/* 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; and CC Bordeianu, Univ Bucharest, 2007.
   Support by National Science Foundation                              
*/
// IntegGauss.java: Gauss quadrature, need include gauss method

import java.io.*;                          // Location of PrintWriter

public class IntegGauss  {
  static final double max_in = 1001;                // Numb intervals
  static final double vmin = 0., vmax = 1.;             // Int ranges
  static final double ME = 2.7182818284590452354E0 ; // Euler's const

 public static void main(String[] argv) 
                       throws IOException, FileNotFoundException {
   int i; 
   double result;  
	 
   PrintWriter t = new PrintWriter(
                   new FileOutputStream("IntegGauss.dat"), true); 
   for ( i=3;  i <= max_in;  i  += 2) {  
     result = gaussint(i, vmin, vmax); 
     t.println("" + i + " " + Math.abs(result-1 + 1/ME)); 
   }  
   System.out.println("Output in IntegGauss.dat");   
  }
                                                             // f(x)
  public static double f (double x)      {return (Math.exp(-x));} 

  public static double gaussint (int no, double min, double max)  {
    int n;              
    double quadra = 0.; 
    double w[] = new double[2001], x[] = new double[2001];    
    Gauss.gauss (no, 0, min, max, x, w);         // Returns pts & wts
    for ( n=0;  n <  no;  n++ )  { 
      quadra += f(x[n])*w[n]; }                 // Calculate integral
    return (quadra);                   
  }
}