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 (con-
       sult 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 repre-
       sentable), 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 inte-
       ger 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, Copy-
       right (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.open-
       group.org/unix/online.html .



IEEE/The Open Group                                           2003                                                      ERFC(3P)