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ATAN

Section: Linux Programmer's Manual (3)
Updated: 2017-09-15
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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.

COLOPHON

This page is part of release 4.13 of the Linux man-pages project. A description of the project, information about reporting bugs, and the latest version of this page, can be found at https://www.kernel.org/doc/man-pages/.