Clément Calenge <[EMAIL PROTECTED]> writes: > Dear all, > > I've got a problem with the function atan2. For a couple of > coordinates x and y, > This function returns the angle between the vector of coordinates (x, > y) and the > abscissa axis, i.e. it is the same as atan(y/x) (as indicated on the > help page). > If we consider the vector with coordinates x = 0 and y = 0, we have > the following result: > > > atan(0/0) > [1] NaN > > This is expected. However: > > > atan2(0,0) > [1] 0 > > Instead of a missing value, the function atan2 returns an angle equal > to 0 radians. > I've searched through the help pages, the FAQ and the forum, but I > did'nt find > any explanation to this result. Does anyone know if this behavior is > expected, and > why ? > Thank you for any clues.
Yes, it is expected. R just copies what the C library function does, but there is actually a rationale: http://www-sbras.nsc.ru/cgi-bin/www/unix_help/unix-man?atan2+3 Briefly: You don't get a natural conversion to spherical coordinates and back without this convention. -- O__ ---- Peter Dalgaard Blegdamsvej 3 c/ /'_ --- Dept. of Biostatistics 2200 Cph. N (*) \(*) -- University of Copenhagen Denmark Ph: (+45) 35327918 ~~~~~~~~~~ - ([EMAIL PROTECTED]) FAX: (+45) 35327907 ______________________________________________ R-help@stat.math.ethz.ch mailing list https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide! http://www.R-project.org/posting-guide.html
