atan, atanf, atanl - arc tangent function
#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)):
These functions calculate the principal value of the arc tangent of
x; that is the value whose tangent is
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].
x is a NaN, a NaN is returned.
x is +0 (-0), +0 (-0) is returned.
x is positive infinity (negative infinity), +pi/2 (-pi/2) is returned.
No errors occur.
C99, POSIX.1-2001, POSIX.1-2008.
The variant returning
double also conforms to SVr4, 4.3BSD, C89.
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