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ATAN(3) Linux Programmer's Manual ATAN(3)

atan, atanf, atanl - arc tangent function

#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

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).
Interface Attribute Value
atan (), atanf (), atanl () Thread safety MT-Safe

C99, POSIX.1-2001, POSIX.1-2008.

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)

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2017-09-15