Doc/lib/libwhrandom.tex

   1 \section{\module{whrandom} ---
   2          Pseudo-random number generator}
   3
   4 \declaremodule{standard}{whrandom}
   5 \modulesynopsis{Floating point pseudo-random number generator.}
   6
   7
   8 This module implements a Wichmann-Hill pseudo-random number generator
   9 class that is also named \class{whrandom}.  Instances of the
  10 \class{whrandom} class conform to the Random Number Generator
  11 interface described in section \ref{rng-objects}.  They also offer the
  12 following method, specific to the Wichmann-Hill algorithm:
  13
  14 \begin{methoddesc}[whrandom]{seed}{\optional{x, y, z}}
  15   Initializes the random number generator from the integers \var{x},
  16   \var{y} and \var{z}.  When the module is first imported, the random
  17   number is initialized using values derived from the current time.
  18   If \var{x}, \var{y}, and \var{z} are either omitted or \code{0}, the
  19   seed will be computed from the current system time.  If one or two
  20   of the parameters are \code{0}, but not all three, the zero values
  21   are replaced by ones.  This causes some apparently different seeds
  22   to be equal, with the corresponding result on the pseudo-random
  23   series produced by the generator.
  24 \end{methoddesc}
  25
  26 \begin{funcdesc}{choice}{seq}
  27 Chooses a random element from the non-empty sequence \var{seq} and returns it.
  28 \end{funcdesc}
  29
  30 \begin{funcdesc}{randint}{a, b}
  31 Returns a random integer \var{N} such that \code{\var{a}<=\var{N}<=\var{b}}.
  32 \end{funcdesc}
  33
  34 \begin{funcdesc}{random}{}
  35 Returns the next random floating point number in the range [0.0 ... 1.0).
  36 \end{funcdesc}
  37
  38 \begin{funcdesc}{seed}{x, y, z}
  39 Initializes the random number generator from the integers \var{x},
  40 \var{y} and \var{z}.  When the module is first imported, the random
  41 number is initialized using values derived from the current time.
  42 \end{funcdesc}
  43
  44 \begin{funcdesc}{uniform}{a, b}
  45 Returns a random real number \var{N} such that \code{\var{a}<=\var{N}<\var{b}}.
  46 \end{funcdesc}
  47
  48 When imported, the \module{whrandom} module also creates an instance of
  49 the \class{whrandom} class, and makes the methods of that instance
  50 available at the module level.  Therefore one can write either
  51 \code{N = whrandom.random()} or:
  52
  53 \begin{verbatim}
  54 generator = whrandom.whrandom()
  55 N = generator.random()
  56 \end{verbatim}
  57
  58 Note that using separate instances of the generator leads to
  59 independent sequences of pseudo-random numbers.
  60
  61 \begin{seealso}
  62   \seemodule{random}{Generators for various random distributions and
  63                      documentation for the Random Number Generator
  64                      interface.}
  65   \seetext{Wichmann, B. A. \& Hill, I. D., ``Algorithm AS 183:
  66            An efficient and portable pseudo-random number generator'',
  67            \citetitle{Applied Statistics} 31 (1982) 188-190.}
  68 \end{seealso}