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; 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.

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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