atan - Man Page

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).

InterfaceAttributeValue
atan(), atanf(), atanl()Thread safetyMT-Safe

Standards

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)

Referenced By

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).

2022-10-09 Linux man-pages 6.01