.\" Copyright (c) 2001-2003 The Open Group, All Rights Reserved 
.TH "ERFC" P 2003 "IEEE/The Open Group" "POSIX Programmer's Manual"
.\" erfc 
.SH NAME
erfc, erfcf, erfcl \- complementary error functions
.SH SYNOPSIS
.LP
\fB#include <math.h>
.br
.sp
double erfc(double\fP \fIx\fP\fB);
.br
float erfcf(float\fP \fIx\fP\fB);
.br
long double erfcl(long double\fP \fIx\fP\fB);
.br
\fP
.SH DESCRIPTION
.LP
These functions shall compute the complementary error function 1.0
- \fIerf\fP(\fIx\fP).
.LP
An application wishing to check for error situations should set \fIerrno\fP
to zero and call
\fIfeclearexcept\fP(FE_ALL_EXCEPT) before calling these functions.
On return, if \fIerrno\fP is non-zero or
\fIfetestexcept\fP(FE_INVALID | FE_DIVBYZERO | FE_OVERFLOW | FE_UNDERFLOW)
is non-zero, an error has occurred.
.SH RETURN VALUE
.LP
Upon successful completion, these functions shall return the value
of the complementary error function.
.LP
If the correct value would cause underflow and is not representable,
a range error may occur and   \ either 0.0 (if
representable), or  an implementation-defined value shall be
returned.
.LP
If
\fIx\fP is NaN, a NaN shall be returned.
.LP
If \fIx\fP is \(+-0, +1 shall be returned.
.LP
If \fIx\fP is -Inf, +2 shall be returned.
.LP
If \fIx\fP is +Inf, +0 shall be returned.
.LP
If the correct value would cause underflow and is representable, a
range error may occur and the correct value shall be
returned. 
.SH ERRORS
.LP
These functions may fail if:
.TP 7
Range\ Error
The result underflows. 
.LP
If the integer expression (math_errhandling & MATH_ERRNO) is non-zero,
then \fIerrno\fP shall be set to [ERANGE]. If the
integer expression (math_errhandling & MATH_ERREXCEPT) is non-zero,
then the underflow floating-point exception shall be
raised.
.sp
.LP
\fIThe following sections are informative.\fP
.SH EXAMPLES
.LP
None.
.SH APPLICATION USAGE
.LP
The \fIerfc\fP() function is provided because of the extreme loss
of relative accuracy if \fIerf\fP(\fIx\fP) is called for
large \fIx\fP and the result subtracted from 1.0.
.LP
Note for IEEE\ Std\ 754-1985 \fBdouble\fP, 26.55 < \fIx\fP implies
\fIerfc\fP( \fIx\fP) has underflowed.
.LP
On error, the expressions (math_errhandling & MATH_ERRNO) and (math_errhandling
& MATH_ERREXCEPT) are independent of
each other, but at least one of them must be non-zero.
.SH RATIONALE
.LP
None.
.SH FUTURE DIRECTIONS
.LP
None.
.SH SEE ALSO
.LP
\fIerf\fP() , \fIfeclearexcept\fP() , \fIfetestexcept\fP() , \fIisnan\fP()
, the Base Definitions volume of
IEEE\ Std\ 1003.1-2001, Section 4.18, Treatment of Error Conditions
for
Mathematical Functions, \fI<math.h>\fP
.SH COPYRIGHT
Portions of this text are reprinted and reproduced in electronic form
from IEEE Std 1003.1, 2003 Edition, Standard for Information Technology
-- Portable Operating System Interface (POSIX), The Open Group Base
Specifications Issue 6, Copyright (C) 2001-2003 by the Institute of
Electrical and Electronics Engineers, Inc and The Open Group. In the
event of any discrepancy between this version and the original IEEE and
The Open Group Standard, the original IEEE and The Open Group Standard
is the referee document. The original Standard can be obtained online at
http://www.opengroup.org/unix/online.html .