NAME

       acosh, acoshf, acoshl - inverse hyperbolic cosine functions

SYNOPSIS

       #include <math.h>

       double acosh(double x);
       float acoshf(float x);
       long double acoshl(long double x);

DESCRIPTION

       These functions shall compute the inverse hyperbolic cosine of their argument x.

       An   application   wishing   to   check   for  error  situations  should  set  errno  to  zero  and  call
       feclearexcept(FE_ALL_EXCEPT) before calling  these  functions.   On  return,  if  errno  is  non-zero  or
       fetestexcept(FE_INVALID | FE_DIVBYZERO | FE_OVERFLOW | FE_UNDERFLOW) is non-zero, an error has occurred.

RETURN VALUE

       Upon successful completion, these functions shall return the inverse hyperbolic cosine of their argument.

       For  finite  values  of  x  <  1,  a  domain error shall occur, and  either a NaN (if supported), or   an
       implementation-defined value shall be returned.

       If x is NaN, a NaN shall be returned.

       If x is +1, +0 shall be returned.

       If x is +Inf, +Inf shall be returned.

       If x is -Inf, a domain error shall occur, and either a NaN (if supported), or  an  implementation-defined
       value shall be returned.

ERRORS

       These functions shall fail if:

       Domain Error
              The x argument is finite and less than +1.0,    or is -Inf.

       If the integer expression (math_errhandling & MATH_ERRNO) is non-zero, then errno shall be set to [EDOM].
       If  the  integer  expression  (math_errhandling & MATH_ERREXCEPT) is non-zero, then the invalid floating-
       point exception shall be raised.

       The following sections are informative.

EXAMPLES

       None.

APPLICATION USAGE

       On error, the expressions (math_errhandling & MATH_ERRNO) and  (math_errhandling  &  MATH_ERREXCEPT)  are
       independent of each other, but at least one of them must be non-zero.

RATIONALE

       None.

FUTURE DIRECTIONS

       None.

SEE ALSO

       cosh()  , feclearexcept() , fetestexcept() , the Base Definitions volume of IEEE Std 1003.1-2001, Section
       4.18, Treatment of Error Conditions for Mathematical Functions, <math.h>

COPYRIGHT

       Portions of this text are reprinted and reproduced in electronic form from IEEE Std 1003.1, 2003 Edition,
       Standard for Information Technology -- Portable Operating System Interface (POSIX), The Open  Group  Base
       Specifications Issue 6, Copyright (C) 2001-2003 by the Institute of Electrical and Electronics Engineers,
       Inc  and  The  Open Group. In the event of any discrepancy between this version and the original IEEE and
       The Open Group Standard, the original IEEE and The Open Group  Standard  is  the  referee  document.  The
       original Standard can be obtained online at http://www.opengroup.org/unix/online.html .

IEEE/The Open Group                                   2003                                              ACOSH(P)