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 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 Technol-
       ogy -- 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 .

IEEE
/The Open Group						       2003								   ERFC(P)