/*
* Open Source Physics software is free software as described near the bottom of this code file.
*
* For additional information and documentation on Open Source Physics please see:
* <http://www.opensourcephysics.org/>
*/
package org.opensourcephysics.numerics.specialfunctions;
import org.opensourcephysics.numerics.Function;
/**
* Computes the error function for a real argument.
*
* Can be instantiated as a Function or can be used with static methods.
*
*/
public class ErrorFunction implements Function {
/**
* Evaluates the error function in order to implement the Function interface.
*
* @param x
* @return error function at x
*/
public double evaluate(double x) {
return errf(x);
}
/**
* Error function.
* @param x
* @return value of error function at x
*/
public static double errf(double x) {
if(x>26.0) {
return 1.0;
} else if(x<-5.5) {
return -1.0;
} else {
double absx, c, p, q;
absx = Math.abs(x);
if(absx<=0.5) {
c = x*x;
p = ((-0.356098437018154e-1*c+0.699638348861914e1)*c+0.219792616182942e2)*c+0.242667955230532e3;
q = ((c+0.150827976304078e2)*c+0.911649054045149e2)*c+0.215058875869861e3;
return x*p/q;
}
if(x<0.0) {
return -(1.0-Math.exp(-x*x)*nonexperfc(absx));
}
return 1.0-Math.exp(-x*x)*nonexperfc(absx);
}
}
private static double nonexperfc(double x) {
double absx, c, p, q;
absx = Math.abs(x);
if(absx<=0.5) {
return Math.exp(x*x)*errf(x);
} else if(absx<4.0) {
c = absx;
p = ((((((-0.136864857382717e-6*c+0.564195517478974e0)*c+0.721175825088309e1)*c+0.431622272220567e2)*c+0.152989285046940e3)*c+0.339320816734344e3)*c+0.451918953711873e3)*c+0.300459261020162e3;
q = ((((((c+0.127827273196294e2)*c+0.770001529352295e2)*c+0.277585444743988e3)*c+0.638980264465631e3)*c+0.931354094850610e3)*c+0.790950925327898e3)*c+0.300459260956983e3;
return((x>0.0) ? p/q : Math.exp(x*x)*2.0-p/q);
} else {
c = 1.0/x/x;
p = (((0.223192459734185e-1*c+0.278661308609648e0)*c+0.226956593539687e0)*c+0.494730910623251e-1)*c+0.299610707703542e-2;
q = (((c+0.198733201817135e1)*c+0.105167510706793e1)*c+0.191308926107830e0)*c+0.106209230528468e-1;
c = (c*(-p)/q+0.564189583547756)/absx;
return((x>0.0) ? c : Math.exp(x*x)*2.0-c);
}
}
}
/*
* Open Source Physics software is free software; you can redistribute
* it and/or modify it under the terms of the GNU General Public License (GPL) as
* published by the Free Software Foundation; either version 2 of the License,
* or(at your option) any later version.
* Code that uses any portion of the code in the org.opensourcephysics package
* or any subpackage (subdirectory) of this package must must also be be released
* under the GNU GPL license.
*
* This software is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* GNU General Public License for more details.
*
* You should have received a copy of the GNU General Public License
* along with this; if not, write to the Free Software
* Foundation, Inc., 59 Temple Place, Suite 330, Boston MA 02111-1307 USA
* or view the license online at http://www.gnu.org/copyleft/gpl.html
*
* Copyright (c) 2007 The Open Source Physics project
* http://www.opensourcephysics.org
*/