Re: [gentoo-user] Re: OT: Mapping random numbers (PRNG)

[Canek Peláez Valdés]

On Sat, Jun 28, 2014 at 8:46 PM, »Q« <boxcars@×××.net> wrote:
> On Sat, 28 Jun 2014 19:53:08 -0500
> Canek Peláez Valdés <caneko@×××××.com> wrote:
>
>> On Sat, Jun 28, 2014 at 7:37 PM,  <gottlieb@×××.edu> wrote:
>> > On Sat, Jun 28 2014, Canek Peláez Valdés wrote:
>> >
>> >> That doesn't matter. Take a non-negative integer N; if you flip a
>> >> coin an infinite number of times, then the probability of the coin
>> >> landing on the same face N times in a row is 1.
>> >
>> > This is certainly true.
>> >
>> >> This means that it is *guaranteed* to happen
>> >
>> > That is not as clear.
>>
>> Let me be more precise (and please correct me if I'm wrong): It is
>> guaranteed to happen at some point in the infinite sequence of random
>> flip coins, but we cannot know when it will happen, only that it will
>> happen.
>>
>> That's the way I got it when I took my probability courses, admittedly
>> many years ago.
>
> The probability is 1 in the sense that the as the number of flips M
> increases, so does the probability of getting N heads (or tails) in a
> row also increases, and the upper bound for the sequence of
> probabilities is 1.  It's not a probability about something which
> actually happens;  no one so far has been able to flip a coin an
> infinite number of times, not even a computer.

And no one will. Ever.

>> In any way, even if I'm wrong and it is not guaranteed, the main point
>> remains true: the probability of getting a large sequence of the same
>> number from a RNG is 1 for every true random RNG, and therefore seeing
>> a large sequence of the same number form a RNG doesn't (technically)
>> means that it is broken.
>
> It's true that that wouldn't *prove* the generator is broken.  But it
> might be a good reason to take another look at the algorithm.

Agreed.

Regards.
-- 
Canek Peláez Valdés
Profesor de asignatura, Facultad de Ciencias
Universidad Nacional Autónoma de México