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ERFC(3P)                   POSIX Programmer's Manual                  ERFC(3P)

PROLOG
       This  manual  page is part of the POSIX Programmer's Manual.  The Linux
       implementation of this interface may differ (consult the  corresponding
       Linux  manual page for details of Linux behavior), or the interface may
       not be implemented on Linux.
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 imple-
       mentation-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 Condi-
       tions 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 .

IEEE/The Open Group                  2003                             ERFC(3P)