double erfc(doublex);
float erfcf(floatx);
long double erfcl(long doublex);

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 non-zero, 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 implementation-defined 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 non-zero,
then errno 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.

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 754-1985 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 non-zero.

RATIONALE

None.

FUTURE DIRECTIONS

None.

SEE ALSO

erf() , feclearexcept() , fetestexcept() , isnan()
, the Base Definitions volume of
IEEE Std 1003.1-2001, Section 4.18, Treatment of Error Conditions
for
Mathematical Functions, <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) 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 .