
ERFC(P) POSIX Programmer's Manual ERFC(P)
NAME
erfc, erfcf, erfcl  complementary error functions
SYNOPSIS
#include <math.h>
double erfc(double x);
float erfcf(float x);
long double erfcl(long double x);
DESCRIPTION
These functions shall compute the complementary error function 1.0  erf(x).
An application wishing to check for error situations should set errno to zero and call
feclearexcept(FE_ALL_EXCEPT) before calling these functions. On return, if errno is non
zero or fetestexcept(FE_INVALID  FE_DIVBYZERO  FE_OVERFLOW  FE_UNDERFLOW) is nonzero,
an error has occurred.
RETURN VALUE
Upon successful completion, these functions shall return the value of the complementary
error function.
If the correct value would cause underflow and is not representable, a range error may
occur and either 0.0 (if representable), or an implementationdefined value shall be
returned.
If x is NaN, a NaN shall be returned.
If x is +0, +1 shall be returned.
If x is Inf, +2 shall be returned.
If x is +Inf, +0 shall be returned.
If the correct value would cause underflow and is representable, a range error may occur
and the correct value shall be returned.
ERRORS
These functions may fail if:
Range Error
The result underflows.
If the integer expression (math_errhandling & MATH_ERRNO) is nonzero, then errno shall be
set to [ERANGE]. If the integer expression (math_errhandling & MATH_ERREXCEPT) is non
zero, then the underflow floatingpoint exception shall be raised.
The following sections are informative.
EXAMPLES
None.
APPLICATION USAGE
The erfc() function is provided because of the extreme loss of relative accuracy if erf(x)
is called for large x and the result subtracted from 1.0.
Note for IEEE Std 7541985 double, 26.55 < x implies erfc( x) has underflowed.
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 nonzero.
RATIONALE
None.
FUTURE DIRECTIONS
None.
SEE ALSO
erf() , feclearexcept() , fetestexcept() , isnan() , the Base Definitions volume of
IEEE Std 1003.12001, Section 4.18, Treatment of Error Conditions for Mathematical Func
tions, <math.h>
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) 20012003 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 orig
inal Standard can be obtained online at http://www.opengroup.org/unix/online.html .
IEEE/The Open Group 2003 ERFC(P) 
