
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 pseudorandom 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.
EXPORTS
seed() > ran()
Seeds random number generation with default (fixed) values in the process dictio
nary, 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({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()
Types N = integer()
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()
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 cur
rent seed.
If a process calls uniform/0 or uniform/1 without setting a seed first, seed/0 is called
automatically.
Ericsson AB stdlib 1.17.3 random(3erl) 
