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