atan2(3)                   Library Functions Manual                   atan2(3)

NAME
       atan2, atan2f, atan2l - arc tangent function of two variables

LIBRARY
       Math library (libm, -lm)

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);

   Feature Test Macro Requirements for glibc (see feature_test_macros(7)):

       atan2f(), atan2l():
           _ISOC99_SOURCE || _POSIX_C_SOURCE >= 200112L
               || /* Since glibc 2.19: */ _DEFAULT_SOURCE
               || /* glibc <= 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
       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.

ERRORS
       No errors occur.

ATTRIBUTES
       For an explanation of the terms used in this section, see
       attributes(7).

       +--------------------------------------------+---------------+---------+
       |Interface                                   | Attribute     | Value   |
       +--------------------------------------------+---------------+---------+
       |atan2 (), atan2f (), atan2l ()              | Thread safety | MT-Safe |
       +--------------------------------------------+---------------+---------+
STANDARDS
       C11, POSIX.1-2008.

HISTORY
       C99, POSIX.1-2001.

       The variant returning double also conforms to SVr4, 4.3BSD, C89.

SEE ALSO
       acos(3), asin(3), atan(3), carg(3), cos(3), sin(3), tan(3)

Linux man-pages 6.7               2023-10-31                          atan2(3)