ATAN2(3)Linux Programmer's ManualATAN2(3)NAME atan2, atan2f, atan2l - arc tangent function of two variables SYNOPSIS #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 (seefeature_test_macros(7)): atan2f(), atan2l(): _ISOC99_SOURCE || _POSIX_C_SOURCE >= 200112L || /* Since glibc 2.19: */ _DEFAULT_SOURCE || /* Glibc versions <= 2.19: */ _BSD_SOURCE || _SVID_SOURCE DESCRIPTION These functions calculate 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 VALUE On 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, 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 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. ERRORS No errors occur. ATTRIBUTES For an explanation of the terms used in this section, see at-tributes(7). +-----------------------------+---------------+---------+ |Interface | Attribute | Value | +-----------------------------+---------------+---------+ |atan2(), atan2f(), atan2l() | Thread safety | MT-Safe | +-----------------------------+---------------+---------+ CONFORMING TO C99, POSIX.1-2001, POSIX.1-2008. 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)COLOPHON This page is part of release 5.05 of the Linux man-pages project. A description of the project, information about reporting bugs, and the latest version of this page, can be found at https://www.kernel.org/doc/man-pages/. 2017-09-15ATAN2(3)