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
   tangent   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 4.09 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)

---

Free and Open Source Software