained for xx > 1. For 0 < xx < 1. the reflection formula (6.1.4) can be used first. (Adapted from Numerical Recipes in C)

nextInt

public int nextInt()

Returns a random number from the distribution.

Specified by:

nextInt in class AbstractDiscreteDistribution

nextIntSlow

protected int nextIntSlow()

Returns a random number from the distribution.

setMean

public void setMean(double mean)

Sets the mean.

toString

public java.lang.String toString()

Returns a String representation of the receiver.

Overrides:

toString in class java.lang.Object