### 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.
| |

*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

### COLOPHON

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