NAME  SYNOPSIS  DESCRIPTION  RETURN VALUE  ERRORS  CONFORMING TO  SEE ALSO  COLOPHON 

ATAN2(3) Linux Programmer's Manual ATAN2(3)
atan2, atan2f, atan2l  arc tangent function of two variables
#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 with lm. Feature 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
The 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.
On success, these functions return the principal value of the arc tangent of y/x in radians; the return value is in the range [pi, 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 0, 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 infinity, +pi (pi) is returned. If y is a finite value greater (less) than 0, and x is positive infinity, +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 infinity, +3*pi/4 (3*pi/4) is returned. If y is positive infinity (negative infinity) and x is positive infinity, +pi/4 (pi/4) is returned.
No errors occur.
C99, POSIX.12001. The variant returning double also conforms to SVr4, 4.3BSD, C89.
acos(3), asin(3), atan(3), carg(3), cos(3), sin(3), tan(3)
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20100920 ATAN2(3)
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