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#1 2013-02-25 08:33:05

genericname
Member
Registered: 2012-05-16
Posts: 52

Log question

(2*(n/2)*lg(n/2)) + n

= (n*lg(n/2))+n

= n*(lg n - 1) + n

How does (n*lg(n/2))+n simplify to n*(lg n - 1) + n? What happened to the n/2 that was inside? It has been a while since I last worked with log.

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#2 2013-02-25 08:50:27

bobbym
Administrator
From: Bumpkinland
Registered: 2009-04-12
Posts: 86,776

Re: Log question

Hi;

Is this the problem?

Last edited by bobbym (2013-02-25 08:51:47)


In mathematics, you don't understand things. You just get used to them.
Of course that result can be rigorously obtained, but who cares?
Combinatorics is Algebra and Algebra is Combinatorics.

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#3 2013-02-25 08:58:06

genericname
Member
Registered: 2012-05-16
Posts: 52

Re: Log question

Yeah.

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#4 2013-02-25 10:10:06

bobbym
Administrator
From: Bumpkinland
Registered: 2009-04-12
Posts: 86,776

Re: Log question

I am getting:

Last edited by bobbym (2013-02-25 10:10:52)


In mathematics, you don't understand things. You just get used to them.
Of course that result can be rigorously obtained, but who cares?
Combinatorics is Algebra and Algebra is Combinatorics.

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#5 2013-02-25 13:40:36

anonimnystefy
Real Member
From: The Foundation
Registered: 2011-05-23
Posts: 15,532

Re: Log question

Hi genericname

lg(a/b)=lg(a)-lg(b) for any a and b for which the expression is defined.

So, lg(n/2)=lg(n)-lg(2)=lg(n)-1, assuming the logarithm is with base 2.


“Here lies the reader who will never open this book. He is forever dead.

“Taking a new step, uttering a new word, is what people fear most.” ― Fyodor Dostoyevsky, Crime and Punishment

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#6 2013-02-25 14:27:50

bobbym
Administrator
From: Bumpkinland
Registered: 2009-04-12
Posts: 86,776

Re: Log question

Why would the log be to the base two?


In mathematics, you don't understand things. You just get used to them.
Of course that result can be rigorously obtained, but who cares?
Combinatorics is Algebra and Algebra is Combinatorics.

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#7 2013-02-25 14:41:10

anonimnystefy
Real Member
From: The Foundation
Registered: 2011-05-23
Posts: 15,532

Re: Log question

Because then the step makes sense. We will have have to wait for the OP's answer.

And besides, the use of n and lg reminds me of comp. analysis.

Last edited by anonimnystefy (2013-02-25 14:42:40)


“Here lies the reader who will never open this book. He is forever dead.

“Taking a new step, uttering a new word, is what people fear most.” ― Fyodor Dostoyevsky, Crime and Punishment

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#8 2013-02-25 16:31:10

bobbym
Administrator
From: Bumpkinland
Registered: 2009-04-12
Posts: 86,776

Re: Log question

A very good answer!


In mathematics, you don't understand things. You just get used to them.
Of course that result can be rigorously obtained, but who cares?
Combinatorics is Algebra and Algebra is Combinatorics.

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#9 2013-02-26 03:44:16

genericname
Member
Registered: 2012-05-16
Posts: 52

Re: Log question

Ah, thank you. It was base 2, sorry for the confusion.

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#10 2013-02-26 06:19:58

anonimnystefy
Real Member
From: The Foundation
Registered: 2011-05-23
Posts: 15,532

Re: Log question

No problem and you're welcome!


“Here lies the reader who will never open this book. He is forever dead.

“Taking a new step, uttering a new word, is what people fear most.” ― Fyodor Dostoyevsky, Crime and Punishment

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