Re: Cannot plot this functions

*To*: mathgroup at smc.vnet.net*Subject*: [mg53852] Re: [mg53830] Cannot plot this functions*From*: Bob Hanlon <hanlonr at cox.net>*Date*: Sun, 30 Jan 2005 03:18:13 -0500 (EST)*Reply-to*: hanlonr at cox.net*Sender*: owner-wri-mathgroup at wolfram.com

f[x_] := -ArcTan[(-Sqrt[2])*Im[x] - Re[x^2] + 1, Sqrt[2]*Re[x] - Im[x^2]]; -f'[x]//Simplify -(((Sqrt[2]*Im[x] + Re[x^2] - 1)*(Sqrt[2]*Derivative[1][Re][x] - 2*x*Derivative[1][Im][x^2]) + (Im[x^2] - Sqrt[2]*Re[x])*(Sqrt[2]*Derivative[1][Im][x] + 2*x*Derivative[1][Re][x^2]))/ ((Im[x^2] - Sqrt[2]*Re[x])^2 + (Sqrt[2]*Im[x] + Re[x^2] - 1)^2)) The problem is the terms with the derivative of Re or Im. However, if you are plotting for real x g[x_] = Simplify[f[x],Element[x, Reals]]; g[x] -ArcTan[1 - x^2, Sqrt[2]*x] -g'[x]//Simplify (Sqrt[2]*(x^2 + 1))/(x^4 + 1) Plot[{f[x],-g'[x]}, {x,-10,10}, PlotStyle->{Blue,Red}, ImageSize->400]; Bob Hanlon > > From: Milind Gupta <milind.gupta at gmail.com> To: mathgroup at smc.vnet.net > Date: 2005/01/29 Sat AM 06:02:38 EST > To: mathgroup at smc.vnet.net > Subject: [mg53852] [mg53830] Cannot plot this functions > > Hello, > I have a function of a phase response like: > > -ArcTan[1 - sqrt(2)* Im[Ï?] - Re[Ï?^2], -Im[Ï?^2] + sqrt(2)* Re[Ï?]] > > I need to plot the negative derivative of this function with respect > to Ï?. Whne I use plot it gives me the error: > > function is not a machine - size real number at Ï? =1.8622242690864824`*^-7 > > How can I avoid this problem?? > > Milind > >