Re: Problem with D and Abs

*To*: mathgroup at smc.vnet.net*Subject*: [mg60977] Re: [mg60970] Problem with D and Abs*From*: Andrzej Kozlowski <andrzej at yhc.att.ne.jp>*Date*: Thu, 6 Oct 2005 04:08:20 -0400 (EDT)*References*: <200510050628.CAA10385@smc.vnet.net>*Reply-to*: Andrzej Kozlowski <andrzej at akikoz.net>*Sender*: owner-wri-mathgroup at wolfram.com

On 5 Oct 2005, at 15:28, Daniele Lupo wrote: > 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 > > Try D[ComplexExpand[Abs[(Conjugate[s11]*Subscript[g, s])/ ((Subscript[g, s] - 1)*Abs[s11]^2 + 1) - Subscript[Ã, 0]/(Subscript[N, i] + 1)] - Sqrt[Subscript[N, i]*(-Abs[Subscript[Ã, 0]]^2 + Subscript[N, i] + 1)]/(Subscript[N, i] + 1), {s11, Subscript[Ã, 0]}], Subscript[g, s]] Andrzej Kozlowski

**References**:**Problem with D and Abs***From:*Daniele Lupo <danwolf80_no_spam_@libero.it>