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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.