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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: [mg54131] Re: Simplify problems for checking easy equalities...
  • From: cyruserik at tele2.se (Cyrus Erik Eierud)
  • Date: Fri, 11 Feb 2005 03:33:53 -0500 (EST)
  • References: <ctvfov$1bp$1@smc.vnet.net>
  • Sender: owner-wri-mathgroup at wolfram.com

Thanks for all your answers!
Now I can craft my equations with confidence in Mathematica again :-)

/Cyrus

Bill Rowe <readnewsciv at earthlink.net> wrote in message news:<ctvfov$1bp$1 at smc.vnet.net>...
> On 2/2/05 at 6:25 AM, kjm at KevinMcCann.com (Kevin J. McCann) wrote:
> 
> >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.
> 
> No, the identity is not true regardless of the values of x and n. For a specific counter example, choose x = -1 and n = 2. The Log[x^n] = Log[1] = 0 and n Log[x] = 2 Log[-1] = 2 Pi I which is clearly not 0.
> 
> >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
> >>
> >>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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