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ERFC(P)POSIX Programmer's Manual ERFC(P)NAMEerfc, erfcf, erfcl - complementary error functionsSYNOPSIS#include <math.h> double erfc(double x); float erfcf(float x); long double erfcl(long double x);DESCRIPTIONThese 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 VALUEUpon 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, +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.-InfERRORSThese 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.EXAMPLESNone.APPLICATION USAGEThe 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.RATIONALENone.FUTURE DIRECTIONSNone.SEE ALSOerf() , feclearexcept() , fetestexcept() , isnan() , the Base Definitions volume of IEEE Std 1003.1-2001, Section 4.18, Treatment of Error Conditions for Mathematical Func- tions, <math.h>COPYRIGHTPortions of this text are reprinted and reproduced in electronic form from IEEE Std 1003.1, 2003 Edition, Standard for Information TechnologyPortable 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 orig- inal Standard can be obtained online at http://www.opengroup.org/unix/online.html .--IEEE/The Open Group 2003 ERFC(P)

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