# random

### MODULE

random

### MODULE SUMMARY

Pseudo random number generation

### DESCRIPTION

Random number generator. The method is attributed to B.A. Wichmann and I.D.Hill, in 'An efficient and portable pseudo-random number generator', Journal of Applied Statistics. AS183. 1982. Also Byte March 1987.

The current algorithm is a modification of the version attributed to Richard A O'Keefe in the standard Prolog library.

Every time a random number is requested, a state is used to calculate it, and a new state produced. The state can either be implicit (kept in the process dictionary) or be an explicit argument and return value. In this implementation, the state (the type `ran()`) consists of a tuple of three integers.

### EXPORTS

`seed() -> ran()`

Seeds random number generation with default (fixed) values in the process dictionary, and returns the old state.

`seed(A1, A2, A3) -> ran()`

Types:

`A1 = A2 = A3 = int()`

Seeds random number generation with integer values in the process dictionary, and returns the old state.

`seed0() -> ran()`

Returns the default state.

`uniform()-> float()`

Returns a random float uniformly distributed between `0.0` and `1.0`, updating the state in the process dictionary.

`uniform(N) -> int()`

Types:

`N = int()`

Given an integer `N >= 1`, `uniform/1` returns a random integer uniformly distributed between `1` and `N`, updating the state in the process dictionary.

`uniform_s(State0) -> {float(), State1}`

Types:

`State0 = State1 = ran()`

Given a state, `uniform_s/1`returns a random float uniformly distributed between `0.0` and `1.0`, and a new state.

`uniform_s(N, State0) -> {int(), State1}`

Types:

`N = int()`
`State0 = State1 = ran()`

Given an integer `N >= 1` and a state, `uniform_s/2` returns a random integer uniformly distributed between `1` and `N`, and a new state.

### Note

Some of the functions use the process dictionary variable `random_seed` to remember the current seed.

If a process calls `uniform/0` or `uniform/1` without setting a seed first, `seed/0` is called automatically.

### AUTHORS

Joe Armstrong - support@erlang.ericsson.se

stdlib 1.12
Copyright © 1991-2003 Ericsson Utvecklings AB