Re: Possible Bug in ArcTan ?

*To*: mathgroup at smc.vnet.net*Subject*: [mg64797] Re: [mg64770] Possible Bug in ArcTan ?*From*: Bob Hanlon <hanlonr at cox.net>*Date*: Thu, 2 Mar 2006 21:46:52 -0500 (EST)*Reply-to*: hanlonr at cox.net*Sender*: owner-wri-mathgroup at wolfram.com

Plot3D[ArcTan[y/x], {x, -1, 1}, {y, -1, 1}]; As expected, there is a discontinuity for x=0 Plot[Evaluate[Table[ArcTan[y/x], {x,-1+10^-8,1+10^-8,1/2}]],{y,-1,1}, PlotStyle->Table[Hue[(x+3)/4],{x,-1,1,1/2}], Frame->True,Axes->False]; Bob Hanlon > > From: "JCDenton" <post4uw at web.de> To: mathgroup at smc.vnet.net > Subject: [mg64797] [mg64770] Possible Bug in ArcTan ? > > Hi Group! > > I am describing resonant electrical systems with Mathematica. So there > is a lot of dealing with complex numbers and functions. One important > function is: > > phi=ArcTan[Im/Re] > > This function is zero when Im = 0. The problem is, that when I plot > this function it shows some strange behaviour near this zero point. It > looks somehow, as if the function values are multiplied with -1 or > something like that. I also tried to calculate a table an plot this > with gnuplot where the stepsize was 0.005. I was the same strange > situation. So I am sure it is not the Plot function that is buggy but > the ArcTan itself. I also tried the table with step size 0.05 and I get > the "right" picture with gnuplot. Is this a known bug? I have not found > something about it yet. > > I realy need this function, since it is a very important operation in > complex calculation. > > Thank you! > >