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 > >