Package org.apache.commons.math.special

Class Erf

java.lang.Object

org.apache.commons.math.special.Erf

public class Erf
extends Object

This is a utility class that provides computation methods related to the error functions.

Method Summary

Modifier and Type	Method	Description
static double	erf(double x)	Returns the error function
static double	erfc(double x)	Returns the complementary error function

Methods inherited from class java.lang.Object

equals, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Method Detail

erf

public static double erf(double x)
                  throws MathException

Returns the error function

erf(x) = 2/√π ₀∫^x e^-t2dt

This implementation computes erf(x) using the regularized gamma function, following Erf, equation (3)

The value returned is always between -1 and 1 (inclusive). If abs(x) > 40, then erf(x) is indistinguishable from either 1 or -1 as a double, so the appropriate extreme value is returned.

Parameters:

x - the value.

Returns:

the error function erf(x)

Throws:

MathException - if the algorithm fails to converge.

See Also:

Gamma.regularizedGammaP(double, double, double, int)

erfc

public static double erfc(double x)
                   throws MathException

Returns the complementary error function

erfc(x) = 2/√π _x∫^∞ e^-t2dt
= 1 - erf(x)

This implementation computes erfc(x) using the regularized gamma function, following Erf, equation (3).

The value returned is always between 0 and 2 (inclusive). If abs(x) > 40, then erf(x) is indistinguishable from either 0 or 2 as a double, so the appropriate extreme value is returned.

Parameters:

x - the value

Returns:

the complementary error function erfc(x)

Throws:

MathException - if the algorithm fails to converge

Since:

2.2

See Also:

Gamma.regularizedGammaQ(double, double, double, int)