On 28 Dec 2013, at 22:23, meekerdb wrote:
On 12/28/2013 4:09 AM, Bruno Marchal wrote:
For a long time I got opponent saying that we cannot generate
computationally a random number, and that is right, if we want
generate only that numbers. but a simple counting algorithm
generating all numbers, 0, 1, 2, .... 6999500235148668, ...
generates all random finite incompressible strings,
How can a finite string be incompressible? 6999500235148668 in base
6999500235148669 is just 10.
You can define a finite string as incompressible when the shorter
combinators to generate it is as lengthy as the string itself.
This definition is not universal for a finite amount of short
sequences which indeed will depend of the language used (here
combinators).
Then you can show that such a definition can be made universal by
adding some constant, which will depend of the universal language.
It can be shown that most (finite!) numbers, written in any base, are
random in that sense.
Of course, 10 is a sort of compression of any string X in some base,
but if you allow change of base, you will need to send the base with
the number in the message. If you fix the base, then indeed 10 will be
a compression of that particular number base, for that language, and
it is part of incompressibility theory that no definition exist
working for all (small) numbers. Each particular language will have
some exception on the incompressibility issue. That should be part of
the role of the variable constant in the general universal definition.
Bruno
http://iridia.ulb.ac.be/~marchal/
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