///////////////////////////////////////////////////////////////////////////
//                                                                       //
// Program file name: Motion.java                                        //
//                                                                       //
// © Tao Pang 2006                                                       //
//                                                                       //
// Last modified: January 18, 2006                                       //
//                                                                       //
// (1) This Java program is part of the book, "An Introduction to        //
//     Computational Physics, 2nd Edition," written by Tao Pang and      //
//     published by Cambridge University Press on January 19, 2006.      //
//                                                                       //
// (2) No warranties, express or implied, are made for this program.     //
//                                                                       //
///////////////////////////////////////////////////////////////////////////
 
// An example of studying the motion of a particle in
// one dimension under an elastic force.

import java.lang.*;
public class Motion {
  static final int n = 100000, j = 500;
  public static void main(String argv[]) {
    double x[] = new double[n+1];
    double v[] = new double[n+1];

 // Assign time step and initial position and velocity
    double dt = 2*Math.PI/n;
    x[0] = 0;
    v[0] = 1;

 // Calculate other position and velocity recursively
    for (int i=0; i<n; ++i) {
      x[i+1] = x[i]+v[i]*dt;
      v[i+1] = v[i]-x[i]*dt;
    }

 // Output the result in every j time steps
    double t = 0;
    double jdt = j*dt;
    for (int i=0; i<=n; i+=j) {
      System.out.println(t +" " + x[i] + " " + v[i]);
      t += jdt;
    }
  }
}