.\" Copyright 1993 David Metcalfe (david@prism.demon.co.uk)
.\" and Copyright 2008, Linux Foundation, written by Michael Kerrisk
.\"     <mtk.manpages@gmail.com>
.\"
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.\" manual provided the copyright notice and this permission notice are
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.\" manual under the conditions for verbatim copying, provided that the
.\" entire resulting derived work is distributed under the terms of a
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.\" Since the Linux kernel and libraries are constantly changing, this
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.\"
.\" References consulted:
.\"     Linux libc source code
.\"     Lewine's _POSIX Programmer's Guide_ (O'Reilly & Associates, 1991)
.\"     386BSD man pages
.\" Modified 1993-07-24 by Rik Faith (faith@cs.unc.edu)
.\" Modified 2002-07-27 by Walter Harms
.\" 	(walter.harms@informatik.uni-oldenburg.de)
.\"
.TH ERF 3  2010-09-20 "GNU" "Linux Programmer's Manual"
.SH NAME
erf, erff, erfl, \- error function
.SH SYNOPSIS
.nf
.B #include <math.h>

.BI "double erf(double " x );
.BI "float erff(float " x );
.BI "long double erfl(long double " x );

.fi
Link with \fI\-lm\fP.
.sp
.in -4n
Feature Test Macro Requirements for glibc (see
.BR feature_test_macros (7)):
.in
.sp
.ad l
.BR erf ():
.RS 4
_BSD_SOURCE || _SVID_SOURCE || _XOPEN_SOURCE || _ISOC99_SOURCE ||
_POSIX_C_SOURCE\ >=\ 200112L;
.br
or
.I cc\ -std=c99
.RE
.br
.BR erff (),
.BR erfl ():
.RS 4
_BSD_SOURCE || _SVID_SOURCE || _XOPEN_SOURCE\ >=\ 600 || _ISOC99_SOURCE ||
_POSIX_C_SOURCE\ >=\ 200112L;
.br
or
.I cc\ -std=c99
.RE
.ad b
.SH DESCRIPTION
The
.BR erf ()
function returns the error function of
.IR x ,
defined
as
.TP
    erf(x) = 2/sqrt(pi)* integral from 0 to x of exp(\-t*t) dt
.SH RETURN VALUE
On success, these functions return the error function of
.IR x ,
a value in the range [\-1,\ 1].

If
.I x
is a NaN, a NaN is returned.

If
.I x
is +0 (\-0), +0 (\-0) is returned.

If
.I x
is positive infinity (negative infinity),
+1 (\-1) is returned.

If
.I x
is subnormal,
a range error occurs,
and the return value is 2*x/sqrt(pi).
.SH ERRORS
See
.BR math_error (7)
for information on how to determine whether an error has occurred
when calling these functions.
.PP
The following errors can occur:
.TP
Range error: result underflow (\fIx\fP is subnormal)
.\" .I errno
.\" is set to
.\" .BR ERANGE .
An underflow floating-point exception
.RB ( FE_UNDERFLOW )
is raised.
.PP
These functions do not set
.IR errno .
.\" FIXME . Is it intentional that these functions do not set errno?
.\" Bug raised: http://sources.redhat.com/bugzilla/show_bug.cgi?id=6785
.SH CONFORMING TO
C99, POSIX.1-2001.
The variant returning
.I double
also conforms to
SVr4, 4.3BSD.
.SH SEE ALSO
.BR cerf (3),
.BR erfc (3),
.BR exp (3)
.SH COLOPHON
This page is part of release 3.53 of the Linux
.I man-pages
project.
A description of the project,
and information about reporting bugs,
can be found at
\%http://www.kernel.org/doc/man\-pages/.
