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The following is a set of java examples that illustrate how to perform relatively simple fits. These examples can be compiled and run as standalone programs using JAIDA (see the JAIDA Release Notes) or they can be loaded, compiled and run within JAS3.

Chi2GaussianFit.java

import hep.aida.*;
import java.util.Random;

public class Chi2GaussianFit {
    
        
    public static void main(String[] argv) {
        
         // Create the AIDA factories
        IAnalysisFactory    analysisFactory = IAnalysisFactory.create();
        ITree                    tree = analysisFactory.createTreeFactory().create();
        IHistogramFactory histogramFactory = analysisFactory.createHistogramFactory(tree);
        IFunctionFactory    functionFactory = analysisFactory.createFunctionFactory(tree);
        IFitFactory             fitFactory = analysisFactory.createFitFactory();

        // Create a random number generator
        Random r = new Random();
         
        // Create a 1D histogram. Fill it with a set of random gaussian distributed data
        IHistogram1D h1 = histogramFactory.createHistogram1D("Histogram 1D",50,-6,6);
        
        for (int i=0; i<100000; i++)
            h1.fill(r.nextGaussian());
    
        // Create a gaussian and set its parameters
        IFunction gauss = functionFactory.createFunctionByName("gauss","g");
        gauss.setParameter("amplitude",h1.maxBinHeight());
        gauss.setParameter("mean",h1.mean());
        gauss.setParameter("sigma",h1.rms());
                
        // Create the fitter, with chi squared as fit method and Minuit as fit engine
        IFitter fitter = fitFactory.createFitter("chi2","minuit");
 
        // Fit  the histogram with the gaussian function
        IFitResult result = fitter.fit(h1,gauss);

        // Create a plotter and display the result of the fit
        IPlotter plotter = analysisFactory.createPlotterFactory().create("Plotter");
        plotter.region(0).plot(h1);
        plotter.region(0).plot(result.fittedFunction());
        plotter.show();
    }
}
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