'\" te
.\" Copyright (c) 2001, the Institute of Electrical and Electronics Engineers, Inc. and The Open Group. All Rights Reserved.
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.TH acosh 3M "12 Jul 2006" "SunOS 5.11" "Mathematical Library Functions"
.SH NAME
acosh, acoshf, acoshl \- inverse hyperbolic cosine functions
.SH SYNOPSIS
.LP
.nf
c99 [ \fIflag\fR... ] \fIfile\fR... \fB-lm\fR [ \fIlibrary\fR... ]
#include <math.h>

\fBdouble\fR \fBacosh\fR(\fBdouble\fR \fIx\fR);
.fi

.LP
.nf
\fBfloat\fR \fBacoshf\fR(\fBfloat\fR \fIx\fR);
.fi

.LP
.nf
\fBlong double\fR \fBacoshl\fR(\fBlong double\fR \fIx\fR);
.fi

.SH DESCRIPTION
.sp
.LP
These functions compute the inverse hyperbolic cosine of their argument
\fIx\fR.
.SH RETURN VALUES
.sp
.LP
Upon successful completion, these functions return the inverse hyperbolic
cosine of their argument.
.sp
.LP
For finite values of  \fIx\fR < 1, a domain error occurs and NaN is returned.
.sp
.LP
If \fIx\fR is NaN, NaN is returned.
.sp
.LP
If \fIx\fR is +1, +0 is returned.
.sp
.LP
If \fIx\fR is +Inf, +Inf is returned.
.sp
.LP
If \fIx\fR is \(miInf, a domain error occurs and NaN is returned.
.sp
.LP
For exceptional cases, \fBmatherr\fR(3M) tabulates the values to be returned by
\fBacosh()\fR as specified by SVID3 and XPG3.
.SH ERRORS
.sp
.LP
These functions will fail if:
.sp
.ne 2
.mk
.na
\fBDomain Error\fR
.ad
.RS 16n
.rt  
The \fIx\fR argument is finite and less than 1.0, or is \(miInf.
.sp
If the integer expression (\fBmath_errhandling\fR & \fBMATH_ERREXCEPT\fR) is
non-zero, the invalid floating-point exception is raised.
.sp
The \fBacosh()\fR function sets \fBerrno\fR to \fBEDOM\fR if \fIx\fR is less
than 1.0.
.RE

.SH USAGE
.sp
.LP
An application wanting to check for exceptions should call
\fBfeclearexcept\fR(\fBFE_ALL_EXCEPT\fR) before calling these functions. On
return, if \fBfetestexcept\fR(\fBFE_INVALID\fR | \fBFE_DIVBYZERO\fR |
\fBFE_OVERFLOW\fR | \fBFE_UNDERFLOW\fR) is non-zero, an exception has been
raised. An application should either examine the return value or check the
floating point exception flags to detect exceptions.
.sp
.LP
An application can also set \fBerrno\fR to 0 before calling \fBacosh()\fR. On
return, if \fBerrno\fR is non-zero, an error has occurred. The \fBacoshf()\fR
and \fBacoshl()\fR functions do not set \fBerrno\fR.
.SH ATTRIBUTES
.sp
.LP
See \fBattributes\fR(5) for descriptions of the following attributes:
.sp

.sp
.TS
tab() box;
cw(2.75i) |cw(2.75i) 
lw(2.75i) |lw(2.75i) 
.
ATTRIBUTE TYPEATTRIBUTE VALUE
_
Interface StabilityStandard
_
MT-LevelMT-Safe
.TE

.SH SEE ALSO
.sp
.LP
\fBcosh\fR(3M), \fBfeclearexcept\fR(3M), \fBfetestexcept\fR(3M),
\fBmath.h\fR(3HEAD), \fBmatherr\fR(3M), \fBattributes\fR(5), \fBstandards\fR(5)