acosh(3) — Linux manual page

```acosh(3)                Library Functions Manual                acosh(3)
```

NAME         top

```       acosh, acoshf, acoshl - inverse hyperbolic cosine function
```

LIBRARY         top

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

SYNOPSIS         top

```       #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         top

```       These functions calculate the inverse hyperbolic cosine of x;
that is the value whose hyperbolic cosine is x.
```

RETURN VALUE         top

```       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         top

```       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         top

```       For an explanation of the terms used in this section, see
attributes(7).
┌─────────────────────────────────────┬───────────────┬─────────┐
│ Interface                           │ Attribute     │ Value   │
├─────────────────────────────────────┼───────────────┼─────────┤
│ acosh(), acoshf(), acoshl()         │ Thread safety │ MT-Safe │
└─────────────────────────────────────┴───────────────┴─────────┘
```

STANDARDS         top

```       C11, POSIX.1-2008.
```

HISTORY         top

```       C99, POSIX.1-2001.

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

```       asinh(3), atanh(3), cacosh(3), cosh(3), sinh(3), tanh(3)