From Prof. Kahan at UC at Berkeley
.EQ
delim $$
.EN
.TH ERF 3M  "9 May 1985"
.SH NAME
erf, erfc \- error functions
.SH SYNOPSIS
.nf
.B #include <math.h>
.PP
.B double erf(x)
.B double x;
.PP
.B double erfc(x)
.B double x;
.fi
.SH DESCRIPTION
.I Erf(x)
returns the error function of 
.I x.
.PP
.I Erfc(x)
returns
.I 1.0\-erf(x).
.PP
.I Erf(x)
is defined by
${2 over sqrt {pi}} int from 0 to x e sup {-t sup 2} dt$.
.PP
The entry for
.I erfc
is provided because of the extreme loss of relative accuracy if
.I erf(x)
is called for large
.I x
and the result subtracted from 1.
(e.g. for
.I x
= 10, 12 places are lost).
.SH SEE ALSO
intro(3M)