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| -rw-r--r-- | Doc/lib/librandom.tex | 17 |
1 files changed, 13 insertions, 4 deletions
diff --git a/Doc/lib/librandom.tex b/Doc/lib/librandom.tex index f95f106..7a1b982 100644 --- a/Doc/lib/librandom.tex +++ b/Doc/lib/librandom.tex @@ -34,7 +34,7 @@ hidden instance of the \class{random.Random} class. You can instantiate your own instances of \class{Random} to get generators that don't share state. This is especially useful for multi-threaded programs, creating a different instance of \class{Random} for each -thread, and using the \method{jumpahead()} method to ensure that the +thread, and using the \method{jumpahead()} method to make it likely that the generated sequences seen by each thread don't overlap. Class \class{Random} can also be subclassed if you want to use a @@ -47,10 +47,14 @@ over an arbitrarily large range. \versionadded[the \method{getrandombits()} method]{2.4} As an example of subclassing, the \module{random} module provides -the \class{WichmannHill} class which implements an alternative generator +the \class{WichmannHill} class that implements an alternative generator in pure Python. The class provides a backward compatible way to -reproduce results from earlier versions of Python which used the -Wichmann-Hill algorithm as the core generator. +reproduce results from earlier versions of Python, which used the +Wichmann-Hill algorithm as the core generator. Note that this Wichmann-Hill +generator can no longer be recommended: its period is too short by +contemporary standards, and the sequence generated is known to fail some +stringent randomness tests. See the references below for a recent +variant that repairs these flaws. \versionchanged[Substituted MersenneTwister for Wichmann-Hill]{2.3} @@ -273,4 +277,9 @@ called. \seetext{Wichmann, B. A. \& Hill, I. D., ``Algorithm AS 183: An efficient and portable pseudo-random number generator'', \citetitle{Applied Statistics} 31 (1982) 188-190.} + + \seeurl{http://www.npl.co.uk/ssfm/download/abstracts.html#196}{A modern + variation of the Wichmann-Hill generator that greatly increases + the period, and passes now-standard statistical tests that the + original generator failed.} \end{seealso} |