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Re: Possible Bug in ArcTan ?

• To: mathgroup at smc.vnet.net
• Subject: [mg64793] Re: [mg64770] Possible Bug in ArcTan ?
• From: "David Park" <djmp at earthlink.net>
• Date: Thu, 2 Mar 2006 19:28:35 -0500 (EST)
• Sender: owner-wri-mathgroup at wolfram.com

Try the two argument form of ArcTan, ArcTan[x,y].

David Park
djmp at earthlink.net
http://home.earthlink.net/~djmp/ 

From: JCDenton [mailto:post4uw at web.de]
To: mathgroup at smc.vnet.net


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!