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ATAN2(3) Linux Programmer's Manual ATAN2(3)NAMEatan2, atan2f, atan2l - arc tangent function of two variablesSYNOPSIS#include<math.h>doubleatan2(doubley,doublex);floatatan2f(floaty,floatx);longdoubleatan2l(longdoubley,longdoublex);Link with-lm. Feature Test Macro Requirements for glibc (see feature_test_macros(7)):atan2f(),atan2l(): _BSD_SOURCE || _SVID_SOURCE || _XOPEN_SOURCE >= 600 || _ISOC99_SOURCE; orcc-std=c99DESCRIPTIONTheatan2() function calculates the principal value of the arc tangent ofy/x, using the signs of the two argu- ments to determine the quadrant of the result.RETURNVALUEOn success, these functions return the principal value of the arc tangent ofy/xin radians; the return value is in the range [-pi, pi]. Ifyis +0 (-0) andxis less than 0, +pi (-pi) is returned. Ifyis +0 (-0) andxis greater than 0, +0 (-0) is returned. Ifyis less than 0 andxis +0 or -0, -pi/2 is returned. Ifyis greater than 0 andxis +0 or -0, pi/2 is returned. If eitherxoryis NaN, a NaN is returned. Ifyis +0 (-0) andxis -0, +pi (-pi) is returned. Ifyis +0 (-0) andxis +0, +0 (-0) is returned. Ifyis a finite value greater (less) than 0, andxis negative infinity, +pi (-pi) is returned. Ifyis a finite value greater (less) than 0, andxis positive infinity, +0 (-0) is returned. Ifyis positive infinity (negative infinity), andxis finite, pi/2 (-pi/2) is returned. Ifyis positive infinity (negative infinity) andxis negative infinity, +3*pi/4 (-3*pi/4) is returned. Ifyis positive infinity (negative infinity) andxis positive infinity, +pi/4 (-pi/4) is returned.ERRORSNo errors occur.CONFORMINGTOC99, POSIX.1-2001. The variant returningdoublealso conforms to SVr4, 4.3BSD, C89.SEEALSOacos(3), asin(3), atan(3), carg(3), cos(3), sin(3), tan(3)COLOPHONThis page is part of release 3.22 of the Linuxman-pagesproject. A description of the project, and informa- tion about reporting bugs, can be found at http://www.kernel.org/doc/man-pages/. 2008-11-20 ATAN2(3)