/*
* ChiSquaredFitMethod.java
*
* Created on August 15, 2002, 4:38 PM
*/
package hep.aida.ref.fitter.fitmethod;
import hep.aida.IFunction;
import hep.aida.IModelFunction;
import hep.aida.dev.IDevFitDataIterator;
import hep.aida.ext.IFitMethod;
/**
*
* @author The AIDA team @ SLAC.
*
*/
public class CleverChiSquaredFitMethod extends AbstractFitMethod {
private static String[] names = new String[]{"cleverchi2","cleverchisquared"};
public CleverChiSquaredFitMethod() {
super(IFitMethod.BINNED_FIT, names);
}
public double evaluateSumElement(IDevFitDataIterator dataIter, IFunction function) {
double fVal = function.value( dataIter.vars() );
return Math.pow( dataIter.value() - fVal , 2)/Math.abs(fVal);
}
public double[] evaluateGradientSumElement(IDevFitDataIterator dataIter, IFunction function) {
double f = function.value( dataIter.vars() );
double[] der = ((IModelFunction)function).parameterGradient( dataIter.vars() );
double[] newDer = new double[der.length];
double val = dataIter.value();
double d = (val-f);
double s = f > 0 ? 1 : -1;
double c = d*( -2*Math.abs(f) - d*s )/(f*f);
for ( int i = 0; i < der.length; i++ )
newDer[i] = der[i]*c;
return newDer;
}
}