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MathGroup Archive 2000

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Re: Why doesn't Log[ E^x ] = x ?

  • To: mathgroup at smc.vnet.net
  • Subject: [mg24434] Re: Why doesn't Log[ E^x ] = x ?
  • From: Paul Abbott <paul at physics.uwa.edu.au>
  • Date: Tue, 18 Jul 2000 00:58:32 -0400 (EDT)
  • Organization: University of Western Australia
  • References: <8jrdc2$e2t@smc.vnet.net> <8k0tnp$q40@smc.vnet.net>
  • Sender: owner-wri-mathgroup at wolfram.com

In article <8k0tnp$q40 at smc.vnet.net>, "Bill Bertram" <wkb at ansto.gov.au> 
wrote:

> Christopher R. Carlen <crcarle at sandia.gov> wrote in message
> news:8jrdc2$e2t at smc.vnet.net...
> > Hi:
> >
> > E^Log[x] evaluates to x
> >
> > but
> >
> > Log[ E^x ] evaluates to Log[ E^x ]
> >
> > Why?
> >
> 
> 
> Same for Mathematica Version 4, except if you use "PowerExpand".
> 
>      PowerExpand[Log[Exp[x]]]  -> x

A better (safer) solution is to use

   Simplify[Log[E^x], Element[x, Reals]]

Cheers,
   Paul

-- 
Paul Abbott                                   Phone: +61-8-9380-2734
Department of Physics                           Fax: +61-8-9380-1014
The University of Western Australia                
Nedlands WA  6907                      
AUSTRALIA                             http://physics.uwa.edu.au/~paul


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