.\" Copyright (c) 1985, 1991, 1993
.\"	The Regents of the University of California.  All rights reserved.
.\"
.\" %sccs.include.redist.roff%
.\"
.\"     @(#)atanh.3	8.1 (Berkeley) 06/04/93
.\"
.Dd 
.Dt ATANH 3
.Os BSD 4.3
.Sh NAME
.Nm atanh
.Nd inverse hyperbolic tangent function
.Sh SYNOPSIS
.Fd #include <math.h>
.Ft double
.Fn atanh "double x"
.Sh DESCRIPTION
The
.Fn  atanh
function computes the inverse hyperbolic tangent
of the real
argument
.Ar x .
For a discussion of error due to roundoff, see
.Xr math 3 .
.Sh RETURN VALUES
The
.Fn atanh
function
returns the inverse hyperbolic tangent of
.Ar x
if successful.
On the
.Tn VAX
and
.Tn Tahoe ,
if the argument has absolute value
bigger than or equal to 1,
.Fn atanh
sets the global variable
.Va errno
to
.Er EDOM
and
a reserved operand fault is generated.
.Sh SEE ALSO
.Xr acosh 3 ,
.Xr asinh 3 ,
.Xr exp 3 ,
.Xr infnan 3
.Xr math 3 ,
.Sh HISTORY
The
.Fn atanh
function appeared in
.Bx 4.3 .