Section (3) atanh
atanh, atanhf, atanhl — inverse hyperbolic tangent function
||long double x
These functions calculate the inverse hyperbolic tangent
x; that is the
value whose hyperbolic tangent is
On success, these functions return the inverse hyperbolic
x is a NaN, a
NaN is returned.
x is +0
(−0), +0 (−0) is returned.
x is +1 or
−1, a pole error occurs, and the functions return
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 functions.
The following errors can occur:
- Domain error:
xless than −1 or greater than +1
errnois set to EDOM. An invalid floating-point exception (
FE_INVALID) is raised.
- Pole error:
xis +1 or −1
errnois set to ERANGE (but see BUGS). A divide-by-zero floating-point exception (
FE_DIVBYZERO) is raised.
For an explanation of the terms used in this section, see attributes(7).
C99, POSIX.1-2001, POSIX.1-2008.
The variant returning double also conforms to SVr4, 4.3BSD.
In glibc 2.9 and earlier, when a pole error occurs,
errno as set to EDOM instead of the POSIX-mandated
ERANGE. Since version 2.10,
glibc does the right thing.
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Linux libc source code
Lewine_zsingle_quotesz_s _POSIX Programmer_zsingle_quotesz_s Guide_ (O_zsingle_quotesz_Reilly & Associates, 1991)
386BSD man pages
Modified 1993-07-24 by Rik Faith (faithcs.unc.edu)
Modified 2002-07-27 by Walter Harms