Linux Programmer’s Manual
atanh, atanhf, atanhl − inverse hyperbolic tangent function
double atanh(double x);
float atanhf(float x);
long double atanhl(long double x);
Link with −lm.
Feature Test Macro Requirements for glibc (see feature_test_macros(7)):
atanh(): _BSD_SOURCE || _SVID_SOURCE || _XOPEN_SOURCE >= 500 || _ISOC99_SOURCE; or
atanhf(), atanhl(): _BSD_SOURCE || _SVID_SOURCE || _XOPEN_SOURCE >= 600 ||
_ISOC99_SOURCE; or cc -std=c99
The atanh() function calculates the inverse hyperbolic tangent of x; that is the value whose hyperbolic tan-
gent is x.
On success, these functions return the inverse hyperbolic tangent of x.
If x is a NaN, a NaN is returned.
If x is +0 (−0), +0 (−0) is returned.
is +1 or −1, a pole error occurs, and the functions return HUGE_VAL, HUGE_VALF, or
HUGE_VALL, respectively, with the mathematically correct sign.
If the absolute value of x is greater than 1, a domain error occurs, and a NaN is returned.
See math_error(7) for information on how to determine whether an error has occurred when calling these
The following errors can occur:
Domain error: x less than −1 or greater than +1
errno is set to EDOM. An inv alid floating-point exception (FE_INVALID) is raised.
Pole error: x is +1 or −1
is set to ERANGE (but see BUGS). A divide-by-zero floating-point exception
(FE_DIVBYZERO) is raised.
C99, POSIX.1-2001. The variant returning double also conforms to SVr4, 4.3BSD, C89.
For a pole error, errno is set to EDOM; POSIX.1 says it should be set to ERANGE.
acosh(3), asinh(3), catanh(3), cosh(3), sinh(3), tanh(3)
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