atanh(3) — Linux manual pages

Linux manual pages	Section 3: Subroutines

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);

Note

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`

	Note
	Link with `−lm`.

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 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 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 floating-point exception (FE_DIVBYZERO) is raised.

CONFORMING TO

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

BUGS

In glibc 2.9 and earlier, when a pole error occurs, errno as set to EDOM instead of the POSIX-mandated ERANGE. Since version 2.10, glibc does the right thing.

COLOPHON

This page is part of release 3.52 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/.

  Copyright 1993 David Metcalfe (davidprism.demon.co.uk)
and Copyright 2008, Linux Foundation, written by Michael Kerrisk
    <mtk.manpagesgmail.com>

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References consulted:
    Linux libc source code
    Lewine's _POSIX Programmer's Guide_ (O'Reilly & Associates, 1991)
    386BSD man pages
Modified 1993-07-24 by Rik Faith (faithcs.unc.edu)
Modified 2002-07-27 by Walter Harms
(walter.harmsinformatik.uni-oldenburg.de)