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



NAME
       atan, atanf, atanl - arc tangent function

SYNOPSIS
       #include <math.h>

       double atan(double x);
       float atanf(float x);
       long double atanl( long double x);

       Link with -lm.

   Feature Test Macro Requirements for glibc (see feature_test_macros(7)):

       atanf(), atanl():
	   _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 x;
       that is the value whose tangent is x.

RETURN VALUE
       On success, these functions return the principal value of the arc  tan-
       gent of x in radians; the return value is in the range [-pi/2, pi/2].

       If x is a NaN, a NaN is returned.

       If x is +0 (-0), +0 (-0) is returned.

       If  x  is  positive  infinity  (negative	 infinity),  +pi/2  (-pi/2) is
       returned.

ERRORS
       No errors occur.

ATTRIBUTES
       For  an	explanation  of	 the  terms  used   in	 this	section,   see
       attributes(7).

       +-------------------------+---------------+---------+
       |Interface		 | Attribute	 | Value   |
       +-------------------------+---------------+---------+
       |atan(), atanf(), atanl() | 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), atan2(3), carg(3), catan(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			       ATAN(3)