Re: Re: Problem with the Derivative of a Arg-function

*To*: mathgroup at smc.vnet.net*Subject*: [mg48633] Re: [mg48627] Re: Problem with the Derivative of a Arg-function*From*: Andrzej Kozlowski <akoz at mimuw.edu.pl>*Date*: Wed, 9 Jun 2004 04:16:49 -0400 (EDT)*References*: <200406040849.EAA23630@smc.vnet.net> <c9sc8g$bst$1@smc.vnet.net> <200406080448.AAA28406@smc.vnet.net>*Sender*: owner-wri-mathgroup at wolfram.com

On 8 Jun 2004, at 13:48, Alex Klishko wrote: > Andrzej Kozlowski <akoz at mimuw.edu.pl> wrote in message > >> I suppose you mean -Re[x]+2*Pi*n. But of course for complex x Re[x] > Yes, of course. > >> is not differentiable (as a function of the complex variable x !) so >> Mathematica is quite right not to return -1. > > Yes, but Mathematica is not right to return another definite number. > > Yes, but only when you use N. In such cases it performs numerical differentiation. In the case of Arg it looks like a bug, as Maxim has already pointed out. Note, however that: N[D[ComplexExpand[Arg[E^((-I)*x)], {x}], x] /. x -> 1] -1.*Derivative[1][Re][1.] Andrzej

**References**:**Re: Problem with the Derivative of a Arg-function***From:*klishko@mail.ru (Alex Klishko)

**Re: Problem with the Derivative of a Arg-function***From:*klishko@mail.ru (Alex Klishko)