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ERFC(P) 			    POSIX Programmer's Manual				  ERFC(P)

       erfc, erfcf, erfcl - complementary error functions

       #include <math.h>

       double erfc(double x);
       float erfcf(float x);
       long double erfcl(long double x);

       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.

       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

       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.

       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.


       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.



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

       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 orig-
       inal Standard can be obtained online at http://www.opengroup.org/unix/online.html .

IEEE/The Open Group			       2003					  ERFC(P)
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