FAQ 4.10 Why aren't my random numbers random?
- From: PerlFAQ Server <comdog@xxxxxxxxx>
- Date: Fri, 6 May 2005 22:03:01 +0000 (UTC)
This message is one of several periodic postings to comp.lang.perl.misc
intended to make it easier for perl programmers to find answers to
common questions. The core of this message represents an excerpt
from the documentation provided with Perl.
--------------------------------------------------------------------
4.10: Why aren't my random numbers random?
If you're using a version of Perl before 5.004, you must call "srand"
once at the start of your program to seed the random number generator.
BEGIN { srand() if $] < 5.004 }
5.004 and later automatically call "srand" at the beginning. Don't call
"srand" more than once---you make your numbers less random, rather than
more.
Computers are good at being predictable and bad at being random (despite
appearances caused by bugs in your programs :-). see the random article
in the "Far More Than You Ever Wanted To Know" collection in
http://www.cpan.org/misc/olddoc/FMTEYEWTK.tgz , courtesy of Tom Phoenix,
talks more about this. John von Neumann said, ``Anyone who attempts to
generate random numbers by deterministic means is, of course, living in
a state of sin.''
If you want numbers that are more random than "rand" with "srand"
provides, you should also check out the Math::TrulyRandom module from
CPAN. It uses the imperfections in your system's timer to generate
random numbers, but this takes quite a while. If you want a better
pseudorandom generator than comes with your operating system, look at
``Numerical Recipes in C'' at http://www.nr.com/ .
--------------------------------------------------------------------
Documents such as this have been called "Answers to Frequently
Asked Questions" or FAQ for short. They represent an important
part of the Usenet tradition. They serve to reduce the volume of
redundant traffic on a news group by providing quality answers to
questions that keep coming up.
If you are some how irritated by seeing these postings you are free
to ignore them or add the sender to your killfile. If you find
errors or other problems with these postings please send corrections
or comments to the posting email address or to the maintainers as
directed in the perlfaq manual page.
Note that the FAQ text posted by this server may have been modified
from that distributed in the stable Perl release. It may have been
edited to reflect the additions, changes and corrections provided
by respondents, reviewers, and critics to previous postings of
these FAQ. Complete text of these FAQ are available on request.
The perlfaq manual page contains the following copyright notice.
AUTHOR AND COPYRIGHT
Copyright (c) 1997-2002 Tom Christiansen and Nathan
Torkington, and other contributors as noted. All rights
reserved.
This posting is provided in the hope that it will be useful but
does not represent a commitment or contract of any kind on the part
of the contributers, authors or their agents.
.
- Prev by Date: Re: HTTP::Request/GET response not expected
- Next by Date: Re: Filling the Perl Stack
- Previous by thread: Suggestion for name of TLC engineering module
- Next by thread: FAQ 4.64 How can I get the unique keys from two hashes?
- Index(es):
Relevant Pages
|
|
