SIMPLE SOLUTIONS

# ATANH, ATANHF, ATANHL - reference manual online

Inverse hyperbolic tangent function.

Chapter
2015-04-19
```ATANH(3)                            Linux Programmer's Manual                            ATANH(3)

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);

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
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, 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.