Re: Compare two methods of random permutations

From	Mok-Kong Shen <mok-kong.shen@t-online.de>
Newsgroups	comp.programming
Subject	Re: Compare two methods of random permutations
Date	2013-05-17 14:11 +0200
Organization	albasani.net
Message-ID	<kn56po$83m$1@news.albasani.net> (permalink)
References	(10 earlier) <925e0863-2757-4c0f-881b-b169be8d5c35@h9g2000pbr.googlegroups.com> <csSdndTRgvcICg7MnZ2dnUVZ_vednZ2d@earthlink.com> <5f7c6014-dde2-4604-9f30-c544f3a336bb@k8g2000pbf.googlegroups.com> <O-CdnaNSZ9AA9wnMnZ2dnUVZ8gudnZ2d@bt.com> <cc477dbf-401f-4e44-b52b-1a2c8756f091@tz3g2000pbb.googlegroups.com>

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Am 16.05.2013 10:35, schrieb James Dow Allen:
> On May 16, 12:10 pm, "Chris Uppal" <chris.up...@metagnostic.REMOVE-
> THIS.org> wrote:
>> James Dow Allen wrote:
>>> Note that the code snippet I posted assures, via
>>>           do a = rand();
>>>          while (a >= 1916006400);
>>> that the requirements are met throughout.
>>
>> Missed that aspect of it myself.  Shows the value of comments in code...
>
> I could have written
>          // 5 * 12! would be too large -- overflows RANDMAX
>          while (a >= 4 * (12*11*10*9*8*7*6*5*4*3*2));
> Sorry.  Still, making excuses for the inexcusable, an
> alert reader would have wondered why the "while a>= " is present
> at all.  Perhaps I forgot I wasn't posting in rec.puzzles.  :-)
>
> My "real code" for such is quite different:
> 1) One wants to handle arbitrary random sizes, not
> just 12,11,10,9, ... specifically.
> 2) The sample code discards unused 11% of its random
> inputs.  Not only can that be reduced, but *some* of the
> random "entropy" can be preserved even on the discards.
>
> I don't know how important such coding is.
> The twiddling sacrifices much of the time saved by fewer
> calls to random().  Still I will post more general routines
> if there's interest.  Please tell me if most people use
> 31-bit generators (Posix?) or 32-bit generators (Marsaglia).
> Yes, I know about "#ifdef" -- I just don't like to
> post cluttered code.

I suppose one has first to know in which range is rand()
(assumed to be) a uniformly distributed random variable. Could
you tell? Further, could you at least give a sketch of what you
indicated to be more general constructs of your design?

M. K. Shen

Thread

Compare two methods of random permutations Mok-Kong Shen <mok-kong.shen@t-online.de> - 2013-05-08 23:35 +0200
  Re: Compare two methods of random permutations James Dow Allen <jdallen2000@yahoo.com> - 2013-05-11 21:31 -0700
    Re: Compare two methods of random permutations Mok-Kong Shen <mok-kong.shen@t-online.de> - 2013-05-13 08:07 +0200
      Re: Compare two methods of random permutations James Dow Allen <jdallen2000@yahoo.com> - 2013-05-13 02:34 -0700
  Re: Compare two methods of random permutations Mok-Kong Shen <mok-kong.shen@t-online.de> - 2013-05-13 08:01 +0200
  Re: Compare two methods of random permutations bob <bob@coolfone.comze.com> - 2013-05-13 08:26 -0700
    Re: Compare two methods of random permutations James Dow Allen <jdallen2000@yahoo.com> - 2013-05-13 11:42 -0700
      Re: Compare two methods of random permutations bob <bob@coolfone.comze.com> - 2013-05-16 13:46 -0700
    Re: Compare two methods of random permutations Mok-Kong Shen <mok-kong.shen@t-online.de> - 2013-05-13 21:09 +0200
      Re: Compare two methods of random permutations bob <bob@coolfone.comze.com> - 2013-05-13 12:57 -0700
        Re: Compare two methods of random permutations Mok-Kong Shen <mok-kong.shen@t-online.de> - 2013-05-13 22:59 +0200
          Re: Compare two methods of random permutations bob <bob@coolfone.comze.com> - 2013-05-13 15:28 -0700
            Re: Compare two methods of random permutations Mok-Kong Shen <mok-kong.shen@t-online.de> - 2013-05-14 10:54 +0200
              Re: Compare two methods of random permutations James Dow Allen <jdallen2000@yahoo.com> - 2013-05-14 05:32 -0700
                Re: Compare two methods of random permutations Mok-Kong Shen <mok-kong.shen@t-online.de> - 2013-05-14 22:46 +0200
                Re: Compare two methods of random permutations James Dow Allen <jdallen2000@yahoo.com> - 2013-05-14 14:19 -0700
                Re: Compare two methods of random permutations James Dow Allen <jdallen2000@yahoo.com> - 2013-05-14 15:06 -0700
                Re: Compare two methods of random permutations Mok-Kong Shen <mok-kong.shen@t-online.de> - 2013-05-15 10:16 +0200
                Re: Compare two methods of random permutations James Dow Allen <jdallen2000@yahoo.com> - 2013-05-15 03:54 -0700
                Re: Compare two methods of random permutations Patricia Shanahan <pats@acm.org> - 2013-05-15 07:11 -0700
                Re: Compare two methods of random permutations James Dow Allen <jdallen2000@yahoo.com> - 2013-05-15 11:04 -0700
                Re: Compare two methods of random permutations James Dow Allen <jdallen2000@yahoo.com> - 2013-05-15 11:06 -0700
                Re: Compare two methods of random permutations Patricia Shanahan <pats@acm.org> - 2013-05-15 12:55 -0700
                Re: Compare two methods of random permutations "Chris Uppal" <chris.uppal@metagnostic.REMOVE-THIS.org> - 2013-05-16 06:10 +0100
                Re: Compare two methods of random permutations pacman@kosh.dhis.org (Alan Curry) - 2013-05-16 06:57 +0000
                Re: Compare two methods of random permutations "Chris Uppal" <chris.uppal@metagnostic.REMOVE-THIS.org> - 2013-05-16 09:26 +0100
                Re: Compare two methods of random permutations James Dow Allen <jdallen2000@yahoo.com> - 2013-05-16 01:35 -0700
                Re: Compare two methods of random permutations Mok-Kong Shen <mok-kong.shen@t-online.de> - 2013-05-17 14:11 +0200
                Re: Compare two methods of random permutations James Dow Allen <jdallen2000@yahoo.com> - 2013-05-17 08:13 -0700
                Re: Compare two methods of random permutations Mok-Kong Shen <mok-kong.shen@t-online.de> - 2013-05-19 11:06 +0200
                Re: Compare two methods of random permutations James Dow Allen <jdallen2000@yahoo.com> - 2013-05-19 03:14 -0700
                Re: Compare two methods of random permutations Mok-Kong Shen <mok-kong.shen@t-online.de> - 2013-05-19 13:26 +0200
                Re: Compare two methods of random permutations James Dow Allen <jdallen2000@yahoo.com> - 2013-05-19 04:59 -0700
                Re: Compare two methods of random permutations Mok-Kong Shen <mok-kong.shen@t-online.de> - 2013-05-19 14:13 +0200
                Re: Compare two methods of random permutations James Dow Allen <jdallen2000@yahoo.com> - 2013-05-19 05:52 -0700
                Re: Compare two methods of random permutations Mok-Kong Shen <mok-kong.shen@t-online.de> - 2013-05-19 15:06 +0200
                Re: Compare two methods of random permutations James Dow Allen <jdallen2000@yahoo.com> - 2013-05-19 06:50 -0700
                Re: Compare two methods of random permutations Mok-Kong Shen <mok-kong.shen@t-online.de> - 2013-05-19 16:14 +0200
                Re: Compare two methods of random permutations James Dow Allen <jdallen2000@yahoo.com> - 2013-05-19 08:11 -0700
                Re: Compare two methods of random permutations Mok-Kong Shen <mok-kong.shen@t-online.de> - 2013-05-19 17:15 +0200
                Re: Compare two methods of random permutations Mok-Kong Shen <mok-kong.shen@t-online.de> - 2013-05-19 17:24 +0200

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