More than one post in this thread has conflated 1r_1 with 1j_1 and I wonder if everyone who is interested (which doesn't include me) is getting the right meaning out of it.
Henry Rich > > Eldon's point, and my code on arctan _1r1, were concerned with variant > defintions of arctan. Arctan is normally defined by restricting the > domain of tangent to the open interval (-1r2p1, 1r2p1), so it > always gives > an angle in the first or fourth quadrant. In many > applications, you want > the angle from the x-axis to the point (x,y), which can be in any > quadrant. This is basically arctan y%x, except it takes sign into > account. Library functions called atan2 usually do this, and > J does it > via angle (12&o.). Then arctan _1 is _1r4p1 (in the fourth quadrant), > same as the angle to (1,_1), but different from the angle to (_1,1). > > Best wishes, > > John > > > ---------------------------------------------------------------------- > For information about J forums see > http://www.jsoftware.com/forums.htm ---------------------------------------------------------------------- For information about J forums see http://www.jsoftware.com/forums.htm
