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ATANH(3) | Linux Programmer's Manual | ATANH(3) |

# NAME¶

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

#include <math.h>

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

*-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

**atanhf**(), **atanhl**():

_ISOC99_SOURCE ||
_POSIX_C_SOURCE >= 200112L
|| /* 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)# COLOPHON¶

This page is part of release 5.04 of the Linux*man-pages*project. A description of the project, information about reporting bugs, and the latest version of this page, can be found at https://www.kernel.org/doc/man-pages/.

2017-09-15 |