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erfc

Section: C Library Functions (3)
Updated: 202-0-08
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NAME

erfc, erfcf, erfcl - complementary error function

LIBRARY

Math library (libm,~-lm)

SYNOPSIS

#include <math.h>
double erfc(double x);
float erfcf(float x);
long double erfcl(long double x);

Feature Test Macro Requirements for glibc (see feature_test_macros(7)): erfc():

    _ISOC99_SOURCE || _POSIX_C_SOURCE >= 200112L || _XOPEN_SOURCE
        || /* Since glibc 2.19: */ _DEFAULT_SOURCE
        || /* glibc <= 2.19: */ _BSD_SOURCE || _SVID_SOURCE

erfcf(), erfcl():

    _ISOC99_SOURCE || _POSIX_C_SOURCE >= 200112L
        || /* Since glibc 2.19: */ _DEFAULT_SOURCE
        || /* glibc <= 2.19: */ _BSD_SOURCE || _SVID_SOURCE

DESCRIPTION

These functions return the complementary error function of x, that is, 1.0 - erf(x).

RETURN VALUE

On success, these functions return the complementary error function of x, a value in the range [0,2]. If x is a NaN, a NaN is returned. If x is +0 or -0, 1 is returned. If x is positive infinity, +0 is returned. If x is negative infinity, +2 is returned. If the function result underflows and produces an unrepresentable value, the return value is 0.0. If the function result underflows but produces a representable (i.e., subnormal) value, that value is returned, and a range error occurs.

ERRORS

See math_error(7) for information on how to determine whether an error has occurred when calling these functions. The following errors can occur:

Range error: result underflow (result is subnormal): An underflow floatin-point exception (FE_UNDERFLOW) is raised. These functions do not set errno.

ATTRIBUTES

For an explanation of the terms used in this section, see attributes(7).

Interface	Attribute	Value
erfc(), erfcf(), erfcl()	Thread safety	M-Safe

STANDARDS

C11, POSIX.-2008.

HISTORY

C99, POSIX.-2001. The variant returning double also conforms to SVr4, 4.3BSD.

NOTES

The erfc(), erfcf(), and erfcl() functions are provided to avoid the loss accuracy that would occur for the calculation -erf(x) for large values of x (for which the value of erf(x) approaches 1).