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random(3erl) | Erlang Module Definition | random(3erl) |

# NAME¶

random - 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. It should be noted that this random number generator is not cryptographically strong. If a strong cryptographic random number generator is needed for example

*crypto:rand_bytes/1*could be used instead.

# DATA TYPES¶

ran()= {integer(), integer(), integer()}

The state.

# EXPORTS¶

seed() -> ran()

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

seed(A1, A2, A3) -> undefined | ran()

Types:

A1 = A2 = A3 = integer()

Seeds random number generation with integer values in the process dictionary,
and returns the old state.
One way of obtaining a seed is to use the BIF

*now/0*:... {A1,A2,A3} = now(), random:seed(A1, A2, A3), ...

seed(X1 :: {A1, A2, A3}) -> undefined | ran()

Types:

A1 = A2 = A3 = integer()

*seed({A1, A2, A3})*is equivalent to

*seed(A1, A2, A3)*.

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) -> integer() >= 1

Types:

N = integer() >= 1

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) -> {integer(), State1}

Types:

N = integer() >= 1
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. The implementation changed in R15. Upgrading to R15 will break applications that expect a specific output for a given seed. The output is still deterministic number series, but different compared to releases older than R15. The seed

*{0,0,0}*will for example no longer produce a flawed series of only zeros.

stdlib 2.2 | Ericsson AB |