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rand Pseudo random number generation.

This module provides a random number generator. The module contains a number of algorithms. The uniform distribution algorithms use the scrambled Xorshift algorithms by Sebastiano Vigna. The normal distribution algorithm uses the Ziggurat Method by Marsaglia and Tsang.

For some algorithms, jump functions are provided for generating non-overlapping sequences for parallel computations. The jump functions perform calculations equivalent to perform a large number of repeated calls for calculating new states.

The following algorithms are provided:

exsplus

Xorshift116+, 58 bits precision and period of 2^116-1

Jump function: equivalent to 2^64 calls

 exs64

Xorshift64*, 64 bits precision and a period of 2^64-1

Jump function: not available

 exs1024

Xorshift1024*, 64 bits precision and a period of 2^1024-1

Jump function: equivalent to 2^512 calls

The default algorithm is exsplus. If a specific algorithm is required, ensure to always use seed/1 to initialize the state.

Every time a random number is requested, a state is used to calculate it and a new state is produced. The state can either be implicit or be an explicit argument and return value.

The functions with implicit state use the process dictionary variable rand_seed to remember the current state.

If a process calls uniform/0 or uniform/1 without setting a seed first, seed/1 is called automatically with the default algorithm and creates a non-constant seed.

The functions with explicit state never use the process dictionary.

Examples:

Simple use; creates and seeds the default algorithm with a non-constant seed if not already done:

R0 = rand:uniform(),
R1 = rand:uniform(),

Use a specified algorithm:

_ = rand:seed(exs1024),
R2 = rand:uniform(),

Use a specified algorithm with a constant seed:

_ = rand:seed(exs1024, {123, 123534, 345345}),
R3 = rand:uniform(),

Use the functional API with a non-constant seed:

S0 = rand:seed_s(exsplus),
{R4, S1} = rand:uniform_s(S0),

Create a standard normal deviate:

{SND0, S2} = rand:normal_s(S1),

This random number generator is not cryptographically strong. If a strong cryptographic random number generator is needed, use one of functions in the crypto module, for example, crypto:strong_rand_bytes/1.

Algorithm-dependent state.

Algorithm-dependent state that can be printed or saved to file.

 Export the random number generation state.

Returns the random number state in an external format. To be used with seed/1.

 Export the random number generation state.

Returns the random number generator state in an external format. To be used with seed/1.

 Return the seed after performing jump calculation to the state in the process dictionary.

Returns the state after performing jump calculation to the state in the process dictionary.

This function generates a not_implemented error exception when the jump function is not implemented for the algorithm specified in the state in the process dictionary.

 Return the seed after performing jump calculation.

Returns the state after performing jump calculation to the given state.

This function generates a not_implemented error exception when the jump function is not implemented for the algorithm specified in the state.

 Return a standard normal distributed random float.

Returns a standard normal deviate float (that is, the mean is 0 and the standard deviation is 1) and updates the state in the process dictionary.

 Return a standard normal distributed random float.

Returns, for a specified state, a standard normal deviate float (that is, the mean is 0 and the standard deviation is 1) and a new state.

 Seed random number generator.

Seeds random number generation with the specifed algorithm and time-dependent data if AlgOrExpState is an algorithm.

Otherwise recreates the exported seed in the process dictionary, and returns the state. See also export_seed/0.

 Seed the random number generation.

Seeds random number generation with the specified algorithm and integers in the process dictionary and returns the state.

 Seed random number generator.

Seeds random number generation with the specifed algorithm and time-dependent data if AlgOrExpState is an algorithm.

Otherwise recreates the exported seed and returns the state. See also export_seed/0.

 Seed the random number generation.

Seeds random number generation with the specified algorithm and integers and returns the state.

 Return a random float.

Returns a random float uniformly distributed in the value range 0.0 < X < 1.0 and updates the state in the process dictionary.

 Return a random integer.

Returns, for a specified integer N >= 1, a random integer uniformly distributed in the value range 1 <= X <= N and updates the state in the process dictionary.

 Return a random float.

Returns, for a specified state, random float uniformly distributed in the value range 0.0 < X < 1.0 and a new state.

 Return a random integer.

Returns, for a specified integer N >= 1 and a state, a random integer uniformly distributed in the value range 1 <= X <= N and a new state.