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Why aren't my random numbers random?

by faq_monk (Initiate)
on Oct 08, 1999 at 00:20 UTC ( #584=perlfaq nodetype: print w/replies, xml ) Need Help??

Current Perl documentation can be found at perldoc.perl.org.

Here is our local, out-dated (pre-5.6) version:

The short explanation is that you're getting pseudorandom numbers, not random ones, because computers are good at being predictable and bad at being random (despite appearances caused by bugs in your programs :-). A longer explanation is available on http://www.perl.com/CPAN/doc/FMTEYEWTK/random, courtesy of Tom Phoenix. John von Neumann said, ``Anyone who attempts to generate random numbers by deterministic means is, of course, living in a state of sin.''

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://nr.harvard.edu/nr/bookc.html .

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[ambrus]: My boss wants to generate output data that is impossible to compute from the inputs we have. And I'm trying to convince him that he shouldn't do that.

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