//Ref: erfc: http://dic.academic.ru/dic.nsf/ruwiki/453940
// Definition at MatLab: http://www.mathworks.com/access/helpdesk/help/techdoc/index.html?/access/helpdesk/help/techdoc/ref/erf.html&http://www.mathworks.com/cgi-bin/texis/webinator/search/?db=MSS&prox=page&rorder=750&rprox=750&rdfreq=500&rwfreq=500&rlead=250&sufs=0&order=r&is_summary_on=1&ResultCount=10&query=erf&submitButtonName=Search
// We put commons-math.jar in
// C:\Program Files\Java\j2re1.4.2_13\lib\ext and in
// C:\Program Files\Java\jre1.5.0_10\lib\ext
// Added this: import org.apache.commons.math.special.*;
// Eclipse problems: access rules:
// Way around: http://lkamal.blogspot.com/2008/09/eclipse-access-restriction-on-library.html
// We used this: (Project) Properties -> Java Compiler -> Errors/Warnings
// We did not use this: Windows -> Preferences -> Java -> Compiler -> Errors/Warnings
// which stays different.
//
// Edit manually: http://www.eclipsezone.com/forums/thread.jspa?messageID=91952212
// doc: //http://www.java2s.com/Open-Source/Java-Document/Science/Apache-commons-math-1.1/org/apache/commons/math/special/Erf.java.htm
// java-doc: http://commons.apache.org/math/api-1.0/overview-summary.html
// download: http://www.java2s.com/Code/Jar/ABC/Downloadcommonsmath12jar.htm
// http://www.java2s.com/Code/Jar/CatalogJar.htm
// install: http://leepoint.net/notes-java/background/13files_and_directories/86packages-installing.html
//
import org.apache.commons.math.special.Erf;
public class UFun {
private final static boolean USECUSTOM=true;
public static double erfh(double x, boolean HeavisideMode){
if(HeavisideMode)return x>0 ? 0.0 :1.0 ;
if(USECUSTOM){
return UCFun.erfc(x);
}else{
return erfc(x);
}
}
//Apache version for test case:
public static double erfha(double x, boolean HeavisideMode){
if(HeavisideMode)return x>0 ? 0.0 :1.0 ;
return erfc(x);
}
//Wrapper to Apache library erf:
public static double erfc(double x){
if(x<0)return 1.0-erfc(-x);
try{
return (Erf.erf(-x*Math.sqrt(0.5))+1.0)*0.5;
}catch(Exception ex){
return 0;
}
}
//Test Case:
public static double erfDerivative(double x, double step){
return (erfc(x)-erfc(x+step))/step;
}
}
Copyright (C) 2009 Konstantin Kirillov