atan2

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; 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
       be found at http://www.kernel.org/doc/man-pages/.



                                  2008-11-20                          ATAN2(3)