atan(3) Library Functions Manual atan(3)
NAME
atan, atanf, atanl - 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 tan-
gent 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 re-
turned.
ERRORS
No errors occur.
ATTRIBUTES
For an explanation of the terms used in this section, see at-
tributes(7).
┌────────────────────────────────────────────┬───────────────┬─────────┐
│Interface │ Attribute │ Value │
├────────────────────────────────────────────┼───────────────┼─────────┤
│atan(), atanf(), atanl() │ Thread safety │ MT-Safe │
└────────────────────────────────────────────┴───────────────┴─────────┘
STANDARDS
C99, POSIX.1-2001, POSIX.1-2008.
The variant returning double also conforms to SVr4, 4.3BSD.
SEE ALSO
acos(3), asin(3), atan2(3), carg(3), catan(3), cos(3), sin(3), tan(3)
Linux man-pages 6.03 2023-02-05 atan(3)
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