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authorErlang/OTP <[email protected]>2009-11-20 14:54:40 +0000
committerErlang/OTP <[email protected]>2009-11-20 14:54:40 +0000
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The R13B03 release.OTP_R13B03
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+<?xml version="1.0" encoding="latin1" ?>
+<!DOCTYPE erlref SYSTEM "erlref.dtd">
+
+<erlref>
+ <header>
+ <copyright>
+ <year>1996</year><year>2009</year>
+ <holder>Ericsson AB. All Rights Reserved.</holder>
+ </copyright>
+ <legalnotice>
+ The contents of this file are subject to the Erlang Public License,
+ Version 1.1, (the "License"); you may not use this file except in
+ compliance with the License. You should have received a copy of the
+ Erlang Public License along with this software. If not, it can be
+ retrieved online at http://www.erlang.org/.
+
+ Software distributed under the License is distributed on an "AS IS"
+ basis, WITHOUT WARRANTY OF ANY KIND, either express or implied. See
+ the License for the specific language governing rights and limitations
+ under the License.
+
+ </legalnotice>
+
+ <title>random</title>
+ <prepared>Joe Armstrong</prepared>
+ <responsible>Bjarne Dacker</responsible>
+ <docno>1</docno>
+ <approved>Bjarne D&auml;cker</approved>
+ <checked></checked>
+ <date>96-09-09</date>
+ <rev>A</rev>
+ <file>random.sgml</file>
+ </header>
+ <module>random</module>
+ <modulesummary>Pseudo random number generation</modulesummary>
+ <description>
+ <p>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. </p>
+ <p>The current algorithm is a modification of the version attributed
+ to Richard A O'Keefe in the standard Prolog library.</p>
+ <p>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 <c>ran()</c>) consists of a
+ tuple of three integers.</p>
+ <p>It should be noted that this random number generator is not cryptographically
+ strong. If a strong cryptographic random number generator is needed for
+ example <c>crypto:rand_bytes/1</c> could be used instead.</p>
+ </description>
+ <funcs>
+ <func>
+ <name>seed() -> ran()</name>
+ <fsummary>Seeds random number generation with default values</fsummary>
+ <desc>
+ <p>Seeds random number generation with default (fixed) values
+ in the process dictionary, and returns the old state.</p>
+ </desc>
+ </func>
+ <func>
+ <name>seed(A1, A2, A3) -> undefined | ran()</name>
+ <fsummary>Seeds random number generator</fsummary>
+ <type>
+ <v>A1 = A2 = A3 = integer()</v>
+ </type>
+ <desc>
+ <p>Seeds random number generation with integer values in the process
+ dictionary, and returns the old state.</p>
+ <p>One way of obtaining a seed is to use the BIF <c>now/0</c>:</p>
+ <code type="none">
+ ...
+ {A1,A2,A3} = now(),
+ random:seed(A1, A2, A3),
+ ...</code>
+ </desc>
+ </func>
+ <func>
+ <name>seed({A1, A2, A3}) -> undefined | ran()</name>
+ <fsummary>Seeds random number generator</fsummary>
+ <type>
+ <v>A1 = A2 = A3 = integer()</v>
+ </type>
+ <desc>
+ <p>
+ <c>seed({A1, A2, A3})</c> is equivalent to <c>seed(A1, A2, A3)</c>.
+ </p>
+ </desc>
+ </func>
+ <func>
+ <name>seed0() -> ran()</name>
+ <fsummary>Return default state for random number generation</fsummary>
+ <desc>
+ <p>Returns the default state.</p>
+ </desc>
+ </func>
+ <func>
+ <name>uniform()-> float()</name>
+ <fsummary>Return a random float</fsummary>
+ <desc>
+ <p>Returns a random float uniformly distributed between <c>0.0</c>
+ and <c>1.0</c>, updating the state in the process dictionary.</p>
+ </desc>
+ </func>
+ <func>
+ <name>uniform(N) -> integer()</name>
+ <fsummary>Return a random integer</fsummary>
+ <type>
+ <v>N = integer()</v>
+ </type>
+ <desc>
+ <p>Given an integer <c>N >= 1</c>, <c>uniform/1</c> returns a
+ random integer uniformly distributed between <c>1</c> and
+ <c>N</c>, updating the state in the process dictionary.</p>
+ </desc>
+ </func>
+ <func>
+ <name>uniform_s(State0) -> {float(), State1}</name>
+ <fsummary>Return a random float</fsummary>
+ <type>
+ <v>State0 = State1 = ran()</v>
+ </type>
+ <desc>
+ <p>Given a state, <c>uniform_s/1</c>returns a random float uniformly
+ distributed between <c>0.0</c> and <c>1.0</c>, and a new state.</p>
+ </desc>
+ </func>
+ <func>
+ <name>uniform_s(N, State0) -> {integer(), State1}</name>
+ <fsummary>Return a random integer</fsummary>
+ <type>
+ <v>N = integer()</v>
+ <v>State0 = State1 = ran()</v>
+ </type>
+ <desc>
+ <p>Given an integer <c>N >= 1</c> and a state, <c>uniform_s/2</c>
+ returns a random integer uniformly distributed between <c>1</c> and
+ <c>N</c>, and a new state.</p>
+ </desc>
+ </func>
+ </funcs>
+
+ <section>
+ <title>Note</title>
+ <p>Some of the functions use the process dictionary variable
+ <c>random_seed</c> to remember the current seed.</p>
+ <p>If a process calls <c>uniform/0</c> or <c>uniform/1</c> without
+ setting a seed first, <c>seed/0</c> is called automatically.</p>
+ </section>
+</erlref>
+