java.lang.Object

gaiasky.util.math.StdRandom

public final class StdRandom
extends java.lang.Object

The StdRandom class provides static methods for generating random number from various discrete and continuous distributions, including Bernoulli, uniform, Gaussian, exponential, pareto, Poisson, and Cauchy. It also provides method for shuffling an array or subarray.

For additional documentation, see Section 2.2 of Introduction to Programming in Java: An Interdisciplinary Approach by Robert Sedgewick and Kevin Wayne.

Method Summary

Modifier and Type	Method	Description
`static boolean`	`bernoulli()`	Returns a random boolean from a Bernoulli distribution with success probability 1/2.
`static boolean`	`bernoulli(double p)`	Returns a random boolean from a Bernoulli distribution with success probability p.
`static double`	`beta(double alpha, double beta)`	Returns a random real number from a beta distribution with parameters α and β.
`static double`	`cauchy()`	Returns a random real number from the Cauchy distribution.
`static int`	`discrete(double[] probabilities)`	Returns a random integer from the specified discrete distribution.
`static int`	`discrete(int[] frequencies)`	Returns a random integer from the specified discrete distribution.
`static double`	`exp(double lambda)`	Returns a random real number from an exponential distribution with rate λ.
`static double`	`gaussian()`	Returns a random real number from a standard Gaussian distribution.
`static double`	`gaussian(double mu, double sigma)`	Returns a random real number from a Gaussian distribution with mean μ and standard deviation σ.
`static int`	`geometric(double p)`	Returns a random integer from a geometric distribution with success probability p.
`static long`	`getSeed()`	Returns the seed of the pseudorandom number generator.
`static double`	`pareto()`	Returns a random real number from the standard Pareto distribution.
`static double`	`pareto(double alpha)`	Returns a random real number from a Pareto distribution with shape parameter α.
`static int`	`poisson(double lambda)`	Returns a random integer from a Poisson distribution with mean λ.
`static double`	`random()`	Deprecated. Replaced by `uniform()`.
`static void`	`setSeed(long s)`	Sets the seed of the pseudorandom number generator.
`static void`	`shuffle(double[] a)`	Rearranges the elements of the specified array in uniformly random order.
`static void`	`shuffle(double[] a, int lo, int hi)`	Rearranges the elements of the specified subarray in uniformly random order.
`static void`	`shuffle(int[] a)`	Rearranges the elements of the specified array in uniformly random order.
`static void`	`shuffle(int[] a, int lo, int hi)`	Rearranges the elements of the specified subarray in uniformly random order.
`static void`	`shuffle(java.lang.Object[] a)`	Rearranges the elements of the specified array in uniformly random order.
`static void`	`shuffle(java.lang.Object[] a, int lo, int hi)`	Rearranges the elements of the specified subarray in uniformly random order.
`static double`	`uniform()`	Returns a random real number uniformly in [0, 1).
`static double`	`uniform(double a, double b)`	Returns a random real number uniformly in [a, b).
`static int`	`uniform(int n)`	Returns a random integer uniformly in [0, n).
`static int`	`uniform(int a, int b)`	Returns a random integer uniformly in [a, b).

Methods inherited from class java.lang.Object

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

Method Details
- setSeed
  
  public static void setSeed(long s)
  
  Sets the seed of the pseudorandom number generator. This method enables you to produce the same sequence of "random" number for each execution of the program. Ordinarily, you should call this method at most once per program.
  
  Parameters:
  
  s - the seed
- getSeed
  
  public static long getSeed()
  
  Returns the seed of the pseudorandom number generator.
  
  Returns:
  
  the seed
- uniform
  
  public static double uniform()
  
  Returns a random real number uniformly in [0, 1).
  
  Returns:
  
  a random real number uniformly in [0, 1)
- uniform
  
  public static int uniform(int n)
  
  Returns a random integer uniformly in [0, n).
  
  Parameters:
  
  n - number of possible integers
  
  Returns:
  
  a random integer uniformly between 0 (inclusive) and N (exclusive)
  
  Throws:
  
  java.lang.IllegalArgumentException - if n <= 0
- random
  
  @Deprecated public static double random()
  
  Deprecated.
  Replaced by uniform().
  
  Returns a random real number uniformly in [0, 1).
  
  Returns:
  
  a random real number uniformly in [0, 1)
- uniform
  
  public static int uniform(int a, int b)
  
  Returns a random integer uniformly in [a, b).
  
  Parameters:
  
  a - the left endpoint
  
  b - the right endpoint
  
  Returns:
  
  a random integer uniformly in [a, b)
  
  Throws:
  
  java.lang.IllegalArgumentException - if b <= a
  
  java.lang.IllegalArgumentException - if b - a >= Integer.MAX_VALUE
- uniform
  
  public static double uniform(double a, double b)
  
  Returns a random real number uniformly in [a, b).
  
  Parameters:
  
  a - the left endpoint
  
  b - the right endpoint
  
  Returns:
  
  a random real number uniformly in [a, b)
  
  Throws:
  
  java.lang.IllegalArgumentException - unless a < b
- bernoulli
  
  public static boolean bernoulli(double p)
  
  Returns a random boolean from a Bernoulli distribution with success probability p.
  
  Parameters:
  
  p - the probability of returning true
  
  Returns:
  
  true with probability p and false with probability p
  
  Throws:
  
  java.lang.IllegalArgumentException - unless p >= 0.0 and p <= 1.0
- bernoulli
  
  public static boolean bernoulli()
  
  Returns a random boolean from a Bernoulli distribution with success probability 1/2.
  
  Returns:
  
  true with probability 1/2 and false with probability 1/2
- gaussian
  
  public static double gaussian()
  
  Returns a random real number from a standard Gaussian distribution.
  
  Returns:
  
  a random real number from a standard Gaussian distribution (mean 0 and standard deviation 1).
- gaussian
  
  public static double gaussian(double mu, double sigma)
  
  Returns a random real number from a Gaussian distribution with mean μ and standard deviation σ.
  
  Parameters:
  
  mu - the mean
  
  sigma - the standard deviation
  
  Returns:
  
  a real number distributed according to the Gaussian distribution with mean mu and standard deviation sigma
- geometric
  
  public static int geometric(double p)
  
  Returns a random integer from a geometric distribution with success probability p.
  
  Parameters:
  
  p - the parameter of the geometric distribution
  
  Returns:
  
  a random integer from a geometric distribution with success probability p; or Integer.MAX_VALUE if p is (nearly) equal to 1.0.
  
  Throws:
  
  java.lang.IllegalArgumentException - unless p >= 0.0 and p <= 1.0
- poisson
  
  public static int poisson(double lambda)
  
  Returns a random integer from a Poisson distribution with mean λ.
  
  Parameters:
  
  lambda - the mean of the Poisson distribution
  
  Returns:
  
  a random integer from a Poisson distribution with mean lambda
  
  Throws:
  
  java.lang.IllegalArgumentException - unless lambda > 0.0 and not infinite
- pareto
  
  public static double pareto()
  
  Returns a random real number from the standard Pareto distribution.
  
  Returns:
  
  a random real number from the standard Pareto distribution
- pareto
  
  public static double pareto(double alpha)
  
  Returns a random real number from a Pareto distribution with shape parameter α.
  
  Parameters:
  
  alpha - shape parameter
  
  Returns:
  
  a random real number from a Pareto distribution with shape parameter alpha
  
  Throws:
  
  java.lang.IllegalArgumentException - unless alpha > 0.0
- cauchy
  
  public static double cauchy()
  
  Returns a random real number from the Cauchy distribution.
  
  Returns:
  
  a random real number from the Cauchy distribution.
- discrete
  
  public static int discrete(double[] probabilities)
  
  Returns a random integer from the specified discrete distribution.
  
  Parameters:
  
  probabilities - the probability of occurrence of each integer
  
  Returns:
  
  a random integer from a discrete distribution: i with probability probabilities[i]
  
  Throws:
  
  java.lang.NullPointerException - if probabilities is null
  
  java.lang.IllegalArgumentException - if sum of array entries is not (very nearly) equal to 1.0
  
  java.lang.IllegalArgumentException - unless probabilities[i] >= 0.0 for each index i
- discrete
  
  public static int discrete(int[] frequencies)
  
  Returns a random integer from the specified discrete distribution.
  
  Parameters:
  
  frequencies - the frequency of occurrence of each integer
  
  Returns:
  
  a random integer from a discrete distribution: i with probability proportional to frequencies[i]
  
  Throws:
  
  java.lang.NullPointerException - if frequencies is null
  
  java.lang.IllegalArgumentException - if all array entries are 0
  
  java.lang.IllegalArgumentException - if frequencies[i] is negative for any index i
  
  java.lang.IllegalArgumentException - if sum of frequencies exceeds Integer.MAX_VALUE (2³¹ - 1)
- exp
  
  public static double exp(double lambda)
  
  Returns a random real number from an exponential distribution with rate λ.
  
  Parameters:
  
  lambda - the rate of the exponential distribution
  
  Returns:
  
  a random real number from an exponential distribution with rate lambda
  
  Throws:
  
  java.lang.IllegalArgumentException - unless lambda > 0.0
- beta
  
  public static double beta(double alpha, double beta)
  
  Returns a random real number from a beta distribution with parameters α and β. The result is normalized in [-1,1]
  
  Parameters:
  
  alpha - the shape parameter α
  
  beta - the shape parameter β
  
  Returns:
  
  a random real number from a beta distribution normalized in [-1,1]
  
  Throws:
  
  java.lang.IllegalArgumentException - unless alpha, beta > 0.0
- shuffle
  
  public static void shuffle(java.lang.Object[] a)
  
  Rearranges the elements of the specified array in uniformly random order.
  
  Parameters:
  
  a - the array to shuffle
  
  Throws:
  
  java.lang.NullPointerException - if a is null
- shuffle
  
  public static void shuffle(double[] a)
  
  Rearranges the elements of the specified array in uniformly random order.
  
  Parameters:
  
  a - the array to shuffle
  
  Throws:
  
  java.lang.NullPointerException - if a is null
- shuffle
  
  public static void shuffle(int[] a)
  
  Rearranges the elements of the specified array in uniformly random order.
  
  Parameters:
  
  a - the array to shuffle
  
  Throws:
  
  java.lang.NullPointerException - if a is null
- shuffle
  
  public static void shuffle(java.lang.Object[] a, int lo, int hi)
  
  Rearranges the elements of the specified subarray in uniformly random order.
  
  Parameters:
  
  a - the array to shuffle
  
  lo - the left endpoint (inclusive)
  
  hi - the right endpoint (inclusive)
  
  Throws:
  
  java.lang.NullPointerException - if a is null
  
  java.lang.IndexOutOfBoundsException - unless (0 <= lo) && (lo <= hi) && (hi < a.length)
- shuffle
  
  public static void shuffle(double[] a, int lo, int hi)
  
  Rearranges the elements of the specified subarray in uniformly random order.
  
  Parameters:
  
  a - the array to shuffle
  
  lo - the left endpoint (inclusive)
  
  hi - the right endpoint (inclusive)
  
  Throws:
  
  java.lang.NullPointerException - if a is null
  
  java.lang.IndexOutOfBoundsException - unless (0 <= lo) && (lo <= hi) && (hi < a.length)
- shuffle
  
  public static void shuffle(int[] a, int lo, int hi)
  
  Rearranges the elements of the specified subarray in uniformly random order.
  
  Parameters:
  
  a - the array to shuffle
  
  lo - the left endpoint (inclusive)
  
  hi - the right endpoint (inclusive)
  
  Throws:
  
  java.lang.NullPointerException - if a is null
  
  java.lang.IndexOutOfBoundsException - unless (0 <= lo) && (lo <= hi) && (hi < a.length)

Class StdRandom

Method Summary

Methods inherited from class java.lang.Object

Method Details

setSeed

getSeed

uniform

uniform

random

uniform

uniform

bernoulli

bernoulli

gaussian

gaussian

geometric

poisson

pareto

pareto

cauchy

discrete

discrete

exp

beta

shuffle

shuffle

shuffle

shuffle

shuffle

shuffle