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Re: srand(0)

From	David Brown <david.brown@hesbynett.no>
Newsgroups	sci.math.num-analysis, comp.lang.c
Subject	Re: srand(0)
Date	2026-02-19 20:47 +0100
Organization	A noiseless patient Spider
Message-ID	<10n7pct$3puc5$1@dont-email.me> (permalink)
References	(11 earlier) <20260203163708.0000459e@yahoo.com> <86y0kqfq85.fsf@linuxsc.com> <10n47bi$2io53$3@dont-email.me> <10n6jgg$3bj7e$1@dont-email.me> <10n7oie$289ca$2@dont-email.me>

Cross-posted to 2 groups.

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On 19/02/2026 20:33, James Kuyper wrote:
> On 2026-02-19 04:01, David Brown wrote:
>> On 18/02/2026 12:21, Tristan Wibberley wrote:
>>> On 18/02/2026 07:47, Tim Rentsch wrote:
>>>
>>>> The key property of a (pseudo) random number generator is that the
>>>> values produced exhibit no discernible pattern.
>>>
>>> For a PRNG, they exhibit the pattern of following the sequence of the PRNG!
>>>
>>
>> As a deterministic function, a PRNG will obviously follow the pattern of
>> its generating function.  But the aim is to have no /discernible/
>> pattern.  The sequence 3, 4, 2, 1, 1, 7, 0, 6, 7 has no pattern that
>> could be identified without knowledge of where they came from - and thus
>> no way to predict the next number, 9, in the sequence.  But there is a
>> pattern there - it's the 90th - 100th digits of the decimal expansion of pi.
> 
> I think you're being overoptimistic. I suspect that the pattern could be
> identified, exactly, without knowing how it was generated. That's
> because every possible pattern has infinitely many different ways in
> which in can be produced. One of those other ways might be easier to
> describe than the way in which the numbers were actually produced, in
> which case that simpler way might be guessed more easily that the actual
> one - possibly a lot easier.

How likely is it that someone would guess a formula that happened to 
generate the decimal digits of pi, without more knowledge than a part of 
the sequence?  I don't believe it is possible to quantify such a 
probability, but I would expect it to be very low.

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Re: srand(0) Tristan Wibberley <tristan.wibberley+netnews2@alumni.manchester.ac.uk> - 2026-02-18 11:21 +0000
  Re: srand(0) David Brown <david.brown@hesbynett.no> - 2026-02-19 10:01 +0100
    Re: srand(0) James Kuyper <jameskuyper@alumni.caltech.edu> - 2026-02-19 14:33 -0500
      Re: srand(0) David Brown <david.brown@hesbynett.no> - 2026-02-19 20:47 +0100
        Re: srand(0) James Kuyper <jameskuyper@alumni.caltech.edu> - 2026-02-20 16:01 -0500
          Re: srand(0) David Brown <david.brown@hesbynett.no> - 2026-02-21 11:09 +0100
    Re: srand(0) Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2026-02-19 14:39 -0800
      Re: srand(0) David Brown <david.brown@hesbynett.no> - 2026-02-20 09:16 +0100
        Re: srand(0) Paul <nospam@needed.invalid> - 2026-02-23 08:32 -0500
          Re: srand(0) David Brown <david.brown@hesbynett.no> - 2026-02-23 16:05 +0100
            Re: srand(0) Michael S <already5chosen@yahoo.com> - 2026-02-23 19:59 +0200
              Re: srand(0) David Brown <david.brown@hesbynett.no> - 2026-02-23 20:06 +0100
                Re: srand(0) Paul <nospam@needed.invalid> - 2026-02-23 15:24 -0500
                Re: srand(0) Axel Reichert <mail@axel-reichert.de> - 2026-02-24 07:08 +0100
                Re: srand(0) David Brown <david.brown@hesbynett.no> - 2026-02-24 10:24 +0100
                Re: srand(0) Axel Reichert <mail@axel-reichert.de> - 2026-02-26 19:13 +0100
                Re: srand(0) Michael S <already5chosen@yahoo.com> - 2026-02-24 18:36 +0200
                Re: srand(0) Axel Reichert <mail@axel-reichert.de> - 2026-02-24 20:00 +0100
                Re: srand(0) Tristan Wibberley <tristan.wibberley+netnews2@alumni.manchester.ac.uk> - 2026-02-24 18:00 +0000

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