# Man Page

## NAME

erfc, erfcf, erfcl - complementary error function

## 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(): _BSD_SOURCE || _SVID_SOURCE || _XOPEN_SOURCE || _ISOC99_SOURCE; or cc -std=c99
erfcf(), erfcl(): _BSD_SOURCE || _SVID_SOURCE || _XOPEN_SOURCE >= 600|| _ISOC99_SOURCE; or cc -std=c99

## DESCRIPTION

The erfc() function returns 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 floating-point exception (FE_UNDERFLOW) is raised.

These functions do not set errno.

## CONFORMING TO

C99, POSIX.1-2001. The variant returning double also conforms to SVr4, 4.3BSD.

## NOTES

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

cerf(3), erf(3), exp(3)

## COLOPHON

This page is part of release 3.24 of the Linux man-pages project. A description of the project, and information about reporting bugs, can be found at http://www.kernel.org/doc/man-pages/.

NAME
SYNOPSIS
DESCRIPTION
RETURN VALUE
ERRORS
CONFORMING TO
NOTES