atan(3)                    Library Functions Manual                    atan(3)

NAME
       atan, atanf, atanl - arc tangent function

LIBRARY
       Math library (libm, -lm)

SYNOPSIS
       #include <math.h>

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

   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 <= 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 |
       +--------------------------------------------+---------------+---------+
STANDARDS
       C11, POSIX.1-2008.

HISTORY
       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)

Linux man-pages 6.7               2023-10-31                           atan(3)