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 |