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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():
           _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 4.15 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/.
                                  2017-09-15                           ATAN(3)