.\" Copyright (c) 2001-2003 The Open Group, All Rights Reserved 
.TH "ATANH" P 2003 "IEEE/The Open Group" "POSIX Programmer's Manual"
.\" atanh 
.SH NAME
atanh, atanhf, atanhl \- inverse hyperbolic tangent functions
.SH SYNOPSIS
.LP
\fB#include <math.h>
.br
.sp
double atanh(double\fP \fIx\fP\fB);
.br
float atanhf(float\fP \fIx\fP\fB);
.br
long double atanhl(long double\fP \fIx\fP\fB);
.br
\fP
.SH DESCRIPTION
.LP
These functions shall compute the inverse hyperbolic tangent of their
argument \fIx\fP.
.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 inverse
hyperbolic tangent of their argument.
.LP
If \fIx\fP is \(+-1, a pole error shall occur, and \fIatanh\fP(),
\fIatanhf\fP(), and \fIatanhl\fP() shall return the
value of the macro HUGE_VAL, HUGE_VALF, and HUGE_VALL, respectively,
with the same sign as the correct value of the function.
.LP
For finite |\fIx\fP|>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 \(+-0, \fIx\fP 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.
.LP
If \fIx\fP is subnormal, a range error may occur and \fIx\fP should
be returned. 
.SH ERRORS
.LP
These functions shall fail if:
.TP 7
Domain\ Error
The \fIx\fP argument is finite and 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.
.TP 7
Pole\ Error
The \fIx\fP argument is \(+-1. 
.LP
If the integer expression (math_errhandling & MATH_ERRNO) is non-zero,
then \fIerrno\fP shall be set to [ERANGE]. If the
integer expression (math_errhandling & MATH_ERREXCEPT) is non-zero,
then the divide-by-zero floating-point exception shall be
raised.
.sp
.sp
.LP
These functions may fail if:
.TP 7
Range\ Error
The value of \fIx\fP is subnormal. 
.LP
If the integer expression (math_errhandling & MATH_ERRNO) is non-zero,
then \fIerrno\fP shall be set to [ERANGE]. If the
integer expression (math_errhandling & MATH_ERREXCEPT) is non-zero,
then the underflow 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
\fIfeclearexcept\fP() , \fIfetestexcept\fP() , \fItanh\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 .