erf,
erff,
erfc,
erfcf
[error function]
SYNOPSIS
#include <math.h>
double erf(double x);
float erff(float x);
double erfc(double x);
float erfcf(float x);
DESCRIPTION
erf
calculates an approximation to the
error function which estimates the probability that an observation
will fall within x
standard deviations of the mean (assuming
a normal distribution).
The error function is defined as the following equation.
erfc calculates the complementary probability; that is, erfc(x) is 1 - erf(x). erfc is computed directly, so that you can use it to avoid the loss of precision that would result from subtracting large probabilities (on large x) from 1.
erff and erfcf differ from erf and erfc only in the argument and result types.
RETURNS
For positive arguments, erf
and all its variants return a probability—a
number between 0 and 1.
COMPLIANCE
None of the variants of erf
are ANSI C.