erfc, erfcf, erfcl - complementary error function

```
#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
```

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

These functions return the complementary error function of `x`

, that is, 1.0 - erf(x).

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.

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`

.

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

Interface | Attribute | Value |

erfc(), erfcf(), erfcl() | Thread safety | MT-Safe |

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

The variant returning `double`

also conforms to SVr4, 4.3BSD.

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).

This page is part of release 4.15 of the Linux `man-pages`

project. A description of the project, information about reporting bugs, and the latest version of this page, can be found at https://www.kernel.org/doc/man-pages/.