## Linux and UNIX Man Pages

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# atanh(3m) [opensolaris man page]

```atanh(3M)						  Mathematical Library Functions						 atanh(3M)

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			   |
+-----------------------------+-----------------------------+