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Re: transforming exponential of sums into product of exponentials

• To: mathgroup at smc.vnet.net
• Subject: [mg48670] Re: transforming exponential of sums into product of exponentials
• From: Jens-Peer Kuska <kuska at informatik.uni-leipzig.de>
• Date: Thu, 10 Jun 2004 02:43:05 -0400 (EDT)
• Organization: Universitaet Leipzig
• References: <ca6igm$j2s$1@smc.vnet.net>
• Reply-to: kuska at informatik.uni-leipzig.de
• Sender: owner-wri-mathgroup at wolfram.com

Hi,

it does it because it also evaluate 2*2 to 4.
You must use a Hold[] to prevent the simplifications

Exp[x + y] /. Exp[a_ + b_] :>  Hold[Exp[a]Exp[b]] 

Regards
  Jens

Karim Mehadhebi wrote:
> 
> Dear All,
> 
> I can not understand why Mathmatica refuses to apply rules which transform
> exponenials of sums into product of exponentails.
> 
> For instance,
> f[x+y] /. f[a_ + b_]-> f[a] f[b] returns f[x] f[y],
> whereas
> Exp[x+y] /. Exp[a_+b_]->Exp[a]Exp[b] still returns Exp[x+y]
> 
> Any help greatly appreciated