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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).

       ┌─────────────────────────────┬───────────────┬─────────┐
       │InterfaceAttributeValue   │
       ├─────────────────────────────┼───────────────┼─────────┤
       │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

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                                  2016-03-15                          ATAN2(3)