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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 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 .