POV-Ray : Newsgroups : povray.off-topic : Infinite sequences and probability : Re: Infinite sequences and probability Server Time
29 Sep 2024 17:19:25 EDT (-0400)
  Re: Infinite sequences and probability  
From: Kevin Wampler
Date: 28 Apr 2009 14:33:45
Message: <49f74c09$1@news.povray.org>
Mueen Nawaz wrote:
> 	Put another way, I showed that the even if I allow some sequences with
> a single 1 to sneak in, the probability is still 0.

Oh yeah, I certainly wasn't debating the accuracy of the result.  It 
appears that you already considered this detail anyway, so my 
nit-picking was entirely unnecessary.

I did like the Cantor set analogy by the way.  I didn't forsee it when I 
was reading your post and was delighted when you pointed it out.

> 
>> I think represent the same number on the real line, but one would be in
>> the set and one wouldn't.  Nevertheless I do think that the Cantor set
> 
> 	One would be in the set of sequences we're interested in, and the other
> wouldn't. In terms of the Cantor set, they're both in it as they are the
> same number.

Yeah, that's what I meant.

>>     lim_{n->inf} a^n = 0 if 0 <= a < 1
> 
> 	(Incidentally, I'm not sure I understand your limit. What is 'a' and
> why is it fixed?

For base m a would be (m-1)/m -- the probability that a single given 
digit of the random sequence doesn't contain a 1 in base m.

>> 1 = sum_{0:inf} p
>>
>> Since no real number has this property, p cannot exist.  Thus there is
>> no probability (zero or otherwise) that a random sequence is in S.  Said
>> in more standard terminology: S has no measure.
> 
> 	I didn't read the whole thing - xors make my head hurt. But I got the
> general idea, having seen similar arguments before. When I was learning
> integration theory using measures, I noticed that integrals were always
> defined over _measurable_ sets.

In that case I'll spare you the trouble of being tempted to read it 
later.  I just adapted the construction of a Vitali set from the real 
line to infinite binary sequences by replacing addition with xor.  A few 
small things changed as a result, but nothing major.

I'm enveious you had an integration theory class that got into measure 
theory.  I don't recall such a course being available back when I was 
taking math classes, but it would have been pretty fun had there been.


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