**atanh**

SYNOPSIS
#include <math.h>
double atanh(double x);
float atanhf(float x);
long double atanhl(long double x);
Link with -lm.
Feature Test Macro Requirements for glibc (see **feature_test_macros(7)**):
atanh():
_BSD_SOURCE || _SVID_SOURCE || _XOPEN_SOURCE >= 500 ||
_XOPEN_SOURCE && _XOPEN_SOURCE_EXTENDED || _ISOC99_SOURCE ||
_POSIX_C_SOURCE >= 200112L;
or cc -std=c99
atanhf(), atanhl():
_BSD_SOURCE || _SVID_SOURCE || _XOPEN_SOURCE >= 600 ||
_ISOC99_SOURCE || _POSIX_C_SOURCE >= 200112L;
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, respectively, with the mathemati-
cally 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 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 float-
ing-point exception (FE_DIVBYZERO) is raised.
COLOPHON
This page is part of release 3.54 of the Linux man-pages project. A
description of the project, and information about reporting bugs, can
be found at http://www.kernel.org/doc/man-pages/.
2010-09-11 **ATANH(3)**

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