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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 3.24 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