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.TH ERFC 3  2010-09-20 "GNU" "Linux Programmer's Manual"
.SH NAME
erfc, erfcf, erfcl \- complementary error function
.SH SYNOPSIS
.nf
.B #include <math.h>

.BI "double erfc(double " x );
.BI "float erfcf(float " x );
.BI "long double erfcl(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 erfc ():
.RS 4
_BSD_SOURCE || _SVID_SOURCE || _XOPEN_SOURCE || _ISOC99_SOURCE ||
_POSIX_C_SOURCE\ >=\ 200112L;
.br
or
.I cc\ -std=c99
.RE
.br
.BR erfcf (),
.BR erfcl ():
.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 erfc ()
function returns the complementary error function of
.IR x ,
that is, 1.0 \- erf(x).
.SH RETURN VALUE
On success, these functions return the complementary error function of
.IR x ,
a value in the range [0,2].

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

If
.I x
is +0 or \-0, 1 is returned.

If
.I x
is positive infinity,
+0 is returned.

If
.I x
is negative infinity,
+2 is returned.

If the function result underflows and produces an unrepresentable value,
the return value is 0.0.

If the function result underflows but produces a representable
(i.e., subnormal) value,
.\" e.g., erfc(27) on x86-32
that value is returned, and
a range error occurs.
.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 (result 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 NOTES
The
.BR erfc ()
functions are provided to avoid the loss accuracy that
would occur for the calculation 1-erf(x) for large values of
.IR x
(for which the value of erf(x) approaches 1).
.SH SEE ALSO
.BR cerf (3),
.BR erf (3),
.BR exp (3)