# acoshl (3)

# NAME

acosh, acoshf, acoshl - inverse hyperbolic cosine function# SYNOPSIS

#include <math.h>

double acosh(doublex);float acoshf(floatx);long double acoshl(long doublex);

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

|| _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

|| /* 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)