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

```

• Prev by Date: Re: Exporting 3D plots
• Next by Date: using iFFT on a Continuous Time Transfer Function
• Previous by thread: Re: Problem with the Derivative of a Arg-function
• Next by thread: Re: Problem with the Derivative of a Arg-function