.\" Copyright (c) 2001-2003 The Open Group, All Rights Reserved 
.TH "ACOS" P 2003 "IEEE/The Open Group" "POSIX Programmer's Manual"
.\" acos 
.SH NAME
acos, acosf, acosl \- arc cosine functions
.SH SYNOPSIS
.LP
\fB#include <math.h>
.br
.sp
double acos(double\fP \fIx\fP\fB);
.br
float acosf(float\fP \fIx\fP\fB);
.br
long double acosl(long double\fP \fIx\fP\fB);
.br
\fP
.SH DESCRIPTION
.LP
These functions shall compute the principal value of the arc cosine
of their argument \fIx\fP. The value of \fIx\fP should be
in the range [-1,1].
.LP
An application wishing to check for error situations should set \fIerrno\fP
to zero and call
\fIfeclearexcept\fP(FE_ALL_EXCEPT) before calling these functions.
On return, if \fIerrno\fP is non-zero or
\fIfetestexcept\fP(FE_INVALID | FE_DIVBYZERO | FE_OVERFLOW | FE_UNDERFLOW)
is non-zero, an error has occurred.
.SH RETURN VALUE
.LP
Upon successful completion, these functions shall return the arc cosine
of \fIx\fP, in the range [0,pi] radians.
.LP
For finite values of \fIx\fP not in the range [-1,1], a domain error
shall occur, and   \ either a NaN
(if supported), or  \ an implementation-defined value shall be
returned.
.LP
If
\fIx\fP is NaN, a NaN shall be returned.
.LP
If \fIx\fP is +1, +0 shall be returned.
.LP
If \fIx\fP is \(+-Inf, a domain error shall occur, and either a NaN
(if supported), or an implementation-defined value
shall be returned. 
.SH ERRORS
.LP
These functions shall fail if:
.TP 7
Domain\ Error
The \fIx\fP argument is finite and is not in the range [-1,1],   \ or
is \(+-Inf.  
.LP
If the integer expression (math_errhandling & MATH_ERRNO) is non-zero,
then \fIerrno\fP 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.
.sp
.LP
\fIThe following sections are informative.\fP
.SH EXAMPLES
.LP
None.
.SH APPLICATION USAGE
.LP
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.
.SH RATIONALE
.LP
None.
.SH FUTURE DIRECTIONS
.LP
None.
.SH SEE ALSO
.LP
\fIcos\fP() , \fIfeclearexcept\fP() , \fIfetestexcept\fP() , \fIisnan\fP()
, the Base Definitions volume of
IEEE\ Std\ 1003.1-2001, Section 4.18, Treatment of Error Conditions
for
Mathematical Functions, \fI<math.h>\fP
.SH 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 .