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.

SEE ALSO

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