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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():
           _BSD_SOURCE || _SVID_SOURCE || _XOPEN_SOURCE >= 600 ||
           _ISOC99_SOURCE || _POSIX_C_SOURCE >= 200112L;
           or cc -std=c99
DESCRIPTION
       The atan() function calculates 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.
CONFORMING TO
       C99, POSIX.1-2001.  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 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                           ATAN(3)