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MathGroup Archive 2006

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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!
> 


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