/* From: "COMPUTATIONAL PHYSICS, 2nd Ed" 
   by RH Landau, MJ Paez, and CC Bordeianu 
   Copyright Wiley-VCH, 2007.
   Electronic Materials copyright: R Landau, Oregon State Univ, 2007;
   MJ Paez, Univ Antioquia, 2007; & CC Bordeianu, Univ Bucharest, 2007
   Support by National Science Foundation                          
*/  
// Fit.java: Least square fit to tabulated data

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

  public static void main(String[] argv)  {
		
    int i, j;
    double s, sx, sy, sxx, sxy, delta, inter, slope;
    double x[] = new double[data]; double y[] = new double[data];
    double d[] = new double[data];
		                                                  // Input data x
    for (i = 0; i<data; i++) x[i] = i*180+5;              
		                                                  // Input data 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;  
		                                           // Input data delta y
    for (i = 0; i<data; i++) d[i] = 18.;             
    s = sx = sy = sxx = sxy = 0.;                        // Init sums
		                                                // Calculate sums
    for (i = 0;i<data;i++) {                             
      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.");
} }