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():
	      _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 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.

ATTRIBUTES
       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
       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
       This page is part of release 4.10 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/.



				  2016-03-15			      ATAN2(3)