.\" Copyright (c) 1985, 1991 Regents of the University of California.
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.\"     from: @(#)erf.3	6.4 (Berkeley) 4/20/91
.\" %FreeBSD: src/lib/msun/man/erf.3,v 1.5.2.4 2001/12/17 10:08:36 ru Exp %
.\"
.\" $FreeBSD$
.Dd April 20, 1991
.Dt ERF 3
.Os
.Sh 名称
.Nm erf ,
.Nm erff ,
.Nm erfc ,
.Nm erfcf
.Nd 誤差関数の演算子
.Sh ライブラリ
.Lb libm
.Sh 書式
.In math.h
.Ft double
.Fn erf "double x"
.Ft float
.Fn erff "float x"
.Ft double
.Fn erfc "double x"
.Ft float
.Fn erfcf "float x"
.Sh 解説
これらの関数は
.Fa x
の誤差関数を計算します。
.Pp
.Fn erf
関数と
.Fn erff
関数は、次のように、x の誤差関数 (error function) を計算します。
.Bd -ragged -offset indent
.if n \{\
erf(x) = 2/sqrt(pi)\(**\|integral from 0 to x of exp(\-t\(**t) dt \}
.if t \{\
erf\|(x) :=
(2/\(sr\(*p)\|\(is\d\s8\z0\s10\u\u\s8x\s10\d\|exp(\-t\u\s82\s10\d)\|dt \}
.Ed
.Pp
.Fn erfc
関数と
.Fn erfcf
関数は
.Fa x
の相補誤差関数 (complementary error function) を計算します。すなわち、
.Fn erfc
は 1.0 から誤差関数
.Fn erf x
の結果を減算します。
大きな
.Fa x
に対しては桁が失われてしまうため、この関数が有用です。
.Sh 関連項目
.Xr math 3
.Sh 歴史
.Fn erf
と
.Fn erfc
関数は
.Bx 4.3
で登場しました。