ATAN

NAME
SYNOPSIS
DESCRIPTION
RETURN VALUE
ERRORS
ATTRIBUTES
CONFORMING TO
SEE ALSO
COLOPHON

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():

_BSD_SOURCE || _SVID_SOURCE || _XOPEN_SOURCE >= 600 || _ISOC99_SOURCE || _POSIX_C_SOURCE >= 200112L;
or cc -std=c99

DESCRIPTION

The atan() function calculates 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).

Image grohtml-17701.png

CONFORMING TO

C99, POSIX.1-2001. 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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