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 (see feature_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 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 │
       └─────────────────────────────┴───────────────┴─────────┘

CONFORMING TO

       C99, POSIX.1-2001, POSIX.1-2008.

       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)

COLOPHON

       This  page  is  part  of  release  5.10  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/.

                                                   2017-09-15                                           ATAN2(3)