.\" Copyright (c) 1985, 1991 Regents of the University of California.
.\" All rights reserved.
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.\"	This product includes software developed by the University of
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.\"    may be used to endorse or promote products derived from this software
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.\"     from: @(#)atanh.3	5.2 (Berkeley) 5/6/91
.\" %FreeBSD: src/lib/msun/man/atanh.3,v 1.6.2.3 2001/12/17 10:08:36 ru Exp %
.\"
.\" $FreeBSD$
.Dd May 6, 1991
.Dt ATANH 3
.Os
.Sh 名称
.Nm atanh ,
.Nm atanhf
.Nd 逆双曲正接関数
.Sh ライブラリ
.Lb libm
.Sh 書式
.In math.h
.Ft double
.Fn atanh "double x"
.Ft float
.Fn atanhf "float x"
.Sh 解説
.Fn  atanh
および
.Fn  atanhf
関数は、実数の引数
.Ar x
の逆双曲正接を計算します。
丸めによる誤差の議論は、
.Xr math 3
を参照してください。
.Sh 戻り値
.Fn atanh
および
.Fn atanhf
関数は、成功した場合には
.Ar x
の逆双曲正接を返します。
.Tn VAX  
および
.Tn Tahoe
では、引数が 1 以上の値を持つ場合に、
.Fn atanh
はグローバル変数
.Va errno
を
.Er EDOM
に設定し、予約されたオペランドフォルトが生成されます。
.Sh 関連項目
.Xr acosh 3 ,
.Xr asinh 3 ,
.Xr exp 3 ,
.Xr math 3
.Sh 歴史
.Fn atanh
関数は、
.Bx 4.3
で登場しました。