erf.3m

<B>Digital的Unix操作系统VAX 4.2源码</B>

.TH erf 3m RISC
.ds nn \fINaN\fR
.SH Name
erf, erfc \- error functions
.SH Syntax
.nf
.B #include <math.h>
.PP
.B double erf(\fIx\fP)
.B double \fIx\fP;
.PP
.B double erfc(\fIx\fP)
.B double \fIx\fP;
.fi
.SH Description
.NXR "erf function"
.NXR "erfc function"
The 
.PN erf 
function returns the error function of
.I x
defined as follows:
.EX
erf(x) = 2/sqrt(pi)\(**\|integral from 0 to x of exp(\-t\(**t) dt. \}
.EE
.PP
The 
.PN erfc
function returns 1.0\-erf\|(\fIx\fP).
.PP
The entry for the
.PN erfc 
function is provided because of the extreme loss
of relative accuracy if erf\|(\fIx\fP) is called for large
.I x
and the result subtracted from 1.
For example if
.I x
= 10, 12 places are lost.
.SH Return Values
The
.PN erf
and
.PN erfc
functions return \*(nn when
.I x
is \*(nn.
.SH See Also
math(3m)