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)