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c99 [flag... ]file... -lm[library... ] #include <math.h>

**double atanh**(**double ***x*);

**float atanhf**(**float ***x*);

**long double atanhl**(**long double ***x*);

These functions compute the inverse hyperbolic tangent of their argument *x*.

Upon successful completion, these functions return the inverse hyperbolic tangent of their argument.

If *x* is ±1, a pole error occurs and **atanh()**, **atanhf()**, and **atanhl()** return the value of the macro **HUGE_VAL**, **HUGE_VALF**, and **HUGE_VALL**, respectively, with
the same sign as the correct value of the function.

For finite |*x*| > 1, a domain error occurs and a NaN is returned.

If *x* is NaN, NaN is returned.

If *x* is +0, *x* is returned.

If *x* is +Inf, a domain error occurs and a NaN is returned.

For exceptional cases, **matherr**(3M) tabulates the values to be returned by **atanh()** as specified by SVID3 and XPG3.

These functions will fail if:

**Domain Error**
The *x* argument is finite and not in the range [-1,1], or is ±Inf.

If the integer expression (**math_errhandling** & **MATH_ERREXCEPT**) is non-zero, the invalid floating-point exception is raised.

The **atanh()** function sets **errno** to **EDOM** if the absolute value of *x* is greater than 1.0.

**Pole Error**
The *x* argument is ±1.

If the integer expression (math_errhandling & MATH_ERREXCEPT) is non-zero, then the divide-by-zero floating-point exception is raised.

The **atanh()** function sets **errno** to **ERANGE** if the absolute value of *x* is equal to 1.0.

An application wanting to check for exceptions should call **feclearexcept**(**FE_ALL_EXCEPT**) before calling these functions. On return, if **fetestexcept**(**FE_INVALID** | **FE_DIVBYZERO** | **FE_OVERFLOW**
| **FE_UNDERFLOW**) is non-zero, an exception has been raised. An application should either examine the return value or check the floating point exception flags to detect exceptions.

An application can also set **errno** to 0 before calling **atanh()**. On return, if **errno** is non-zero, an error has occurred. The **atanhf()** and **atanhl()** functions do not set **errno**.

See **attributes**(5) for descriptions of the following attributes:

ATTRIBUTE TYPE | ATTRIBUTE VALUE |

Interface Stability | Standard |

MT-Level | MT-Safe |

**feclearexcept**(3M), **fetestexcept**(3M), **math.h**(3HEAD), **matherr**(3M), **tanh**(3M), **attributes**(5), **standards**(5)

- NAME
- SYNOPSIS
- DESCRIPTION
- RETURN VALUES
- ERRORS
- USAGE
- ATTRIBUTES
- SEE ALSO

This document was created by man2html, using the manual pages.

Time: 02:39:33 GMT, October 02, 2010