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Expression transformation

• To: mathgroup at smc.vnet.net
• Subject: [mg59268] Expression transformation
• From: mumbojumbo <mjumbo at gmail.com>
• Date: Thu, 4 Aug 2005 02:07:52 -0400 (EDT)
• Reply-to: mumbojumbo <mjumbo at gmail.com>
• Sender: owner-wri-mathgroup at wolfram.com

Dear forum,

How can I  persuade Mathematica to transform the expression
  Exp(-x)+(a+b Exp[-x])/c
to the form
(a+(b+c)Exp(-x))/c

I have tried Together[...] and Simplify, but I always get
(b + c + a*E^x)/(c*E^x)
It looks like Mathematica is silently transforming Exp[-x] to
1/Exp[x]. How can I disable this transformation?

I am asking because in applications some equivalent forms are more
equivalent than others e.g. Exp[-u/(kT)]-1 is considered a proper form,
while (1- Exp[u/(kT)])/Exp[u/(kT)] is not.
  
Thanks, Yuri.

                         mailto:mjumbo at gmail.com

• Follow-Ups:
  • Re: Expression transformation
    • From: stephen layland <layland@wolfram.com>
  • Re: Expression transformation
    • From: Andrzej Kozlowski <akoz@mimuw.edu.pl>