_BSD_SOURCE || _SVID_SOURCE || _XOPEN_SOURCE >= 500 ||
_XOPEN_SOURCE && _XOPEN_SOURCE_EXTENDED || _ISOC99_SOURCE ||
_POSIX_C_SOURCE >= 200112L;
or
cc -std=c99

atanhf(),
atanhl():

_BSD_SOURCE || _SVID_SOURCE || _XOPEN_SOURCE >= 600 || _ISOC99_SOURCE ||
_POSIX_C_SOURCE >= 200112L;
or
cc -std=c99

DESCRIPTION

The
atanh()
function calculates the inverse hyperbolic tangent of
x; that is the value whose hyperbolic tangent is x.

RETURN VALUE

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.

If
x
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.

ERRORS

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: x less than -1 or greater than +1

errno
is set to
EDOM.
An invalid floating-point exception
(FE_INVALID)
is raised.

Pole error: x is +1 or -1

errno
is set to
ERANGE
(but see BUGS).
A divide-by-zero floating-point exception
(FE_DIVBYZERO)
is raised.

CONFORMING TO

C99, POSIX.1-2001.
The variant returning
double
also conforms to
SVr4, 4.3BSD, C89.

BUGS

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.

This page is part of release 3.27 of the Linux
man-pages
project.
A description of the project,
and information about reporting bugs,
can be found at
http://www.kernel.org/doc/man-pages/.