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Article #13Re: entropy
From: Harald Hanche-Olsen
Date: Wed, 13 Oct 1999 00:00
Date: Wed, 13 Oct 1999 00:00
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+ "Simon" <s.salm@cable.a2000.nl>:
| X is a discrete random variable that takes on one of the values x1, x2,
| ..... , xn, with respective probabilities p1, p2, .... ,pn.
|
| The entropy of X is defined as: H(X) = -Sum{pi*log(pi)} in which log
| means log with base 2 and Sum means summation over all i.
|
| Please, could someone explain to me why H(X) is maximized when all
| of the pi are equal?? (It is quite easy to prove when n=2)(But what
| to do when n>2???)
If your library has a copy of the book "Information theory and coding"
by Norman Abramson (it's from 1963, so it may be hidden away in the
basement), you can find a clear explanation there. Otherwise, you can
do it yourself, by using the Lagrange multiplier method on the sum
with the constraint Sum{pi}=1. But the book is a good read if you can
get hold of it.
--
* Harald Hanche-Olsen <URL:http://www.math.ntnu.no/~hanche/>
- "There arises from a bad and unapt formation of words
a wonderful obstruction to the mind." - Francis Bacon
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X-Google-Language: ENGLISH,ASCII-7-bit X-Google-Thread: 1032cb,a1b4de0cf05f260e X-Google-Attributes: gid1032cb,public X-Google-Thread: 10d29f,a1b4de0cf05f260e X-Google-Attributes: gid10d29f,public X-Google-Thread: 10d67e,a1b4de0cf05f260e X-Google-Attributes: gid10d67e,public From: Harald Hanche-Olsen <hanche@math.ntnu.no> Subject: Re: entropy Date: 1999/10/13 Message-ID: <pcohfjvi3ss.fsf@martens.math.ntnu.no> X-Deja-AN: 536318594 Approved: Daniel Grayson, dan@math.uiuc.edu, moderator for sci.math.research References: <7u0bf5$4k3$1@tesla.a2000.nl> X-Complaints-To: usenet@itea.ntnu.no X-Trace: kopp.stud.ntnu.no 939834709 18583 129.241.15.250 (13 Oct 1999 17:11:49 GMT) Organization: Norwegian university of science and technology NNTP-Posting-Date: 13 Oct 1999 17:11:49 GMT Newsgroups: de.sci.mathematik,aus.mathematics,sci.math.research Originator: dan@orion.math.uiuc.edu