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Re: The Basics: What is Compressibility?

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SG <s.gesemann@gmail.com> wrote:

(snip)
>> Well, some of them are easy. If you group the data into groups of
>> some number of bits, such as bytes or words, you can easily compute
>> the entropy, and so the compressibility, of those groups. Often the
>> entropy of one grouping, such as groups of seven bits,  will also extend
>> other groupings, such as bytes.
 
> "the entropy" of what? -- Of an assumed source model based on
> estimated probabilities. And that goes back to what I tried to say
> about "sources" and "information". ;-)

Yes, I didn't say it very well.

If you only consider the frequency of bit groups (such as bytes)
and nothing else, you can compute how compressible the data stream
is based only on that. That is most useful when the data is a stream
of uncorrelated data, for example coin flips or dice rolls.
(Loaded dice rolls will be more compressible than fair dice.)

Other than that specific case, one should not expect to write a 
general compression algorithm without knowing more about the source.
So, yes, the difference between "sources" and "information".

-- glen

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The Basics: What is Compressibility? Ernst <Ernst_Berg@sbcglobal.net> - 2013-04-14 17:20 -0700
  Re: The Basics: What is Compressibility? SG <s.gesemann@gmail.com> - 2013-04-15 08:40 -0700
    Re: The Basics: What is Compressibility? glen herrmannsfeldt <gah@ugcs.caltech.edu> - 2013-04-15 18:57 +0000
      Re: The Basics: What is Compressibility? SG <s.gesemann@gmail.com> - 2013-04-16 02:11 -0700
        Re: The Basics: What is Compressibility? glen herrmannsfeldt <gah@ugcs.caltech.edu> - 2013-04-16 19:37 +0000
    Re: The Basics: What is Compressibility? Thomas Richter <thor@math.tu-berlin.de> - 2013-04-16 09:19 +0200
      Re: The Basics: What is Compressibility? SG <s.gesemann@gmail.com> - 2013-04-16 02:49 -0700
  Re: The Basics: What is Compressibility? James Dow Allen <jdallen2000@yahoo.com> - 2013-04-15 23:12 -0700
    Re: The Basics: What is Compressibility? Thomas Richter <thor@math.tu-berlin.de> - 2013-04-16 09:09 +0200
      Re: The Basics: What is Compressibility? James Dow Allen <jdallen2000@yahoo.com> - 2013-04-16 09:04 -0700
        Re: The Basics: What is Compressibility? Thomas Richter <thor@math.tu-berlin.de> - 2013-04-16 19:47 +0200
      Re: The Basics: What is Compressibility? lawcounsels@gmail.com - 2013-04-18 05:08 -0700
        Re: The Basics: What is Compressibility? James Dow Allen <jdallen2000@yahoo.com> - 2013-04-18 06:14 -0700
          Re: The Basics: What is Compressibility? LawCounsels <LawCounsels@aol.com> - 2013-04-19 06:41 -0700
            Re: The Basics: What is Compressibility? Thomas Richter <thor@math.tu-berlin.de> - 2013-04-20 08:48 +0200
    Re: The Basics: What is Compressibility? SG <s.gesemann@gmail.com> - 2013-04-16 02:36 -0700
  Re: The Basics: What is Compressibility? Ernst <Ernst_Berg@sbcglobal.net> - 2013-04-19 18:33 -0700
  Re: The Basics: What is Compressibility? Ernst <Ernst_Berg@sbcglobal.net> - 2013-04-19 18:55 -0700
  Re: The Basics: What is Compressibility? Ernst <Ernst_Berg@sbcglobal.net> - 2013-04-23 16:31 -0700
  Re: The Basics: What is Compressibility? Ernst <Ernst_Berg@sbcglobal.net> - 2013-04-23 18:32 -0700
  Re: The Basics: What is Compressibility? Ernst <Ernst_Berg@sbcglobal.net> - 2013-05-01 17:14 -0700
  Re: The Basics: What is Compressibility? Ernst <Ernst_Berg@sbcglobal.net> - 2013-05-13 15:52 -0700

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