atan - Man Page

Math library (libm, -lm)

#include <math.h>

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

atanf(), atanl():

    _ISOC99_SOURCE || _POSIX_C_SOURCE >= 200112L
        || /* Since glibc 2.19: */ _DEFAULT_SOURCE
        || /* glibc <= 2.19: */ _BSD_SOURCE || _SVID_SOURCE

These functions calculate the principal value of the arc tangent of x; that is the value whose tangent is x.

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.

No errors occur.

For an explanation of the terms used in this section, see attributes(7).

C11, POSIX.1-2008.

C99, POSIX.1-2001.

The variant returning double also conforms to SVr4, 4.3BSD, C89.

acos(3), asin(3), atan2(3), carg(3), catan(3), cos(3), sin(3), tan(3)

acos(3), asin(3), atan2(3), cos(3), sin(3), tan(3), unu-1op(1).

The man pages atanf(3) and atanl(3) are aliases of atan(3).