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MathGroup Archive 2006

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Re: Possible Bug in ArcTan ?

  • To: mathgroup at smc.vnet.net
  • Subject: [mg64791] Re: [mg64770] Possible Bug in ArcTan ?
  • From: Bruce Miller <brucem at wolfram.com>
  • Date: Thu, 2 Mar 2006 19:28:28 -0500 (EST)
  • References: <200603021148.GAA05303@smc.vnet.net>
  • Sender: owner-wri-mathgroup at wolfram.com

Mr. Denton,

My experiments did not show anything odd.  Could you post your
code (InputForm) and version number?

For example,

In[1]:=
$VersionNumber

Out[1]=
5.2

In[7]:=
dat = Table[{x,ArcTan[x]},{x,-2/100,2/100,0.005}];
ListPlot[dat];


Bruce Miller
Technical Support
Wolfram Research, Inc.
support at wolfram.com
http://support.wolfram.com/



On Mar 2, 2006, at 5:48 AM, 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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