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 > >> > >> > >> > >