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.\"     from: @(#)atanh.3	5.2 (Berkeley) 5/6/91
.\" $FreeBSD: src/lib/msun/man/atanh.3,v 1.13 2005/01/28 21:14:16 ru Exp $
.\"
.Dd January 14, 2005
.Dt ATANH 3
.Os
.Sh NAME
.Nm atanh ,
.Nm atanhf
.Nd inverse hyperbolic tangent functions
.Sh LIBRARY
.Lb libm
.Sh SYNOPSIS
.In math.h
.Ft double
.Fn atanh "double x"
.Ft float
.Fn atanhf "float x"
.Sh DESCRIPTION
The
.Fn atanh
and the
.Fn atanhf
functions compute 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
and the
.Fn atanhf
functions
return the inverse hyperbolic tangent of
.Ar x
if successful.
If the argument has absolute value 1, a divide-by-zero exception
is raised and an infinity is returned.
If
.Ar |x|
> 1, an invalid exception is raised and an \*(Na is returned.
.Sh SEE ALSO
.Xr acosh 3 ,
.Xr asinh 3 ,
.Xr exp 3 ,
.Xr fenv 3 ,
.Xr math 3
.Sh HISTORY
The
.Fn atanh
function appeared in
.Bx 4.3 .