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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
       The functionality described on this reference page is aligned with  the
       ISO C  standard.  Any  conflict between the requirements described here
       and the ISO C standard is unintentional. This  volume  of  POSIX.1-2008
       defers to the ISO C standard.
       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 erfc(), erfcf(), and  erfcl()  shall  return
       0.0,  or  (if  the IEC 60559 Floating-Point option is not supported) an
       implementation-defined value no  greater  in  magnitude  than  DBL_MIN,
       FLT_MIN, and LDBL_MIN, respectively.
       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 under-
       flowed.
       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 POSIX.1-2008, Section 4.19, 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, 2013 Edition, Standard for Information Technology
       -- Portable Operating System Interface (POSIX),  The  Open  Group  Base
       Specifications Issue 7, Copyright (C) 2013 by the Institute of Electri-
       cal and Electronics Engineers,  Inc  and  The  Open  Group.   (This  is
       POSIX.1-2008  with  the  2013  Technical Corrigendum 1 applied.) 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.unix.org/online.html .
       Any  typographical  or  formatting  errors that appear in this page are
       most likely to have been introduced during the conversion of the source
       files  to  man page format. To report such errors, see https://www.ker-
       nel.org/doc/man-pages/reporting_bugs.html .
IEEE/The Open Group                  2013                             ERFC(3P)