/* From: "COMPUTATIONAL PHYSICS, 2nd Ed" 
   by RH Landau, MJ Paez, and CC Bordeianu 
   Copyright Wiley-VCH, 2008.
   Electronic Materials copyright: R Landau, Oregon State Univ, 2008;
   MJ Paez, Univ Antioquia, 2008; & CC Bordeianu, Univ Bucharest, 2008
   Support by National Science Foundation                          
*/  
// Fit.java: Least square fit to tabulated data
import java.io.*;   

public class Fit  { 
	static int  data =  12;                                    // Number of data points

  public static void main(String[] argv)throws IOException, FileNotFoundException {
    PrintWriter w = new PrintWriter(new FileOutputStream("fit.dat"), true);
		int i, j;
    double s, sx, sy, sxx, sxy, delta, inter, slope, yy;
    double x[] = new double[data], y[] = new double[data], d[] = new double[data];
    for (i = 0; i<data; i++) x[i] = i*180+5;                            // Input x, y
		y[0] = 382; y[1] = 187;  y[2] = 281; y[3] = 78;   y[4]  = 88; y[5] = 86;
		y[6] = 85;  y[7] = 28;   y[8] = 28;  y[9] = 0.81; y[10] = 84; y[11] = 81;
		for (i = 0; i<data; i++) d[i] = 18.;                        // Input data delta y
		s = sx = sy = sxx = sxy = 0.;                                        // Init sums
		for (i = 0;i<data;i++) {                                        // Calculate sums
      s   +=         1. / (d[i]*d[i]);
      sx  +=       x[i] / (d[i]*d[i]);
      sy  +=       y[i] / (d[i]*d[i]); 
      sxx +=  x[i]*x[i] / (d[i]*d[i]); 
      sxy +=  x[i]*y[i] / (d[i]*d[i]);
    } 
    delta  =  s*sxx - sx*sx;
    slope =   (s*sxy - sx*sy) / delta; 
    inter = (sxx*sy - sx*sxy) / delta; 
    System.out.println("intercpt= "+inter+", "+Math.sqrt(sxx/delta));
    System.out.println("slope =  "+slope+" , "+Math.sqrt(s/delta));
    System.out.println("Fit Program Complete.");
    for(i=0;i<data;i++){yy=slope*x[i]+inter; w.println(" "+x[i]+"  "+yy +"  "+y[i]);}
  }
}