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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 .