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(): _BSD_SOURCE || _SVID_SOURCE || _XOPEN_SOURCE >= 600 || _ISOC99_SOURCE; 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 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.

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 3.25 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/.



                                                           2008-12-02                                                    ATAN(3)