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).

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