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MathGroup Archive 2005

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Re: Re: Simplify problems for checking easy equalities...

  • To: mathgroup at smc.vnet.net
  • Subject: [mg53938] Re: [mg53886] Re: Simplify problems for checking easy equalities...
  • From: yehuda ben-shimol <benshimo at bgu.ac.il>
  • Date: Fri, 4 Feb 2005 04:12:21 -0500 (EST)
  • References: <ctnhah$erh$1@smc.vnet.net> <200502021125.GAA28962@smc.vnet.net>
  • Sender: owner-wri-mathgroup at wolfram.com

Kevin,
note that for example
Log[x^n] - n*Log[x] /. {n -> -4, x -> -2}
will return
4*(I*Pi + Log[2]) - Log[16]
certainly not 0
yehuda

Kevin J. McCann wrote:

>David,
>
>While your approach works, the identity is true regardless of the values 
>of x and n; so, it is curious that Simplify does not get it for the more 
>general case.
>
>Kevin
>
>David Park wrote:
>  
>
>>Cyrus,
>>
>>Include the proper assumptions in the Simplify statement.
>>
>>Simplify[Log[x^n] - n*Log[x], n \[Element] Integers && x > 0]
>>0
>>
>>David Park
>>djmp at earthlink.net
>>http://home.earthlink.net/~djmp/ 
>>
>>From: Cyrus Erik Eierud [mailto:cyruserik at tele2.se]
To: mathgroup at smc.vnet.net
>>    
>>
>To: mathgroup at smc.vnet.net
>  
>
>>Please Help!
>>
>>Thanks for all great answers I've already found here!
>>My problem is that I can not simplify what to me seems as a very
>>simple equality task. This is what I want Mathematica to return zero
>>for:
>>
>>in[1]:= FullSimplify[Log[x^n] - n*Log[x]]
>>
>>out[1]= -n Log[x] + Log[x^n])
>>
>>I have used Simplify to check equalities, but the one above (and many
>>other equations similar to the one above) just don't simplify. Am I
>>doing anything wrong or does anyone know of a better way to check
>>equalities?
>>
>>Appreciate any help,
>>Cyrus Eierud, Student
>>cyruserik at tele2.se
>>


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