# atanhl (3)

# NAME

atanh, atanhf, atanhl - inverse hyperbolic tangent function# SYNOPSIS

#include <math.h>

double atanh(doublex);float atanhf(floatx);long double atanhl(long doublex);

Link with

*-lm*.

Feature Test Macro Requirements for glibc (see

**feature_test_macros**(7)):

**atanh**():

_ISOC99_SOURCE || _POSIX_C_SOURCE >= 200112L

|| _XOPEN_SOURCE >= 500

|| /* Since glibc 2.19: */ _DEFAULT_SOURCE

|| /* Glibc versions <= 2.19: */ _BSD_SOURCE || _SVID_SOURCE

|| _XOPEN_SOURCE >= 500

|| /* Since glibc 2.19: */ _DEFAULT_SOURCE

|| /* Glibc versions <= 2.19: */ _BSD_SOURCE || _SVID_SOURCE

**atanhf**(),

**atanhl**():

_ISOC99_SOURCE || _POSIX_C_SOURCE >= 200112L

|| /* Since glibc 2.19: */ _DEFAULT_SOURCE

|| /* Glibc versions <= 2.19: */ _BSD_SOURCE || _SVID_SOURCE

|| /* Since glibc 2.19: */ _DEFAULT_SOURCE

|| /* Glibc versions <= 2.19: */ _BSD_SOURCE || _SVID_SOURCE

# DESCRIPTION

These functions calculate 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).

Interface | Attribute | Value |

atanh (), atanhf (), atanhl () | Thread safety | MT-Safe |

# CONFORMING TO

C99, POSIX.1-2001, POSIX.1-2008. The variant returning*double*also conforms to SVr4, 4.3BSD.

# 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)