Re: Possible Bug in ArcTan ?

*To*: mathgroup at smc.vnet.net*Subject*: [mg64792] Re: Possible Bug in ArcTan ?*From*: dh <dh at metrohm.ch>*Date*: Thu, 2 Mar 2006 19:28:32 -0500 (EST)*References*: <du6o44$5rg$1@smc.vnet.net>*Sender*: owner-wri-mathgroup at wolfram.com

Hi, $Version: 5.1 for Microsoft Windows (October 25, 2004) I can not see any bug: Plot[ArcTan[x], {x, -10^-9, 10^-9}] works just fine, giving approximately just x. Could it be that there is something fishy with your denominator Re. Give an example. Daniel JCDenton wrote: > 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! >