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

NAME
       atan, atanf, atanl - arc tangent function

SYNOPSIS
       #include 

       double atan(double x);
       float atanf(float x);
       long double atanl( long double x);

       Link with -lm.

   Feature Test Macro Requirements for glibc (see featuretestmacros(7)):

       atanf(), atanl():
           BSDSOURCE || SVIDSOURCE || XOPENSOURCE >= 600 ||
           ISOC99SOURCE || POSIXCSOURCE >= 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.

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.  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)