huschi.net

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  tan-
       gent 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 infin-
       ity, +pi (-pi) is returned.
       If y is a finite value greater (less) than 0, and x is positive  infin-
       ity, +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  infin-
       ity, +3*pi/4 (-3*pi/4) is returned.
       If  y is positive infinity (negative infinity) and x is positive infin-
       ity, +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 3.53 of the Linux man-pages project.  A
       description of the project, and information about reporting  bugs,  can
       be found at http://www.kernel.org/doc/man-pages/.

                                  2010-09-20                          ATAN2(3)