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Subject: Re: The problem with big-O is one of definitions

Author: Ricardo Gibert

Date: 16:23:45 05/09/01

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On May 09, 2001 at 18:16:48, Dann Corbit wrote:

>Some people are insisting that finite inputs mean O(1).
>
>My insistence is that the big-O behavior should model the difference from n to
>n+1 and from n to n-1 (past some point n0).


Definition: f(n) = O(g(n)) (read as "f of n equals big oh of g of n") iff there
exists two positive constants c and n_0 sth |f(n)| <= c*|g(n)| for all n >= n_0.

I see nothing in the above definition that talks about "n to n+1 and from n to
n-1".

I do see that n is unbounded. I also note that in chess, n *is* bounded unless
you generalize 8*8 chess to n*n chess when n is then unbounded. If you make such
a generalization, you can conclude that n*n chess is O(exp(n)). You can then
instantiate it to the 8*8 case to obtain a usable result, but please do not say
that 8*8 chess is O(exp(n)) rather than say n*n chess is O(exp(n)).
I don't see this can be made more clear. I'm really at a loss as to why you
cannot interpret formal definitions correctly.


>
>There are no real algorithms with infinite inputs.   These so-called algorithms
>can never terminate.


I never said anything about infinite inputs. "Unbounded" is not the same as
"infinite". Get the terminology straight or you will get nowhere.


>
>Because we cannot agree on definitions we can never come to an agreement.  My
>definitions are the classiscal defintions used in all the literature.  The
>alternative definitions make for interesting debate, but since they have no
>value at predictions, they have no practical value.



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