atan(3) — Linux manual page

atan(3)                  Library Functions Manual                 atan(3)

NAME         top

       atan, atanf, atanl - arc tangent function

LIBRARY         top

       Math library (libm, -lm)

SYNOPSIS         top

       #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         top

       These functions calculate 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

       For an explanation of the terms used in this section, see
       attributes(7).
       ┌──────────────────────────────────────┬───────────────┬─────────┐
       │ Interface                            │ Attribute     │ Value   │
       ├──────────────────────────────────────┼───────────────┼─────────┤
       │ atan(), atanf(), atanl()             │ Thread safety │ MT-Safe │
       └──────────────────────────────────────┴───────────────┴─────────┘

STANDARDS         top

       C11, POSIX.1-2008.

HISTORY         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

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Linux man-pages 6.15            2025-05-17                        atan(3)

Pages that refer to this page: acos(3),  asin(3),  atan2(3),  cos(3),  sin(3),  tan(3)

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