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MathGroup Archive 2002

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RE: random integer weirdness

  • To: mathgroup at smc.vnet.net
  • Subject: [mg35787] RE: [mg35772] random integer weirdness
  • From: "DrBob" <majort at cox-internet.com>
  • Date: Wed, 31 Jul 2002 01:33:24 -0400 (EDT)
  • Reply-to: <drbob at bigfoot.com>
  • Sender: owner-wri-mathgroup at wolfram.com

That IS bizarre.  The following works much better, though it may have
other statistical problems:

sim = Table[{j, Mean[Table[Ceiling[Random[]2^j], {n}]]
              2^(1 - j)}, {j, 45, 65, 1/8}];
ListPlot[sim];

Bobby Treat

-----Original Message-----
From: Mark Fisher [mailto:mark at markfisher.net] 
To: mathgroup at smc.vnet.net
Subject: [mg35787] [mg35772] random integer weirdness

There is some real weirdness with Random[Integer, j] for some large
values of j but not others (for both 4.1 and 4.2 versions).

<<Statistics`
n = 1000;
sim = Table[{j, (2/2^j) * Mean[Table[Random[Integer, 2^j], {n}]]}, 
      {j, 45, 65, 1/8}];
ListPlot[sim];

All the points should be near one if the random number generator were
working properly. What gives? Is this just a (very stark) symptom of
what Daniel Lichtblau mentioned in his May 2000 post?

>> The other failure only is apparent in very large big
>> integers, and I do not know exactly how to categorize it.

I just find this very troubling.

--Mark.





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