NAME

acosh, acoshf, acoshl - inverse hyperbolic cosine function

LIBRARY

Math library (`libm`, `-lm`)

SYNOPSIS

``````#include <math.h>
double acosh(double x);
float acoshf(float x);
long double acoshl(long double x);``````

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 <= 2.19: */ _BSD_SOURCE || _SVID_SOURCE``````

acoshf(), acoshl():

``````    _ISOC99_SOURCE || _POSIX_C_SOURCE >= 200112L
|| /* Since glibc 2.19: */ _DEFAULT_SOURCE
|| /* glibc <= 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

STANDARDS

C11, POSIX.1-2008.

HISTORY

C99, POSIX.1-2001.

The variant returning `double` also conforms to SVr4, 4.3BSD.