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+<?xml version="1.0" encoding="utf-8" ?>
+<!DOCTYPE erlref SYSTEM "erlref.dtd">
+
+<erlref>
+ <header>
+ <copyright>
+ <year>2015</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>rand</title>
+ <prepared></prepared>
+ <responsible></responsible>
+ <docno>1</docno>
+ <approved></approved>
+ <checked></checked>
+ <date></date>
+ <rev>A</rev>
+ <file>rand.xml</file>
+ </header>
+ <module>rand</module>
+ <modulesummary>Pseudo random number generation</modulesummary>
+ <description>
+ <p>Random number generator.</p>
+
+ <p>The module contains several different algorithms and can be
+ extended with more in the future. The current uniform
+ distribution algorithms uses the
+ <url href="http://xorshift.di.unimi.it">
+ scrambled Xorshift algorithms by Sebastiano Vigna</url> and the
+ normal distribution algorithm uses the
+ <url href="http://www.jstatsoft.org/v05/i08">
+ Ziggurat Method by Marsaglia and Tsang</url>.
+ </p>
+
+ <p>The implemented algorithms are:</p>
+ <taglist>
+ <tag><c>exsplus</c></tag> <item>Xorshift116+, 58 bits precision and period of 2^116-1.</item>
+ <tag><c>exs64</c></tag> <item>Xorshift64*, 64 bits precision and a period of 2^64-1.</item>
+ <tag><c>exs1024</c></tag> <item>Xorshift1024*, 64 bits precision and a period of 2^1024-1.</item>
+ </taglist>
+
+ <p>The current default algorithm is <c>exsplus</c>. The default
+ may change in future. If a specific algorithm is required make
+ sure to always use <seealso marker="#seed-1">seed/1</seealso>
+ to initialize the state.
+ </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 or it can be an explicit argument and return value.
+ </p>
+
+ <p>The functions with implicit state use the process dictionary
+ variable <c>rand_seed</c> to remember the current state.</p>
+
+ <p>If a process calls <seealso marker="#uniform-0">uniform/0</seealso> or
+ <seealso marker="#uniform-1">uniform/1</seealso> without
+ setting a seed first, <seealso marker="#seed-1">seed/1</seealso>
+ is called automatically with the default algorithm and creates a
+ non-constant seed.</p>
+
+ <p>The functions with explicit state never use the process
+ dictionary.</p>
+
+ <p>Examples:</p>
+ <pre>
+ %% Simple usage. Creates and seeds the default algorithm
+ %% with a non-constant seed if not already done.
+ R0 = rand:uniform(),
+ R1 = rand:uniform(),
+
+ %% Use a given algorithm.
+ _ = rand:seed(exs1024),
+ R2 = rand:uniform(),
+
+ %% Use a given algorithm with a constant seed.
+ _ = rand:seed(exs1024, {123, 123534, 345345}),
+ R3 = rand:uniform(),
+
+ %% Use the functional api with non-constant seed.
+ S0 = rand:seed_s(exsplus),
+ {R4, S1} = rand:uniform_s(S0),
+
+ %% Create a standard normal deviate.
+ {SND0, S2} = rand:normal_s(S1),
+ </pre>
+
+ <note><p>This random number generator is not cryptographically
+ strong. If a strong cryptographic random number generator is
+ needed, use one of functions in the
+ <seealso marker="crypto:crypto">crypto</seealso>
+ module, for example <c>crypto:rand_bytes/1</c>.</p></note>
+ </description>
+ <datatypes>
+ <datatype>
+ <name name="alg"/>
+ </datatype>
+
+ <datatype>
+ <name name="state"/>
+ <desc><p>Algorithm dependent state.</p></desc>
+ </datatype>
+
+ <datatype>
+ <name name="export_state"/>
+ <desc><p>Algorithm dependent state which can be printed or saved to file.</p></desc>
+ </datatype>
+ </datatypes>
+
+ <funcs>
+ <func>
+ <name name="seed" arity="1"/>
+ <fsummary>Seed random number generator</fsummary>
+ <desc>
+ <marker id="seed-1"/>
+ <p>Seeds random number generation with the given algorithm and time dependent
+ data if <anno>AlgOrExpState</anno> is an algorithm.</p>
+ <p>Otherwise recreates the exported seed in the process
+ dictionary, and returns the state.
+ <em>See also:</em> <seealso marker="#export_seed-0">export_seed/0</seealso>.</p>
+ </desc>
+ </func>
+ <func>
+ <name name="seed_s" arity="1"/>
+ <fsummary>Seed random number generator</fsummary>
+ <desc>
+ <p>Seeds random number generation with the given algorithm and time dependent
+ data if <anno>AlgOrExpState</anno> is an algorithm.</p>
+ <p>Otherwise recreates the exported seed and returns the state.
+ <em>See also:</em> <seealso marker="#export_seed-0">export_seed/0</seealso>.</p>
+ </desc>
+ </func>
+ <func>
+ <name name="seed" arity="2"/>
+ <fsummary>Seed the random number generation</fsummary>
+ <desc>
+ <p>Seeds random number generation with the given algorithm and
+ integers in the process dictionary and returns
+ the state.</p>
+ </desc>
+ </func>
+ <func>
+ <name name="seed_s" arity="2"/>
+ <fsummary>Seed the random number generation</fsummary>
+ <desc>
+ <p>Seeds random number generation with the given algorithm and
+ integers and returns the state.</p>
+ </desc>
+ </func>
+
+ <func>
+ <name name="export_seed" arity="0"/>
+ <fsummary>Export the random number generation state</fsummary>
+ <desc><marker id="export_seed-0"/>
+ <p>Returns the random number state in an external format.
+ To be used with <seealso marker="#seed-1">seed/1</seealso>.</p>
+ </desc>
+ </func>
+
+ <func>
+ <name name="export_seed_s" arity="1"/>
+ <fsummary>Export the random number generation state</fsummary>
+ <desc><marker id="export_seed_s-1"/>
+ <p>Returns the random number generator state in an external format.
+ To be used with <seealso marker="#seed-1">seed/1</seealso>.</p>
+ </desc>
+ </func>
+
+ <func>
+ <name name="uniform" arity="0"/>
+ <fsummary>Return a random float</fsummary>
+ <desc>
+ <marker id="uniform-0"/>
+ <p>Returns a random float uniformly distributed in the value
+ range <c>0.0 &lt; <anno>X</anno> &lt; 1.0 </c> and
+ updates the state in the process dictionary.</p>
+ </desc>
+ </func>
+ <func>
+ <name name="uniform_s" arity="1"/>
+ <fsummary>Return a random float</fsummary>
+ <desc>
+ <p>Given a state, <c>uniform_s/1</c> returns a random float
+ uniformly distributed in the value range <c>0.0 &lt;
+ <anno>X</anno> &lt; 1.0</c> and a new state.</p>
+ </desc>
+ </func>
+
+ <func>
+ <name name="uniform" arity="1"/>
+ <fsummary>Return a random integer</fsummary>
+ <desc>
+ <marker id="uniform-1"/>
+ <p>Given an integer <c><anno>N</anno> >= 1</c>,
+ <c>uniform/1</c> returns a random integer uniformly
+ distributed in the value range
+ <c>1 &lt;= <anno>X</anno> &lt;= <anno>N</anno></c> and
+ updates the state in the process dictionary.</p>
+ </desc>
+ </func>
+ <func>
+ <name name="uniform_s" arity="2"/>
+ <fsummary>Return a random integer</fsummary>
+ <desc>
+ <p>Given an integer <c><anno>N</anno> >= 1</c> and a state,
+ <c>uniform_s/2</c> returns a random integer uniformly
+ distributed in the value range <c>1 &lt;= <anno>X</anno> &lt;=
+ <anno>N</anno></c> and a new state.</p>
+ </desc>
+ </func>
+
+ <func>
+ <name name="normal" arity="0"/>
+ <fsummary>Return a standard normal distributed random float</fsummary>
+ <desc>
+ <p>Returns a standard normal deviate float (that is, the mean
+ is 0 and the standard deviation is 1) and updates the state in
+ the process dictionary.</p>
+ </desc>
+ </func>
+ <func>
+ <name name="normal_s" arity="1"/>
+ <fsummary>Return a standard normal distributed random float</fsummary>
+ <desc>
+ <p>Given a state, <c>normal_s/1</c> returns a standard normal
+ deviate float (that is, the mean is 0 and the standard
+ deviation is 1) and a new state.</p>
+ </desc>
+ </func>
+
+ </funcs>
+</erlref>