# ATANH

NAME

SYNOPSIS

DESCRIPTION

RETURN VALUE

ERRORS

ATTRIBUTES

CONFORMING TO

BUGS

SEE ALSO

COLOPHON

## NAME

atanh, atanhf,
atanhl − inverse hyperbolic tangent function

## SYNOPSIS

**#include
<math.h>**

**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 ||
_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.

## ATTRIBUTES

For an
explanation of the terms used in this section, see
**attributes**(7).

## 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.

## SEE ALSO

**acosh**(3),
**asinh**(3), **catanh**(3), **cosh**(3),
**sinh**(3), **tanh**(3)

## COLOPHON

This page is
part of release 3.53 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/.