**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**(): _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).

**SEE ALSO**

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

**COLOPHON**

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description of the project, and information about reporting bugs, can
be found at http://www.kernel.org/doc/man-pages/.