/usr/lib/swi-prolog/doc/Manual/random.html

<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01//EN" "http://www.w3.org/TR/html4/strict.dtd">

<html>
<head>
<title>SWI-Prolog 7.1.10 Reference Manual: Section A.24</title><link rel="home" href="index.html">
<link rel="contents" href="Contents.html">
<link rel="index" href="DocIndex.html">
<link rel="summary" href="summary.html">
<link rel="previous" href="quasiquotations.html">
<link rel="next" href="readutil.html">

<style type="text/css">

/* Style sheet for SWI-Prolog latex2html
*/

dd.defbody
{ margin-bottom: 1em;
}

dt.pubdef, dt.multidef
{ color: #fff;
padding: 2px 10px 0px 10px;
margin-bottom: 5px;
font-size: 18px;
vertical-align: middle;
overflow: hidden;
}

dt.pubdef { background-color: #0c3d6e; }
dt.multidef { background-color: #ef9439; }

.bib dd
{ margin-bottom: 1em;
}

.bib dt
{ float: left;
margin-right: 1.3ex;
}

pre.code
{ margin-left: 1.5em;
margin-right: 1.5em;
border: 1px dotted;
padding-top: 5px;
padding-left: 5px;
padding-bottom: 5px;
background-color: #f8f8f8;
}

div.navigate
{ text-align: center;
background-color: #f0f0f0;
border: 1px dotted;
padding: 5px;
}

div.title
{ text-align: center;
padding-bottom: 1em;
font-size: 200%;
font-weight: bold;
}

div.author
{ text-align: center;
font-style: italic;
}

div.abstract
{ margin-top: 2em;
background-color: #f0f0f0;
border: 1px dotted;
padding: 5px;
margin-left: 10%; margin-right:10%;
}

div.abstract-title
{ text-align: center;
padding: 5px;
font-size: 120%;
font-weight: bold;
}

div.toc-h1
{ font-size: 200%;
font-weight: bold;
}

div.toc-h2
{ font-size: 120%;
font-weight: bold;
margin-left: 2em;
}

div.toc-h3
{ font-size: 100%;
font-weight: bold;
margin-left: 4em;
}

div.toc-h4
{ font-size: 100%;
margin-left: 6em;
}

span.sec-nr
{
}

span.sec-title
{
}

span.pred-ext
{ font-weight: bold;
}

span.pred-tag
{ float: right;
padding-top: 0.2em;
font-size: 80%;
font-style: italic;
color: #fff;
}

div.caption
{ width: 80%;
margin: auto;
text-align:center;
}

/* Footnotes */
.fn {
color: red;
font-size: 70%;
}

.fn-text, .fnp {
position: absolute;
top: auto;
left: 10%;
border: 1px solid #000;
box-shadow: 5px 5px 5px #888;
display: none;
background: #fff;
color: #000;
margin-top: 25px;
padding: 8px 12px;
font-size: larger;
}

sup:hover span.fn-text
{ display: block;
}

/* Lists */

dl.latex
{ margin-top: 1ex;
margin-bottom: 0.5ex;
}

dl.latex dl.latex dd.defbody
{ margin-bottom: 0.5ex;
}

/* PlDoc Tags */

dl.tags
{ font-size: 90%;
margin-left: 5ex;
margin-top: 1ex;
margin-bottom: 0.5ex;
}

dl.tags dt
{ margin-left: 0pt;
font-weight: bold;
}

dl.tags dd
{ margin-left: 3ex;
}

td.param
{ font-style: italic;
font-weight: bold;
}

/* Index */

dt.index-sep
{ font-weight: bold;
font-size: +1;
margin-top: 1ex;
}

/* Tables */

table.center
{ margin: auto;
}

table.latex
{ border-collapse:collapse;
}

table.latex tr
{ vertical-align: text-top;
}

table.latex td,th
{ padding: 2px 1em;
}

table.latex tr.hline td,th
{ border-top: 1px solid black;
}

table.frame-box
{ border: 2px solid black;
}

</style>
</head>
<body style="background:white">
<div class="navigate"><a class="nav" href="index.html"><img src="home.gif" alt="Home"></a>
<a class="nav" href="Contents.html"><img src="index.gif" alt="Contents"></a>
<a class="nav" href="DocIndex.html"><img src="yellow_pages.gif" alt="Index"></a>
<a class="nav" href="summary.html"><img src="info.gif" alt="Summary"></a>
<a class="nav" href="quasiquotations.html"><img src="prev.gif" alt="Previous"></a>
<a class="nav" href="readutil.html"><img src="next.gif" alt="Next"></a>
</div>
<h2 id="sec:random"><a id="sec:A.24"><span class="sec-nr">A.24</span> <span class="sec-title">library(random): 
Random numbers</span></a></h2>

<p><a id="sec:random"></a>

<dl class="tags">
<dt class="tag">author</dt>
<dd>
R.A. O'Keefe, V.S. Costa, L. Damas, Jan Wielemaker
</dd>
<dt class="tag">See also</dt>
<dd>
Built-in function <a class="pred" href="random.html#random/1">random/1</a>: 
A is <code>random(10)</code>
</dd>
</dl>

<p>This library is derived from the DEC10 library random. Later, the 
core random generator was moved to C. The current version uses the 
SWI-Prolog arithmetic functions to realise this library. These functions 
are based on the GMP library.

<dl class="latex">
<dt class="pubdef"><span class="pred-tag">[det]</span><a id="random/1"><strong>random</strong>(<var>-R:float</var>)</a></dt>
<dd class="defbody">
Binds <var>R</var> to a new random float in the <i>open</i> interval 
(0.0,1.0).

<dl class="tags">
<dt class="mtag">See also</dt>
<dd>
- <a class="pred" href="random.html#setrand/1">setrand/1</a>, <a class="pred" href="random.html#getrand/1">getrand/1</a> 
may be used to fetch/set the state. <br>
- In SWI-Prolog, <a class="pred" href="random.html#random/1">random/1</a> 
is implemented by the function
<span class="pred-ext">random_float/0</span>.
</dd>
</dl>

</dd>
<dt class="pubdef"><span class="pred-tag">[semidet]</span><a id="random_between/3"><strong>random_between</strong>(<var>+L:int, 
+U:int, -R:int</var>)</a></dt>
<dd class="defbody">
Binds <var>R</var> to a random integer in [<var>L</var>,<var>U</var>] 
(i.e., including both <var>L</var> and
<var>U</var>). Fails silently if <var>U</var><var>&lt;</var><var>L</var>.</dd>
<dt class="pubdef"><span class="pred-tag">[det]</span><a id="random/3"><strong>random</strong>(<var>+L:int, 
+U:int, -R:int</var>)</a></dt>
<dt class="pubdef"><span class="pred-tag">[det]</span><a id="random/3"><strong>random</strong>(<var>+L:float, 
+U:float, -R:float</var>)</a></dt>
<dd class="defbody">
Generate a random integer or float in a range. If <var>L</var> and <var>U</var> 
are both integers, <var>R</var> is a random integer in the half open 
interval [<var>L</var>,<var>U</var>). If <var>L</var> and <var>U</var> 
are both floats, <var>R</var> is a float in the open interval (<var>L</var>,<var>U</var>).

<dl class="tags">
<dt class="tag">deprecated</dt>
<dd>
Please use <a class="pred" href="random.html#random/1">random/1</a> for 
generating a random float and <a class="pred" href="random.html#random_between/3">random_between/3</a> 
for generating a random integer. Note that the <a class="pred" href="random.html#random_between/3">random_between/3</a> 
includes the upper bound, while this predicate excludes the upper bound.
</dd>
</dl>

</dd>
<dt class="pubdef"><span class="pred-tag">[det]</span><a id="setrand/1"><strong>setrand</strong>(<var>+State</var>)</a></dt>
<dt class="pubdef"><span class="pred-tag">[det]</span><a id="getrand/1"><strong>getrand</strong>(<var>-State</var>)</a></dt>
<dd class="defbody">
Query/set the state of the random generator. This is intended for 
restarting the generator at a known state only. The predicate <a class="pred" href="random.html#setrand/1">setrand/1</a> 
accepts an opaque term returned by
<a class="pred" href="random.html#getrand/1">getrand/1</a>. This term 
may be asserted, written and read. The application may not make other 
assumptions about this term.

<p>For compatibility reasons with older versions of this library,
<a class="pred" href="random.html#setrand/1">setrand/1</a> also accepts 
a term <code>rand(A,B,C)</code>, where A, B and C are integers in the 
range 1..30,000. This argument is used to seed the random generator. 
Deprecated.

<dl class="tags">
<dt class="tag">Errors</dt>
<dd>
<code>existence_error(random_state, _)</code> is raised if the 
underlying infrastructure cannot fetch the random state. This is 
currently the case if SWI-Prolog is not compiled with the GMP library.
</dd>
<dt class="tag">See also</dt>
<dd>
<a class="pred" href="miscarith.html#set_random/1">set_random/1</a> and <a class="pred" href="miscarith.html#random_property/1">random_property/1</a> 
provide the SWI-Prolog native implementation.
</dd>
</dl>

</dd>
<dt class="pubdef"><span class="pred-tag">[semidet]</span><a id="maybe/0"><strong>maybe</strong></a></dt>
<dd class="defbody">
Succeed/fail with equal probability (variant of <a class="pred" href="random.html#maybe/1">maybe/1</a>).</dd>
<dt class="pubdef"><span class="pred-tag">[semidet]</span><a id="maybe/1"><strong>maybe</strong>(<var>+P</var>)</a></dt>
<dd class="defbody">
Succeed with probability <var>P</var>, fail with probability 1-<var>P</var></dd>
<dt class="pubdef"><span class="pred-tag">[semidet]</span><a id="maybe/2"><strong>maybe</strong>(<var>+K, 
+N</var>)</a></dt>
<dd class="defbody">
Succeed with probability <var>K</var>/<var>N</var> (variant of <a class="pred" href="random.html#maybe/1">maybe/1</a>)</dd>
<dt class="pubdef"><span class="pred-tag">[semidet]</span><a id="random_perm2/4"><strong>random_perm2</strong>(<var>?A, 
?B, ?X, ?Y</var>)</a></dt>
<dd class="defbody">
Does <var>X</var>=<var>A</var>,<var>Y</var>=<var>B</var> or <var>X</var>=<var>B</var>,<var>Y</var>=<var>A</var> 
with equal probability.</dd>
<dt class="pubdef"><span class="pred-tag">[semidet]</span><a id="random_member/2"><strong>random_member</strong>(<var>-X, 
+List:list</var>)</a></dt>
<dd class="defbody">
<var>X</var> is a random member of <var>List</var>. Equivalent to 
random_between(1,
<code>|</code><var>List</var><code>|</code>), followed by <a class="pred" href="lists.html#nth1/3">nth1/3</a>. 
Fails of <var>List</var> is the empty list.

<dl class="tags">
<dt class="tag">Compatibility</dt>
<dd>
Quintus and SICStus libraries.
</dd>
</dl>

</dd>
<dt class="pubdef"><span class="pred-tag">[semidet]</span><a id="random_select/3"><strong>random_select</strong>(<var>-X, 
+List, -Rest</var>)</a></dt>
<dt class="pubdef"><span class="pred-tag">[det]</span><a id="random_select/3"><strong>random_select</strong>(<var>+X, 
-List, +Rest</var>)</a></dt>
<dd class="defbody">
Randomly select or insert an element. Either <var>List</var> or <var>Rest</var> 
must be a list. Fails if <var>List</var> is the empty list.

<dl class="tags">
<dt class="tag">Compatibility</dt>
<dd>
Quintus and SICStus libraries.
</dd>
</dl>

</dd>
<dt class="pubdef"><span class="pred-tag">[det]</span><a id="randset/3"><strong>randset</strong>(<var>+K:int, 
+N:int, -S:list(int)</var>)</a></dt>
<dd class="defbody">
<var>S</var> is a sorted list of <var>K</var> unique random integers in 
the range 1..<var>N</var>. Implemented by enumerating 1..<var>N</var> 
and deciding whether or not the number should be part of the set. For 
example:

<pre class="code">
?- randset(5, 5, S).
S = [1, 2, 3, 4, 5].		(always)
?- randset(5, 20, S).
S = [2, 7, 10, 19, 20].
</pre>

<dl class="tags">
<dt class="tag">See also</dt>
<dd>
<a class="pred" href="random.html#randseq/3">randseq/3</a>.
</dd>
<dt class="tag">bug</dt>
<dd>
Slow if <var>N</var> is large and <var>K</var> is small.
</dd>
</dl>

</dd>
<dt class="pubdef"><span class="pred-tag">[det]</span><a id="randseq/3"><strong>randseq</strong>(<var>+K:int, 
+N:int, -List:list(int)</var>)</a></dt>
<dd class="defbody">
S is a list of <var>K</var> unique random integers in the range 1..<var>N</var>. 
The order is random. Works as if defined by the following code.

<pre class="code">
randseq(K, N, List) :-
      randset(K, N, Set),
      random_permutation(Set, List).
</pre>

<dl class="tags">
<dt class="tag">See also</dt>
<dd>
<a class="pred" href="random.html#randset/3">randset/3</a>.
</dd>
</dl>

</dd>
<dt class="pubdef"><span class="pred-tag">[det]</span><a id="random_permutation/2"><strong>random_permutation</strong>(<var>+List, 
-Permutation</var>)</a></dt>
<dt class="pubdef"><span class="pred-tag">[det]</span><a id="random_permutation/2"><strong>random_permutation</strong>(<var>-List, 
+Permutation</var>)</a></dt>
<dd class="defbody">
<var>Permutation</var> is a random permutation of <var>List</var>. This 
is intended to process the elements of <var>List</var> in random order. 
The predicate is symmetric.

<dl class="tags">
<dt class="tag">Errors</dt>
<dd>
instantiation_error, <code>type_error(list, _)</code>.
</dd>
</dl>

</dd>
</dl>

<p></body></html>
swi-prolog-nox 6.6.4-2ubuntu1 / usr / lib / swi-prolog / doc / Manual / random.html
