random

19962016 Ericsson AB. All Rights Reserved. Licensed under the Apache License, Version 2.0 (the "License"); you may not use this file except in compliance with the License. You may obtain a copy of the License at http://www.apache.org/licenses/LICENSE-2.0 Unless required by applicable law or agreed to in writing, software distributed under the License is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the License for the specific language governing permissions and limitations under the License. random Joe Armstrong Bjarne Däcker 1 Bjarne Däcker 1996-09-09 A random.xml

random Pseudo-random number generation.

This module provides a 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 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.

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.

The improved rand module is to be used instead of this module.

The state.

Seed random number generation with default values.

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

Seed random number generator.

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

Seed random number generator.

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:monotonic_time/0, and erlang:unique_integer/0.

Return default state for random number generation.

Returns the default state.

Return a random float.

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

Return a random integer.

Returns, for a specified integer N >= 1, a random integer uniformly distributed between 1 and N, updating the state in the process dictionary.

Return a random float.

Returns, for a specified state, a random float uniformly distributed between 0.0 and 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 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 produce a flawed series of only zeros.