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Re: Problem with D and Abs

• To: mathgroup at smc.vnet.net
• Subject: [mg60990] Re: Problem with D and Abs
• From: "Jens-Peer Kuska" <kuska at informatik.uni-leipzig.de>
• Date: Fri, 7 Oct 2005 03:37:37 -0400 (EDT)
• Organization: Uni Leipzig
• References: <di1m0c$2r8$1@smc.vnet.net>
• Sender: owner-wri-mathgroup at wolfram.com

Hi,

FullSimplify[expr,Element[x,Reals] && 
Element[y,Complexes]]

or

Refine[expr,Element[x,Reals] && 
Element[y,Complexes]]

or

Assuming[Element[x,Reals] && Element[y,Complexes], 
expr]

will simplify, evaluate your expression expr and 
handle x as real
and y as complex.

Regards
  Jens

"Daniele Lupo" <danwolf80_no_spam_ at libero.it> 
schrieb im Newsbeitrag 
news:di1m0c$2r8$1 at smc.vnet.net...
| Hi to all.
|
| I've a problem with this expression:
|
| \!\(Abs[\(Conjugate[s11]\ g\_s\)\/\(1 + 
Abs[s11]\^2\ \((\(-1\) + g\_s)\)\)
| - \
| Ã\_0\/\(1 + N\_i\)] - \@\(N\_i\ \((1 - 
Abs[Ã\_0]\^2 + N\_i)\)\)\/\(1 +
| N\_i\)\
| \)
|
|
| I want to have derivative in gs. If I use D, I 
obtain a strange result,
| that invoke Abs'[...], that's not correct, 
naturally.
|
| I've tried to use PiecewiseExpand, but I've a 
problem. In this expression,
| \!\(g\_s\) and \!\(N\_i\) are real, while 
\!\(Ã\_0\) and s11 are complexes.
| I don't know how to create an expansion that 
consider some symbol as real,
| and some other as complex.
|
| How can I do it?
|
| Thanks for your answers.
|
| Daniele
|
| PS I'm using version 5.1, WinXP
|