# atanh(3) — Linux manual page

```atanh(3)                Library Functions Manual                atanh(3)
```

## NAME         top

```       atanh, atanhf, atanhl - inverse hyperbolic tangent function
```

## LIBRARY         top

```       Math library (libm, -lm)
```

## SYNOPSIS         top

```       #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():
_ISOC99_SOURCE || _POSIX_C_SOURCE >= 200112L
|| _XOPEN_SOURCE >= 500
|| /* Since glibc 2.19: */ _DEFAULT_SOURCE
|| /* glibc <= 2.19: */ _BSD_SOURCE || _SVID_SOURCE

atanhf(), atanhl():
_ISOC99_SOURCE || _POSIX_C_SOURCE >= 200112L
|| /* Since glibc 2.19: */ _DEFAULT_SOURCE
|| /* glibc <= 2.19: */ _BSD_SOURCE || _SVID_SOURCE
```

## DESCRIPTION         top

```       These functions calculate the inverse hyperbolic tangent of x;
that is the value whose hyperbolic tangent is x.
```

## RETURN VALUE         top

```       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         top

```       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         top

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

┌──────────────────────────────────────┬───────────────┬─────────┐
│Interface                             │ Attribute     │ Value   │
├──────────────────────────────────────┼───────────────┼─────────┤
│atanh(), atanhf(), atanhl()           │ Thread safety │ MT-Safe │
└──────────────────────────────────────┴───────────────┴─────────┘
```

## STANDARDS         top

```       C11, POSIX.1-2008.
```

## HISTORY         top

```       C99, POSIX.1-2001.

The variant returning double also conforms to SVr4, 4.3BSD.
```

## BUGS         top

```       In glibc 2.9 and earlier, when a pole error occurs, errno is set
to EDOM instead of the POSIX-mandated ERANGE.  Since glibc 2.10,
glibc does the right thing.
```

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