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).

       allbox;  lbw24  lb  lb  l  l  l.   Interface Attribute Value T{ atan(),
       atanf(), atanl() T}   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 4.16 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)