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



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():
              _BSD_SOURCE || _SVID_SOURCE || _XOPEN_SOURCE >= 600 || _ISOC99_SOURCE ||
              _POSIX_C_SOURCE >= 200112L;
              or cc -std=c99

DESCRIPTION
       The atan2() function calculates 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 radi‐
       ans; 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.

CONFORMING TO
       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)

COLOPHON
       This page is part of release 3.74 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 http://www.kernel.org/doc/man-pages/.



                                            2010-09-20                                   ATAN2(3)