Name
erf, erff, erfl - error functionLibrary
Math library ( libm ", " -lm )Synopsis
#include <math.h> double erf(double x );Feature Test Macro Requirements for glibc (see feature_test_macros(7)):
float erff(float x );
long double erfl(long double x );
erf()
_ISOC99_SOURCE || _POSIX_C_SOURCE >= 200112L || _XOPEN_SOURCE || /* Since glibc 2.19: */ _DEFAULT_SOURCE || /* glibc <= 2.19: */ _BSD_SOURCE || _SVID_SOURCE
erff() erfl()
_ISOC99_SOURCE || _POSIX_C_SOURCE >= 200112L || /* Since glibc 2.19: */ _DEFAULT_SOURCE || /* glibc <= 2.19: */ _BSD_SOURCE || _SVID_SOURCE
Description
These functions return the error function ofx
, defined as erf(x) = 2/sqrt(pi) * integral from 0 to x of exp(-t*t) dt
Return Value
On success, these functions return the value of the error function ofx
, a value in the range [-1,\ 1]. If x is a NaN, a NaN is returned.
If x is +0 (-0), +0 (-0) is returned.
If x is positive infinity (negative infinity), +1 (-1) is returned.
If x is subnormal, a range error occurs, and the return value is 2*x/sqrt(pi).
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 (x 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).Interface | Attribute | Value |
T} | Thread safety | MT-Safe |
Standards
C11, POSIX.1-2008.History
C99, POSIX.1-2001.The variant returning double also conforms to SVr4, 4.3BSD.