NAME | SYNOPSIS | DESCRIPTION | RETURN VALUE | ERRORS | ATTRIBUTES | CONFORMING TO | SEE ALSO | COLOPHON

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

NAME         top

       atan, atanf, atanl - arc tangent function

SYNOPSIS         top

       #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         top

       The atan() function calculates the principal value of the arc tangent
       of x; that is the value whose tangent is x.

RETURN VALUE         top

       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         top

       No errors occur.

ATTRIBUTES         top

   Multithreading (see pthreads(7))
       The atan(), atanf(), and atanl() functions are thread-safe.

CONFORMING TO         top

       C99, POSIX.1-2001.  The variant returning double also conforms to
       SVr4, 4.3BSD, C89.

SEE ALSO         top

       acos(3), asin(3), atan2(3), carg(3), catan(3), cos(3), sin(3), tan(3)

COLOPHON         top

       This page is part of release 3.72 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
       http://www.kernel.org/doc/man-pages/.

                                 2013-10-07                          ATAN(3)