Re: Re: Possible Bug in ArcTan ?
- To: mathgroup at smc.vnet.net
- Subject: [mg64820] Re: [mg64793] Re: [mg64770] Possible Bug in ArcTan ?
- From: "Dr Andy D Kucar PEng" <andy at radio4u.com>
- Date: Sat, 4 Mar 2006 02:35:42 -0500 (EST)
- Reply-to: <andy at radio4u.com>
- Sender: owner-wri-mathgroup at wolfram.com
Subject: [mg64820] ArcTan[x,y], i.e., phase plot Some time ago, I reported similar problem, while calculating and plotting the phase of some functions involving Jacobi and Weierstrass elliptic functions I "observed" some strange chaotic noisy behavior near zero/ small values of phase David Park helped me with some graphic aspects, thanks. As yet, I have not fully solved the problem, I circumvented it However, the problem has not been with Mathematica algorithms, per se It appears, "my" graphics coprocessor does some short cuts, i.e., approximations, And this strange behavior might be OS state related Or, perhaps more precisely, graphics+CPU approximations ... Similar graphics related problems were reported somewhere else, outside Mathematica environment Sincerely Andy -----Original Message----- From: David Park [mailto:djmp at earthlink.net] To: mathgroup at smc.vnet.net Subject: [mg64820] [mg64793] Re: [mg64770] Possible Bug in ArcTan ? 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!