For land surveying calculations, I usually need both distance and angle (or direction), so I use something like:
NB. ============================================ 'd a'=. *. 147.23j523.78 NB. real part is delta north and imaginary part is delta east NB. then 2p1|a is azimuth (clockwise angle from north) in radians d 544.079 a 1.29678 NB. ============================================ -----Original Message----- From: [email protected] [mailto:[email protected]] On Behalf Of Don Kelly Sent: Wednesday, March 12, 2014 20:17 To: [email protected] Subject: Re: [Jprogramming] atan2 ? My typo -----correction 12&0. not 13&o. I agree with Bill Lam as typically one isn't making a table but finding an angle from a given complex number (or array) 12&0. @j./~ makes a table Don Using 13&o. as Tom suggested: at=:13&o. at j./~i:100 gives the same result with both viewmat and plot as atan2"0/~ i:100 Don On 11/03/2014 4:59 PM, Raul Miller wrote: > This might be what you are looking for? > atan2trivial=: _3 o. %~ > atan2=: 0 { [: +. [: r.^:_1 j. > > For the principal domain, atan2trivial matches atan2 > 1 (atan2trivial -: atan2) 2 > 1 > > However, atan2 can distinguish direction when x=0 > 0 atan2 1 > 1.5708 > 0 atan2 _1 > _1.5708 > > I'd like more test cases, though. I've not been doing much trig > recently, and it's possible I made a mistake. > > Maybe someone who has been working with this kind of math can judge > from what viewmat displays? > > require 'viewmat' > viewmat atan2"0/~ i:100 > > Thanks, > ---------------------------------------------------------------------- For information about J forums see http://www.jsoftware.com/forums.htm ---------------------------------------------------------------------- For information about J forums see http://www.jsoftware.com/forums.htm
