# ERFC

NAME

SYNOPSIS

DESCRIPTION

RETURN VALUE

ERRORS

ATTRIBUTES

CONFORMING TO

NOTES

SEE ALSO

COLOPHON

## 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***);**

Link with
*-lm*.

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 versions <= 2.19: */ _BSD_SOURCE ||
_SVID_SOURCE

**erfcf**(),
**erfcl**():

_ISOC99_SOURCE ||
_POSIX_C_SOURCE >= 200112L

|| /* Since glibc 2.19: */ _DEFAULT_SOURCE

|| /* Glibc versions <= 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 floating-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).

## CONFORMING TO

C99,
POSIX.1-2001, POSIX.1-2008.

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 1-erf(x) for large values of *x* (for
which the value of erf(x) approaches 1).

## SEE ALSO

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

## COLOPHON

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