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():
           _ISOC99_SOURCE || _POSIX_C_SOURCE >= 200112L
               || /* Since glibc 2.19: */ _DEFAULT_SOURCE
               || /* Glibc versions <= 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 │
       └──────────────────────────┴───────────────┴─────────┘

CONFORMING TO

       C99, POSIX.1-2001, POSIX.1-2008.

       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

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                                                   2017-09-15                                            ATAN(3)