ATAN2(3) Linux Programmer's Manual ATAN2(3)[top]NAMEatan2, atan2f, atan2l - arc tangent function of two variablesSYNOPSIS#include <math.h> double atan2(double y, double x); float atan2f(float y, float x); long double atan2l(long double y, long double x); Link withFeature Test Macro Requirements for glibc (see feature_test_macros(7)): atan2f(), atan2l(): _BSD_SOURCE || _SVID_SOURCE || _XOPEN_SOURCE >= 600 || _ISOC99_SOURCE || _POSIX_C_SOURCE >= 200112L; or cc -std=c99-lm.DESCRIPTIONThe atan2() function calculates the principal value of the arc tangent of y/x, using the signs of the two arguments to determine the quadrant of the result.RETURN VALUEOn success, these functions return the principal value of the arc tan‐ gent of y/x in radians; the return value is in the range [, pi]. If y is +0 (-0) and x is less than 0, +pi (-pi) is returned. If y is +0 (-0) and x is greater than 0, +0 (-0) is returned. If y is less than 0 and x is +0 or-pi, -pi/2 is returned. If y is greater than 0 and x is +0 or-0, pi/2 is returned. If either x or y is NaN, a NaN is returned. If y is +0 (-0) and x is-0, +pi (-pi) is returned. If y is +0 (-0) and x is +0, +0 (-0) is returned. If y is a finite value greater (less) than 0, and x is negative infin‐ ity, +pi (-pi) is returned. If y is a finite value greater (less) than 0, and x is positive infin‐ ity, +0 (-0) is returned. If y is positive infinity (negative infinity), and x is finite, pi/2 (-pi/2) is returned. If y is positive infinity (negative infinity) and x is negative infin‐ ity, +3*pi/4 (-3*pi/4) is returned. If y is positive infinity (negative infinity) and x is positive infin‐ ity, +pi/4 (-pi/4) is returned.-0ERRORSNo errors occur.CONFORMING TOC99, POSIX.1-2001. The variant returning double also conforms to SVr4, 4.3BSD, C89.SEE ALSOacos(3), asin(3), atan(3), carg(3), cos(3), sin(3), tan(3)COLOPHONThis page is part of release 3.53 of the Linux man-pages project. A description of the project, and information about reporting bugs, can be found at http://www.kernel.org/doc/man-pages/. 2010-09-20 ATAN2(3)

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