net.maizegenetics.stats.math.ErrorFunction Maven / Gradle / Ivy

// ErrorFunction.java
//
// (c) 1999-2001 PAL Development Core Team
//
// This package may be distributed under the
// terms of the Lesser GNU General Public License (LGPL)


package net.maizegenetics.stats.math;


/**
 * error function and related stuff
 *
 * @version $Id: ErrorFunction.java,v 1.1 2007/01/12 03:26:15 tcasstevens Exp $
 *
 * @author Korbinian Strimmer
 */
public class ErrorFunction
{
	//
	// Public stuff
	//

	/**
	 * error function
	 *
	 * @param x argument
	 *
	 * @return function value
	 */
	public static double erf(double x)
	{
		if (x > 0.0)
		{
			return GammaFunction.incompleteGammaP(0.5, x*x);
		}
		else if (x < 0.0)
		{
			return -GammaFunction.incompleteGammaP(0.5, x*x);
		}
		else
		{
			return 0.0;
		}
	}
	
	/**
	 * complementary error function = 1-erf(x)
	 *
	 * @param x argument
	 *
	 * @return function value
	 */
	public static double erfc(double x)
	{
		return 1.0-erf(x);
	}

	
	/**
	 * inverse error function
	 *
	 * @param z argument
	 *
	 * @return function value
	 */
	public static double inverseErf(double z)
	{
		return pointNormal(0.5*z+0.5)/Math.sqrt(2.0);
	}


	// Private

	// Returns z so that Prob{x