Re: Simplify problems for checking easy equalities...

*To*: mathgroup at smc.vnet.net*Subject*: [mg53865] Re: Simplify problems for checking easy equalities...*From*: Bill Rowe <readnewsciv at earthlink.net>*Date*: Tue, 1 Feb 2005 04:08:15 -0500 (EST)*Sender*: owner-wri-mathgroup at wolfram.com

On 1/30/05 at 3:18 AM, cyruserik at tele2.se (Cyrus Erik Eierud) wrote: >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? You are not doing something wrong. The reason FullSimplify and Simplify don't work here is that Log[x^n] isn't equal to n Log[x] in general. For example consider n = 2 and x = -2. Log[x^n] would evaluate to Log[4] a real number while n Log[x] evaluates to 2 Log[-2] a complex number. However you can achieve what you want using PowerExpand, i.e., In[1]:= PowerExpand[Log[x^n] - n*Log[x]] Out[1]= 0 -- To reply via email subtract one hundred and four