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


public class photons
{
   static StringTokenizer st;

   public static void main(String[] args) throws IOException
   {

     Integer np = 53;
     Double lambda[]     = new Double[53];
     Double delta[]         = new Double[52];
     Double probability[] = new Double[53];

      // Create factories
      IAnalysisFactory  analysisFactory = IAnalysisFactory.create();
      ITreeFactory      treeFactory = analysisFactory.createTreeFactory();
      ITree                tree = treeFactory.create();
      IPlotter             plotter = analysisFactory.createPlotterFactory().create("Fit.java Plot");
      IHistogramFactory histogramFactory = analysisFactory.createHistogramFactory(tree);
      IFunctionFactory  functionFactory = analysisFactory.createFunctionFactory(tree);
      IFitFactory          fitFactory = analysisFactory.createFitFactory();
      IDataPointSetFactory dpsf   = analysisFactory.createDataPointSetFactory(tree);

      IDataPointSet dataPointSet = dpsf.create("dataPointSet","Showing relation between wavelength and photomultiplier efficiency",2);
      // create data point set ; still empty

      try {
        BufferedReader in = new BufferedReader(new FileReader("C:\\Users\\Dawnimus\\Desktop\\data\\xp3422.txt"));    // read input file
        int i= 0;
        while ( true ){
          String line = in.readLine();                          // copy full line to string
          if (line==null) break;                                // abort loop if line is empty
          System.out.println( line );
          st = new StringTokenizer(line);                       // break line into tokens
          Double x  = Double.parseDouble(st.nextToken());
          Double y  = Double.parseDouble(st.nextToken()) * (0.34 /  89.400);  // convert into quantum efficiency
          System.out.println("(x,y)  "+  x + "  " + y );
          lambda[i] = x;
          probability[i] = y;
          if (i > 0){ delta[i-1] = lambda[i] - lambda[i-1];};
          IDataPoint dp = dataPointSet.addPoint();   // add one data point to set
          dp.coordinate(0).setValue(x);
          dp.coordinate(1).setValue(y);
          dp.coordinate(1).setErrorPlus(0.0);
          dp.coordinate(1).setErrorMinus(0.0);
          i++;
          }
       }
       catch (IOException e){System.out.println( e ); }


      Double alpha = 1.0 / 137.0 ;
      Double dNdz = 0. ;
      Double a=0. ;
      Double twopi = 8. * Math.atan(1.0);
      Double deg2rad = 360. / twopi;
      Double theta = 50.0 * deg2rad;
      for (int i = 0; i < np - 1; i++ ) {
          a = alpha * Math.pow(Math.sin(theta),2) * twopi *  Math.pow(lambda[i],-2) * delta[i] * 1e+9 ;
          dNdz = dNdz + a * probability[i] ;
           }

        System.out.println("dNdz  [1/m] : " + dNdz  );


       plotter.region(0).plot(dataPointSet);          // request plot
       plotter.show();   // show plot

       tree.close();

   }
}
\end{lstlisting}