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MathGroup Archive 2005

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Re: Simplify problems for checking easy equalities...

  • To: mathgroup at smc.vnet.net
  • Subject: [mg53860] Re: Simplify problems for checking easy equalities...
  • From: "Drago Ganic" <drago.ganic at in2.hr>
  • Date: Tue, 1 Feb 2005 04:08:10 -0500 (EST)
  • References: <cti5nd$8n2$1@smc.vnet.net>
  • Sender: owner-wri-mathgroup at wolfram.com

Hi Cyrus,
use assumptions! The simplification qou expect is not generally valid.
Simplify or Refine are enough for the elementary functions!

FullSimplify[Log[x^n] - n Log[x], n \[Element] Integers && x > 0]
0

Simplify[Log[x^n] - n*Log[x], n \[Element] Integers && x > 0]
0

Refine[Log[x^n] - n*Log[x], n \[Element] Integers && x > 0]
0

Those assumptions are used implicity in the unary function PowerExpand:
Log[x^n] - n*Log[x] // PowerExpand
0

Greetings,
Drago
"Cyrus Erik Eierud" <cyruserik at tele2.se> wrote in message 
news:cti5nd$8n2$1 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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