# erfcl (3)

# NAME

erfc, erfcf, erfcl - complementary error function# SYNOPSIS

#include <math.h>

Link withdouble erfc(doublex);float erfcf(floatx);long double erfcl(long doublex);

*-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

|| /* 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

|| /* 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.

*errno*.

# ATTRIBUTES

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

Interface | Attribute | Value |

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

# 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)