Content-type: text/html Man page of atanh

# atanh

Section: Mathematical Library Functions (3M)
Updated: 12 Jul 2006

## NAME

atanh, atanhf, atanhl - inverse hyperbolic tangent functions

## SYNOPSIS

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

double atanh(double x);

float atanhf(float x);

long double atanhl(long double x);

## DESCRIPTION

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

## RETURN VALUES

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.

## ERRORS

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.

## USAGE

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.

## ATTRIBUTES

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