**acosh**

**ACOSH(3)** Linux Programmer's Manual **ACOSH(3)**
NAME
acosh, acoshf, acoshl - inverse hyperbolic cosine function
SYNOPSIS
#include <math.h>
double acosh(double x);
float acoshf(float x);
long double acoshl(long double x);
Link with -lm.
Feature Test Macro Requirements for glibc (see **feature_test_macros(7)**):
acosh():
_ISOC99_SOURCE || _POSIX_C_SOURCE >= 200112L
|| _XOPEN_SOURCE >= 500
|| /* Since glibc 2.19: */ _DEFAULT_SOURCE
|| /* Glibc versions <= 2.19: */ _BSD_SOURCE || _SVID_SOURCE
acoshf(), acoshl():
_ISOC99_SOURCE || _POSIX_C_SOURCE >= 200112L
|| /* Since glibc 2.19: */ _DEFAULT_SOURCE
|| /* Glibc versions <= 2.19: */ _BSD_SOURCE || _SVID_SOURCE
DESCRIPTION
These functions calculate the inverse hyperbolic cosine of x; that is
the value whose hyperbolic cosine is x.
RETURN VALUE
On success, these functions return the inverse hyperbolic cosine of x.
If x is a NaN, a NaN is returned.
If x is +1, +0 is returned.
If x is positive infinity, positive infinity is returned.
If x is less than 1, a domain error occurs, and the functions return a
NaN.
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 is less than 1
errno is set to EDOM. An invalid floating-point exception
(FE_INVALID) is raised.
ATTRIBUTES
For an explanation of the terms used in this section, see
**attributes(7)**.
+-----------------------------+---------------+---------+
|Interface | Attribute | Value |
+-----------------------------+---------------+---------+
|acosh(), acoshf(), acoshl() | Thread safety | MT-Safe |
+-----------------------------+---------------+---------+
CONFORMING TO
C99, POSIX.1-2001, POSIX.1-2008.
The variant returning double also conforms to SVr4, 4.3BSD.
SEE ALSO
**asinh(3)**, **atanh(3)**, **cacosh(3)**, **cosh(3)**, **sinh(3)**, **tanh(3)**
COLOPHON
This page is part of release 4.15 of the Linux man-pages project. A
description of the project, information about reporting bugs, and the
latest version of this page, can be found at
https://www.kernel.org/doc/man-pages/.
2017-09-15 **ACOSH(3)**

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