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At Brian Wichmann's request, added words warning against 

using the old Wichmann-Hill generator,  Also pointed to
a newer version of his generator, and weakened the claim
about what jumpahead() does now.

Note sure I got the LaTeX entirely correct for \seeurl.
If it's broken, please fix it ;-)

Bugfix candidate!  (These changes make just as much
sense for 2.4.)
This commit is contained in:
Tim Peters 2006-02-21 19:19:00 +00:00
parent b075fcea3a
commit d34350e47e
1 changed files with 13 additions and 4 deletions
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17
Doc/lib/librandom.tex
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@ -34,7 +34,7 @@ hidden instance of the \class{random.Random} class. You can
instantiate your own instances of \class{Random} to get generators instantiate your own instances of \class{Random} to get generators
that don't share state. This is especially useful for multi-threaded that don't share state. This is especially useful for multi-threaded
programs, creating a different instance of \class{Random} for each 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. generated sequences seen by each thread don't overlap.
Class \class{Random} can also be subclassed if you want to use a 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} \versionadded[the \method{getrandombits()} method]{2.4}
As an example of subclassing, the \module{random} module provides 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 in pure Python. The class provides a backward compatible way to
reproduce results from earlier versions of Python which used the reproduce results from earlier versions of Python, which used the
Wichmann-Hill algorithm as the core generator. 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} \versionchanged[Substituted MersenneTwister for Wichmann-Hill]{2.3}
@ -273,4 +277,9 @@ called.
\seetext{Wichmann, B. A. \& Hill, I. D., ``Algorithm AS 183: \seetext{Wichmann, B. A. \& Hill, I. D., ``Algorithm AS 183:
An efficient and portable pseudo-random number generator'', An efficient and portable pseudo-random number generator'',
\citetitle{Applied Statistics} 31 (1982) 188-190.} \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} \end{seealso}