# Man Pages

atanh(3) - phpMan atanh(3) - phpMan

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```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 || _ISOC99_SOURCE; or cc -std=c99
atanhf(), atanhl(): _BSD_SOURCE || _SVID_SOURCE || _XOPEN_SOURCE >= 600 || _ISOC99_SOURCE; or cc -std=c99

DESCRIPTION
The atanh() function calculates 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,  respec-
tively, 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 func-
tions.

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.  A divide-by-zero floating-point exception (FE_DIVBYZERO) is raised.

CONFORMING TO
C99, POSIX.1-2001.  The variant returning double also conforms to SVr4, 4.3BSD, C89.