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Re: Expression transformation

  • To: mathgroup at smc.vnet.net
  • Subject: [mg59308] Re: [mg59268] Expression transformation
  • From: Bob Hanlon <hanlonr at cox.net>
  • Date: Fri, 5 Aug 2005 01:21:45 -0400 (EDT)
  • Reply-to: hanlonr at cox.net
  • Sender: owner-wri-mathgroup at wolfram.com

expr=Exp[-x]+(a+b Exp[-x])/c;

Collect[expr,E^-x]

a/c + (b/c + 1)/E^x

Collect[expr//Simplify,E^-x]

a/c + (b + c)/(E^x*c)

Collect[c*expr//Simplify,E^-x]/c

(a + (b + c)/E^x)/c

expr=(1-Exp[u/(kT)])/Exp[u/(kT)];

expr//Simplify

-1 + E^(-(u/kT))


Bob Hanlon

> 
> From: mumbojumbo <mjumbo at gmail.com>
To: mathgroup at smc.vnet.net
> Date: 2005/08/04 Thu AM 02:07:52 EDT
> Subject: [mg59308] [mg59268] Expression transformation
> 
> 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
> 
> 


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