NAME
erf, erff, erfl - error function
SYNOPSIS
#include <math.h>
double
erf(double x);
float erff(float x);
long double erfl(long double x);
Link with -lm.
Feature Test Macro Requirements for glibc (see feature_test_macros(7)):
erf():
_ISOC99_SOURCE ||
_POSIX_C_SOURCE >= 200112L || _XOPEN_SOURCE
|| /* Since glibc 2.19: */ _DEFAULT_SOURCE
|| /* Glibc versions <= 2.19: */ _BSD_SOURCE ||
_SVID_SOURCE
erff(), erfl():
_ISOC99_SOURCE ||
_POSIX_C_SOURCE >= 200112L
|| /* Since glibc 2.19: */ _DEFAULT_SOURCE
|| /* Glibc versions <= 2.19: */ _BSD_SOURCE ||
_SVID_SOURCE
DESCRIPTION
These functions
return the error function of x, 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 of x, 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).
CONFORMING TO
C99, POSIX.1-2001, POSIX.1-2008.
The variant returning double also conforms to SVr4, 4.3BSD.
SEE ALSO
COLOPHON
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