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?
|