Re: Possible Bug in ArcTan ?
- To: mathgroup at smc.vnet.net
- Subject: [mg64798] Re: Possible Bug in ArcTan ?
- From: "David W. Cantrell" <DWCantrell at sigmaxi.org>
- Date: Thu, 2 Mar 2006 21:46:53 -0500 (EST)
- References: <firstname.lastname@example.org> <email@example.com>
- Sender: owner-wri-mathgroup at wolfram.com
"Jens-Peer Kuska" <kuska at informatik.uni-leipzig.de> wrote: > Hi, > > why can ArcTan have two arguments ArcTan[x,y] As the Help Browser says, "taking into account which quadrant the point (x,y) is in." For example, suppose you want to convert -2 + I to polar form, r*E^(I*theta). One can't simply say theta = ArcTan[1/-2]. The range of the single-argument ArcTan is [-Pi/2, Pi/2], i.e., fourth and first quadrants, while our point (-2, 1) is in the third quadrant. But we can conveniently say theta = ArcTan[-2, 1]. Note: Some other languages implement the two-argument form under the name ATAN2. Furthermore, the order of the two arguments is often backwards compared to Mathematica's, that is, ATAN2(y,x). David