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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();
    }
}