squidpony.squidmath

Class GaussianDistribution

java.lang.Object

squidpony.squidmath.GaussianDistribution

All Implemented Interfaces:

IDistribution

public class GaussianDistribution
extends java.lang.Object
implements IDistribution

An IDistribution that produces double results with a Gaussian (normal) distribution. This means it has no limits in any direction, but is much more likely to produce results close to 0. This now uses the Box-Muller Transform (it previously used the Ziggurat method), which means it relies on trigonometric functions (NumberTools.sin_(double) and NumberTools.cos_(double), which are approximations), square root and logarithm calculations, but it only needs to calculate every other number, and it uses a fixed amount of calls to IRNG.nextDouble() (for every pair of outputs, it makes two calls to nextDouble()).
No argument constructor gives a mean of 0 and standard deviation and variance of 1 for an N(0,1) distribution that Z Score tables are built around. The two-argument constructor allows specifying a different mean and standard deviation. In statistics, mean is also called mu, and standard deviation is sigma squared.
Created by Tommy Ettinger on 11/23/2019, rewritten on 7/30/2020.

Nested Class Summary

Nested classes/interfaces inherited from interface squidpony.squidmath.IDistribution

IDistribution.SimpleDistribution

Field Summary

Fields

Modifier and Type	Field and Description
static GaussianDistribution	instance

Fields inherited from interface squidpony.squidmath.IDistribution

EXCLUSIVE_ONE, EXCLUSIVE_ZERO

Constructor Summary

Constructors

Constructor and Description
GaussianDistribution() Creates a Gaussian (normal) distribution with mean of 0 and standard deviation and variance of 1.
GaussianDistribution(double mean, double standardDeviation) Creates a Gaussian (normal) distribution with specified mean and standard deviation.

Method Summary

Modifier and Type	Method and Description
double	getLowerBound() The lower inclusive bound is negative infinity.
double	getMean() Gets the mean value of this distribution (mu).
double	getUpperBound() The upper inclusive bound is infinity.
double	nextDouble(IRNG rng) Gets a double between IDistribution.getLowerBound() and IDistribution.getUpperBound() that obeys this distribution.

Methods inherited from class java.lang.Object

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

Field Detail

instance

public static final GaussianDistribution instance

Constructor Detail

GaussianDistribution

public GaussianDistribution()

Creates a Gaussian (normal) distribution with mean of 0 and standard deviation and variance of 1. This N(0, 1) probability distribution is what Z Score tables are built around.

GaussianDistribution

public GaussianDistribution(double mean,
                            double standardDeviation)

Creates a Gaussian (normal) distribution with specified mean and standard deviation. In statistics, this means providing the mu and sigma, respectively, for an N(mu, pow(sigma, 2)) distribution.

Parameters:

mean - (equivalent to mu) the value at the center of the distribution; also the most common result

standardDeviation - (equivalent to sigma squared) how far and often values should spread out away from the mean

Method Detail

nextDouble

public double nextDouble(IRNG rng)

Description copied from interface: IDistribution

Gets a double between IDistribution.getLowerBound() and IDistribution.getUpperBound() that obeys this distribution.

Specified by:

nextDouble in interface IDistribution

Parameters:

rng - an IRNG, such as RNG or GWTRNG, that this will get one or more random numbers from

Returns:

a double within the range of IDistribution.getLowerBound() and IDistribution.getUpperBound(), both inclusive

getLowerBound

public double getLowerBound()

The lower inclusive bound is negative infinity.

Specified by:

getLowerBound in interface IDistribution

Returns:

negative infinity

getUpperBound

public double getUpperBound()

The upper inclusive bound is infinity.

Specified by:

getUpperBound in interface IDistribution

Returns:

positive infinity

getMean

public double getMean()

Gets the mean value of this distribution (mu).

Specified by:

getMean in interface IDistribution

Returns:

the mean value of this distribution (mu)