relibc_openlibm/man/erf.3

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.\"     from: @(#)erf.3	6.4 (Berkeley) 4/20/91
.\" $FreeBSD: src/lib/msun/man/erf.3,v 1.12 2007/01/09 01:02:05 imp Exp $
.\"
.Dd April 20, 1991
.Dt ERF 3
.Os
.Sh NAME
.Nm erf ,
.Nm erff ,
.Nm erfc ,
.Nm erfcf
.Nd error function operators
.Sh LIBRARY
.Lb libm
.Sh SYNOPSIS
.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 DESCRIPTION
These functions calculate the error function of
.Fa x .
.Pp
The
.Fn erf
and the
.Fn erff
functions calculate the error function of x; where
.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
The
.Fn erfc
and the
.Fn erfcf
functions calculate the complementary error function of
.Fa x ;
that is
.Fn erfc
subtracts the result of the error function
.Fn erf x
from 1.0.
This is useful, since for large
.Fa x
places disappear.
.Sh SEE ALSO
.Xr math 3
.Sh HISTORY
The
.Fn erf
and
.Fn erfc
functions appeared in
.Bx 4.3 .