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Re: Real/Comlex function problem with D

• To: mathgroup at smc.vnet.net
• Subject: [mg74244] Re: Real/Comlex function problem with D
• From: "Michael Weyrauch" <michael.weyrauch at gmx.de>
• Date: Thu, 15 Mar 2007 05:04:30 -0500 (EST)
• References: <et8e29$pqb$1@smc.vnet.net>

Hello,

  because it's correct. It's complex! Just use the chain rule to proof it.
You probably want to compute

Arg[D[ff[x],x]]  ???

Michael Weyrauch


<bar at ANTYSPAM.ap.krakow.pl> schrieb im Newsbeitrag news:et8e29$pqb$1 at smc.vnet.net...
> Hi,
> I have a complex function F[x]
> When i defined:
> ff[x_]:=Arg[F[x]]   (* i tried ComplexExpand[Arg[F[x]]] too *)
> 
> I obtainned good Plot[ff[x]] - its real - (no complex)
> 
> When i try 
> ff1[x_]:=D[ff[x],x];
> I found ff1 is Complex funtion again !!
> 
> Why ?
> 
> (i tried Evaluate; Element[x,Reals]; FullSimplify - always the same)
> 
> Regards, Olaf
> 
>