Re: Random data cannot be compressed

Steve Schafer said:

<snip>
 
> Look, I have no vested interest in the (in)compressibility of random
> data.

Neither do I, as it happens. Just shootin' the breeze.

> This whole discussion is nonsense about nonsense.

While we're on the subject of nonsense, and since you seem (more or less) 
to grok what I'm on about, here's a little curiosity for you. I've 
generated quite a few 48-bit strings during the course of this discussion,

mostly by tossing coins about the place. (Sad, or what?) I ended up not 
using any of them in the discussion (typical!), but... Well, here's a 
perfectly genuine bit string constructed from the result of coin tossing:

000101101101000001010011100101110111010001011110

There's something rather astonishing about it. I'm not saying it's 
compressible-without-cheating (it's too short for that, I think), but it 
does have a very interesting property that I *know* is the result of 
randomness but which I, being human and reasonably numerate, still find 
quite hard to accept as random.

Rot-13'd hint: Tenpr Ubccre jbhyq unir fcbggrq guvf cnggrea rnfvyl,
creuncf 
juvyfg onynapvat ure purdhrobbx.



> I am well aware
> of the definitions of randomness and why random data cannot be
> compressed in general (and also why no compression algorithm can
> compress all data sets).

Um, so am I, actually. Well, I won't fight anyone over the definition of 
randomness, since I'm no mathematician, but as a programmer I understand 
all about overhead so I know why the general case is as it is. But I do 
know perfectly well that, just as the media /can/ occasionally get the 
facts right, so random processes /can/ occasionally generate compressible 
data - and for much the same reason, alas.


> The only reason that I got involved at all is
> because Richard is playing you, and probably laughing his head off while
> at it.

Well, maybe a bit. I think that what's happened here is that he probably 
didn't realise that he'd made an astoundingly wrong statement, and now 
he's defending what he thought he said, rather than what he actually said.

And it's no good trotting out what he actually said (although I have done 
so a couple of times now) because, no matter how many times he reads it, 
he'll still read it as if it meant what he wants it to mean. I sympathise,

because I've been through that loop a few times myself over the years - 
but he's still wrong. Well, okay, let's clarify that - his underlying 
understanding of the subject matter is obviously fine, and I am pretty 
certain that the point he /thinks/ he's making is correct. But the point 
he's actually making is not.

-- 
Richard Heathfield <http://www.cpax.org.uk>
Email: -http://www.
+rjh@[EMAIL PROTECTED]
 users: <http://www.cpax.org.uk/prg/writings/googly.php>
"Usenet is a strange place" - dmr 29 July 1999