random - random number generation.
Please see following description for synopsis
random(3) Erlang Module Definition random(3)
NAME
random - Pseudo-random number generation.
DESCRIPTION
This module provides a random number generator. The method is attrib-
uted 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 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 is 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.
Note:
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.
Note:
The improved rand module is to be used instead of this module.
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(SValue) -> undefined | ran()
Types:
SValue = {A1, A2, A3} | integer()
A1 = A2 = A3 = integer()
seed({A1, A2, A3}) is equivalent to seed(A1, A2, A3).
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.
The following is an easy way of obtaining a unique value to seed
with:
random:seed(erlang:phash2([node()]),
erlang:monotonic_time(),
erlang:unique_integer())
For details, see erlang:phash2/1, erlang:node/0, erlang:mono-
tonic_time/0, and erlang:unique_integer/0.
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
Returns, for a specified integer N >= 1, a random integer uni-
formly distributed between 1 and N, updating the state in the
process dictionary.
uniform_s(State0) -> {float(), State1}
Types:
State0 = State1 = ran()
Returns, for a specified state, a random float uniformly dis-
tributed between 0.0 and 1.0, and a new state.
uniform_s(N, State0) -> {integer(), State1}
Types:
N = integer() >= 1
State0 = State1 = ran()
Returns, for a specified integer N >= 1 and a state, 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 Erlang/OTP R15. Upgrading to R15 breaks
applications that expect a specific output for a specified seed. The
output is still deterministic number series, but different compared to
releases older than R15. Seed {0,0,0} does, for example, no longer pro-
duce a flawed series of only zeros.
Ericsson AB stdlib 3.17 random(3)