Re: Problem with the Derivative of a Arg-function

*To*: mathgroup at smc.vnet.net*Subject*: [mg48514] Re: Problem with the Derivative of a Arg-function*From*: klishko at mail.ru (Alex Klishko)*Date*: Fri, 4 Jun 2004 04:49:30 -0400 (EDT)*Sender*: owner-wri-mathgroup at wolfram.com

> On 2 Jun 2004, at 17:21, Andrzej Kozlowski wrote: > > I am not sure what you mean by "fase"? Is that just Arg[E^(-I*x)]? Are > you saying that this is -Re[x] for all complex x? Well, that certianly > is not true, even for real ones! You are right, Arg[E^(-I*x)] is equal to -x +2*Pi*n, where n is an integer number so, that -Pi<%<Pi. But I need an Arg's derivative. As 2*Pi*n is the constant so the derivative doesn't depend on it. So the derivative must be -1. By the way, f[x_] = ComplexExpand[Arg[E^(-I*x)]]; N[D[f[x], x]] /. x -> x0 gives -1, for any x0 (if you substitute instead x0 any real number)

**Follow-Ups**:**Re: Re: Problem with the Derivative of a Arg-function***From:*Andrzej Kozlowski <akoz@mimuw.edu.pl>