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<H1>random</H1>
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<H3>MODULE</H3>
<DIV CLASS=REFBODY>
random
</DIV>
<H3>MODULE SUMMARY</H3>
<DIV CLASS=REFBODY>
Pseudo random number generation
</DIV>
<H3>DESCRIPTION</H3>
<DIV CLASS=REFBODY>
<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>The current algorithm is a modification of the version attributed
to Richard A O'Keefe in the standard Prolog library.
<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 <CODE>ran()</CODE>) consists of a
tuple of three integers.
</DIV>
<H3>EXPORTS</H3>
<P><A NAME="seed/0"><STRONG><CODE>seed() -> ran()</CODE></STRONG></A><BR>
<DIV CLASS=REFBODY>
<P>Seeds random number generation with default (fixed) values
in the process dictionary, and returns the old state.
</DIV>
<P><A NAME="seed/3"><STRONG><CODE>seed(A1, A2, A3) -> ran()</CODE></STRONG></A><BR>
<DIV CLASS=REFBODY><P>Types:
<DIV CLASS=REFTYPES>
<P>
<STRONG><CODE>A1 = A2 = A3 = int()</CODE></STRONG><BR>
</DIV>
</DIV>
<DIV CLASS=REFBODY>
<P>Seeds random number generation with integer values in the process
dictionary, and returns the old state.
</DIV>
<P><A NAME="seed0/0"><STRONG><CODE>seed0() -> ran()</CODE></STRONG></A><BR>
<DIV CLASS=REFBODY>
<P>Returns the default state.
</DIV>
<P><A NAME="uniform/0"><STRONG><CODE>uniform()-> float()</CODE></STRONG></A><BR>
<DIV CLASS=REFBODY>
<P>Returns a random float uniformly distributed between <CODE>0.0</CODE>
and <CODE>1.0</CODE>, updating the state in the process dictionary.
</DIV>
<P><A NAME="uniform/1"><STRONG><CODE>uniform(N) -> int()</CODE></STRONG></A><BR>
<DIV CLASS=REFBODY><P>Types:
<DIV CLASS=REFTYPES>
<P>
<STRONG><CODE>N = int()</CODE></STRONG><BR>
</DIV>
</DIV>
<DIV CLASS=REFBODY>
<P>Given an integer <CODE>N >= 1</CODE>, <CODE>uniform/1</CODE> returns a
random integer uniformly distributed between <CODE>1</CODE> and
<CODE>N</CODE>, updating the state in the process dictionary.
</DIV>
<P><A NAME="uniform_s/1"><STRONG><CODE>uniform_s(State0) -> {float(), State1}</CODE></STRONG></A><BR>
<DIV CLASS=REFBODY><P>Types:
<DIV CLASS=REFTYPES>
<P>
<STRONG><CODE>State0 = State1 = ran()</CODE></STRONG><BR>
</DIV>
</DIV>
<DIV CLASS=REFBODY>
<P>Given a state, <CODE>uniform_s/1</CODE>returns a random float uniformly
distributed between <CODE>0.0</CODE> and <CODE>1.0</CODE>, and a new state.
</DIV>
<P><A NAME="uniform_s/2"><STRONG><CODE>uniform_s(N, State0) -> {int(), State1}</CODE></STRONG></A><BR>
<DIV CLASS=REFBODY><P>Types:
<DIV CLASS=REFTYPES>
<P>
<STRONG><CODE>N = int()</CODE></STRONG><BR>
<STRONG><CODE>State0 = State1 = ran()</CODE></STRONG><BR>
</DIV>
</DIV>
<DIV CLASS=REFBODY>
<P>Given an integer <CODE>N >= 1</CODE> and a state, <CODE>uniform_s/2</CODE>
returns a random integer uniformly distributed between <CODE>1</CODE> and
<CODE>N</CODE>, and a new state.
</DIV>
<H3>Note</H3>
<DIV CLASS=REFBODY>
<P>Some of the functions use the process dictionary variable
<CODE>random_seed</CODE> to remember the current seed.
<P> If a process calls <CODE>uniform/0</CODE> or <CODE>uniform/1</CODE> without
setting a seed first, <CODE>seed/0</CODE> is called automatically.
</DIV>
<H3>AUTHORS</H3>
<DIV CLASS=REFBODY>
Joe Armstrong - support@erlang.ericsson.se<BR>
</DIV>
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<HR>
<SMALL>stdlib 1.14.2<BR>
Copyright © 1991-2006
<A HREF="http://www.erlang.se">Ericsson AB</A><BR>
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