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209 lines
15 KiB
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<!-- This manual documents Guile version 3.0.10.
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Copyright (C) 1996-1997, 2000-2005, 2009-2023 Free Software Foundation,
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Inc.
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Copyright (C) 2021 Maxime Devos
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Copyright (C) 2024 Tomas Volf
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Permission is granted to copy, distribute and/or modify this document
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any later version published by the Free Software Foundation; with no
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Invariant Sections, no Front-Cover Texts, and no Back-Cover Texts. A
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copy of the license is included in the section entitled "GNU Free
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Documentation License." -->
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<title>Random (Guile Reference Manual)</title>
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<link href="Concept-Index.html" rel="index" title="Concept Index">
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<link href="index.html#SEC_Contents" rel="contents" title="Table of Contents">
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<link href="Numbers.html" rel="up" title="Numbers">
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<body lang="en">
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<div class="subsubsection-level-extent" id="Random">
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<div class="nav-panel">
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<p>
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Previous: <a href="Bitwise-Operations.html" accesskey="p" rel="prev">Bitwise Operations</a>, Up: <a href="Numbers.html" accesskey="u" rel="up">Numerical data types</a> [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="Concept-Index.html" title="Index" rel="index">Index</a>]</p>
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</div>
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<hr>
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<h4 class="subsubsection" id="Random-Number-Generation"><span>6.6.2.14 Random Number Generation<a class="copiable-link" href="#Random-Number-Generation"> ¶</a></span></h4>
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<p>Pseudo-random numbers are generated from a random state object, which
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can be created with <code class="code">seed->random-state</code> or
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<code class="code">datum->random-state</code>. An external representation (i.e. one
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which can written with <code class="code">write</code> and read with <code class="code">read</code>) of a
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random state object can be obtained via
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<code class="code">random-state->datum</code>. The <var class="var">state</var> parameter to the
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various functions below is optional, it defaults to the state object
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in the <code class="code">*random-state*</code> variable.
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</p>
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<dl class="first-deffn">
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<dt class="deffn" id="index-copy_002drandom_002dstate"><span class="category-def">Scheme Procedure: </span><span><strong class="def-name">copy-random-state</strong> <var class="def-var-arguments">[state]</var><a class="copiable-link" href="#index-copy_002drandom_002dstate"> ¶</a></span></dt>
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<dt class="deffnx def-cmd-deffn" id="index-scm_005fcopy_005frandom_005fstate"><span class="category-def">C Function: </span><span><strong class="def-name">scm_copy_random_state</strong> <var class="def-var-arguments">(state)</var><a class="copiable-link" href="#index-scm_005fcopy_005frandom_005fstate"> ¶</a></span></dt>
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<dd><p>Return a copy of the random state <var class="var">state</var>.
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</p></dd></dl>
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<dl class="first-deffn">
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<dt class="deffn" id="index-random"><span class="category-def">Scheme Procedure: </span><span><strong class="def-name">random</strong> <var class="def-var-arguments">n [state]</var><a class="copiable-link" href="#index-random"> ¶</a></span></dt>
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<dt class="deffnx def-cmd-deffn" id="index-scm_005frandom"><span class="category-def">C Function: </span><span><strong class="def-name">scm_random</strong> <var class="def-var-arguments">(n, state)</var><a class="copiable-link" href="#index-scm_005frandom"> ¶</a></span></dt>
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<dd><p>Return a number in [0, <var class="var">n</var>).
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</p>
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<p>Accepts a positive integer or real n and returns a
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number of the same type between zero (inclusive) and
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<var class="var">n</var> (exclusive). The values returned have a uniform
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distribution.
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</p></dd></dl>
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<dl class="first-deffn">
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<dt class="deffn" id="index-random_003aexp"><span class="category-def">Scheme Procedure: </span><span><strong class="def-name">random:exp</strong> <var class="def-var-arguments">[state]</var><a class="copiable-link" href="#index-random_003aexp"> ¶</a></span></dt>
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<dt class="deffnx def-cmd-deffn" id="index-scm_005frandom_005fexp"><span class="category-def">C Function: </span><span><strong class="def-name">scm_random_exp</strong> <var class="def-var-arguments">(state)</var><a class="copiable-link" href="#index-scm_005frandom_005fexp"> ¶</a></span></dt>
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<dd><p>Return an inexact real in an exponential distribution with mean
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1. For an exponential distribution with mean <var class="var">u</var> use <code class="code">(*
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<var class="var">u</var> (random:exp))</code>.
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</p></dd></dl>
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<dl class="first-deffn">
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<dt class="deffn" id="index-random_003ahollow_002dsphere_0021"><span class="category-def">Scheme Procedure: </span><span><strong class="def-name">random:hollow-sphere!</strong> <var class="def-var-arguments">vect [state]</var><a class="copiable-link" href="#index-random_003ahollow_002dsphere_0021"> ¶</a></span></dt>
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<dt class="deffnx def-cmd-deffn" id="index-scm_005frandom_005fhollow_005fsphere_005fx"><span class="category-def">C Function: </span><span><strong class="def-name">scm_random_hollow_sphere_x</strong> <var class="def-var-arguments">(vect, state)</var><a class="copiable-link" href="#index-scm_005frandom_005fhollow_005fsphere_005fx"> ¶</a></span></dt>
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<dd><p>Fills <var class="var">vect</var> with inexact real random numbers the sum of whose
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squares is equal to 1.0. Thinking of <var class="var">vect</var> as coordinates in
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space of dimension <var class="var">n</var> <em class="math">=</em> <code class="code">(vector-length <var class="var">vect</var>)</code>,
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the coordinates are uniformly distributed over the surface of the unit
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n-sphere.
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</p></dd></dl>
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<dl class="first-deffn">
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<dt class="deffn" id="index-random_003anormal"><span class="category-def">Scheme Procedure: </span><span><strong class="def-name">random:normal</strong> <var class="def-var-arguments">[state]</var><a class="copiable-link" href="#index-random_003anormal"> ¶</a></span></dt>
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<dt class="deffnx def-cmd-deffn" id="index-scm_005frandom_005fnormal"><span class="category-def">C Function: </span><span><strong class="def-name">scm_random_normal</strong> <var class="def-var-arguments">(state)</var><a class="copiable-link" href="#index-scm_005frandom_005fnormal"> ¶</a></span></dt>
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<dd><p>Return an inexact real in a normal distribution. The distribution
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used has mean 0 and standard deviation 1. For a normal distribution
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with mean <var class="var">m</var> and standard deviation <var class="var">d</var> use <code class="code">(+ <var class="var">m</var>
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(* <var class="var">d</var> (random:normal)))</code>.
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</p></dd></dl>
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<dl class="first-deffn">
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<dt class="deffn" id="index-random_003anormal_002dvector_0021"><span class="category-def">Scheme Procedure: </span><span><strong class="def-name">random:normal-vector!</strong> <var class="def-var-arguments">vect [state]</var><a class="copiable-link" href="#index-random_003anormal_002dvector_0021"> ¶</a></span></dt>
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<dt class="deffnx def-cmd-deffn" id="index-scm_005frandom_005fnormal_005fvector_005fx"><span class="category-def">C Function: </span><span><strong class="def-name">scm_random_normal_vector_x</strong> <var class="def-var-arguments">(vect, state)</var><a class="copiable-link" href="#index-scm_005frandom_005fnormal_005fvector_005fx"> ¶</a></span></dt>
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<dd><p>Fills <var class="var">vect</var> with inexact real random numbers that are
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independent and standard normally distributed
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(i.e., with mean 0 and variance 1).
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</p></dd></dl>
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<dl class="first-deffn">
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<dt class="deffn" id="index-random_003asolid_002dsphere_0021"><span class="category-def">Scheme Procedure: </span><span><strong class="def-name">random:solid-sphere!</strong> <var class="def-var-arguments">vect [state]</var><a class="copiable-link" href="#index-random_003asolid_002dsphere_0021"> ¶</a></span></dt>
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<dt class="deffnx def-cmd-deffn" id="index-scm_005frandom_005fsolid_005fsphere_005fx"><span class="category-def">C Function: </span><span><strong class="def-name">scm_random_solid_sphere_x</strong> <var class="def-var-arguments">(vect, state)</var><a class="copiable-link" href="#index-scm_005frandom_005fsolid_005fsphere_005fx"> ¶</a></span></dt>
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<dd><p>Fills <var class="var">vect</var> with inexact real random numbers the sum of whose
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squares is less than 1.0. Thinking of <var class="var">vect</var> as coordinates in
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space of dimension <var class="var">n</var> <em class="math">=</em> <code class="code">(vector-length <var class="var">vect</var>)</code>,
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the coordinates are uniformly distributed within the unit
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<var class="var">n</var>-sphere.
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</p></dd></dl>
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<dl class="first-deffn">
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<dt class="deffn" id="index-random_003auniform"><span class="category-def">Scheme Procedure: </span><span><strong class="def-name">random:uniform</strong> <var class="def-var-arguments">[state]</var><a class="copiable-link" href="#index-random_003auniform"> ¶</a></span></dt>
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<dt class="deffnx def-cmd-deffn" id="index-scm_005frandom_005funiform"><span class="category-def">C Function: </span><span><strong class="def-name">scm_random_uniform</strong> <var class="def-var-arguments">(state)</var><a class="copiable-link" href="#index-scm_005frandom_005funiform"> ¶</a></span></dt>
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<dd><p>Return a uniformly distributed inexact real random number in
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[0,1).
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</p></dd></dl>
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<dl class="first-deffn">
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<dt class="deffn" id="index-seed_002d_003erandom_002dstate"><span class="category-def">Scheme Procedure: </span><span><strong class="def-name">seed->random-state</strong> <var class="def-var-arguments">seed</var><a class="copiable-link" href="#index-seed_002d_003erandom_002dstate"> ¶</a></span></dt>
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<dt class="deffnx def-cmd-deffn" id="index-scm_005fseed_005fto_005frandom_005fstate"><span class="category-def">C Function: </span><span><strong class="def-name">scm_seed_to_random_state</strong> <var class="def-var-arguments">(seed)</var><a class="copiable-link" href="#index-scm_005fseed_005fto_005frandom_005fstate"> ¶</a></span></dt>
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<dd><p>Return a new random state using <var class="var">seed</var>.
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</p></dd></dl>
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<dl class="first-deffn">
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<dt class="deffn" id="index-datum_002d_003erandom_002dstate"><span class="category-def">Scheme Procedure: </span><span><strong class="def-name">datum->random-state</strong> <var class="def-var-arguments">datum</var><a class="copiable-link" href="#index-datum_002d_003erandom_002dstate"> ¶</a></span></dt>
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<dt class="deffnx def-cmd-deffn" id="index-scm_005fdatum_005fto_005frandom_005fstate"><span class="category-def">C Function: </span><span><strong class="def-name">scm_datum_to_random_state</strong> <var class="def-var-arguments">(datum)</var><a class="copiable-link" href="#index-scm_005fdatum_005fto_005frandom_005fstate"> ¶</a></span></dt>
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<dd><p>Return a new random state from <var class="var">datum</var>, which should have been
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obtained by <code class="code">random-state->datum</code>.
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</p></dd></dl>
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<dl class="first-deffn">
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<dt class="deffn" id="index-random_002dstate_002d_003edatum"><span class="category-def">Scheme Procedure: </span><span><strong class="def-name">random-state->datum</strong> <var class="def-var-arguments">state</var><a class="copiable-link" href="#index-random_002dstate_002d_003edatum"> ¶</a></span></dt>
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<dt class="deffnx def-cmd-deffn" id="index-scm_005frandom_005fstate_005fto_005fdatum"><span class="category-def">C Function: </span><span><strong class="def-name">scm_random_state_to_datum</strong> <var class="def-var-arguments">(state)</var><a class="copiable-link" href="#index-scm_005frandom_005fstate_005fto_005fdatum"> ¶</a></span></dt>
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<dd><p>Return a datum representation of <var class="var">state</var> that may be written out and
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read back with the Scheme reader.
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</p></dd></dl>
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<dl class="first-deffn">
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<dt class="deffn" id="index-random_002dstate_002dfrom_002dplatform"><span class="category-def">Scheme Procedure: </span><span><strong class="def-name">random-state-from-platform</strong><a class="copiable-link" href="#index-random_002dstate_002dfrom_002dplatform"> ¶</a></span></dt>
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<dt class="deffnx def-cmd-deffn" id="index-scm_005frandom_005fstate_005ffrom_005fplatform"><span class="category-def">C Function: </span><span><strong class="def-name">scm_random_state_from_platform</strong> <var class="def-var-arguments">()</var><a class="copiable-link" href="#index-scm_005frandom_005fstate_005ffrom_005fplatform"> ¶</a></span></dt>
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<dd><p>Construct a new random state seeded from a platform-specific source of
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entropy, appropriate for use in non-security-critical applications.
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Currently <samp class="file">/dev/urandom</samp> is tried first, or else the seed is based
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on the time, date, process ID, an address from a freshly allocated heap
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cell, an address from the local stack frame, and a high-resolution timer
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if available.
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</p></dd></dl>
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<dl class="first-defvr first-defvar-alias-first-defvr">
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<dt class="defvr defvar-alias-defvr" id="index-_002arandom_002dstate_002a"><span class="category-def">Variable: </span><span><strong class="def-name">*random-state*</strong><a class="copiable-link" href="#index-_002arandom_002dstate_002a"> ¶</a></span></dt>
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<dd><p>The global random state used by the above functions when the
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<var class="var">state</var> parameter is not given.
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</p></dd></dl>
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<p>Note that the initial value of <code class="code">*random-state*</code> is the same every
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time Guile starts up. Therefore, if you don’t pass a <var class="var">state</var>
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parameter to the above procedures, and you don’t set
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<code class="code">*random-state*</code> to <code class="code">(seed->random-state your-seed)</code>, where
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<code class="code">your-seed</code> is something that <em class="emph">isn’t</em> the same every time,
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you’ll get the same sequence of “random” numbers on every run.
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</p>
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<p>For example, unless the relevant source code has changed, <code class="code">(map
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random (cdr (iota 30)))</code>, if the first use of random numbers since
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Guile started up, will always give:
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</p>
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<div class="example lisp">
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<pre class="lisp-preformatted">(map random (cdr (iota 19)))
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⇒
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(0 1 1 2 2 2 1 2 6 7 10 0 5 3 12 5 5 12)
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</pre></div>
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<p>To seed the random state in a sensible way for non-security-critical
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applications, do this during initialization of your program:
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</p>
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<div class="example lisp">
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<pre class="lisp-preformatted">(set! *random-state* (random-state-from-platform))
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</pre></div>
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</div>
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<hr>
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<div class="nav-panel">
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<p>
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Previous: <a href="Bitwise-Operations.html">Bitwise Operations</a>, Up: <a href="Numbers.html">Numerical data types</a> [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="Concept-Index.html" title="Index" rel="index">Index</a>]</p>
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</div>
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</body>
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</html>
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