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diff --git a/lib/stdlib/doc/src/rand.xml b/lib/stdlib/doc/src/rand.xml new file mode 100644 index 0000000000..178afda5a0 --- /dev/null +++ b/lib/stdlib/doc/src/rand.xml @@ -0,0 +1,246 @@ +<?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 < <anno>X</anno> < 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 < + <anno>X</anno> < 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 <= <anno>X</anno> <= <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 <= <anno>X</anno> <= + <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> |