ATAN2(3)                  Linux Programmer's Manual                 ATAN2(3)

NAME         top

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

SYNOPSIS         top

       #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         top

       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         top

       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         top

       No errors occur.

ATTRIBUTES         top

       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         top

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

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

SEE ALSO         top

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

COLOPHON         top

       This page is part of release 4.15 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)

Pages that refer to this page: acos(3),  asin(3),  atan(3),  cos(3),  sin(3),  tan(3)

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