/* 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                              
*/
//  harmos.java: Solution t-dependent Schroedinger equation for 
//            Gaussian wavepacket in a harmonic oscillator potential

import java.io.*;

public class harmos  {

  public static void main(String[] argv) 
                       throws IOException, FileNotFoundException  {
				
    PrintWriter w = 
        new PrintWriter(new FileOutputStream("Harmos.dat"), true);
    double psr[][] = new double[751][2];
    double psi[][] = new double[751][2];
    double p2[] = new double[751];
    double v[] = new double[751];
    double dx=0.02, k0, dt, x, pi;
    int i ,n, max = 750;
		
    pi   = 3.14159265358979323846;
    k0   = 3.0*pi;
    dt   = dx*dx/4.0;   
    x   = -7.5;                                      
		                                            // Initial conditions
    for ( i=0; i<max; i++)  {       
      psr[i][0] = Math.exp(-0.5*(Math.pow((x/0.5),2.0)))
                                        *Math.cos(k0*x);     // RePsi
      psi[i][0] = Math.exp(-0.5*(Math.pow((x/0.5),2.0)))
                                        *Math.sin(k0*x);     // ImPsi
      v[i] = 5.0*x*x;                                    // Potential
      x    = x + dx;
    }
		                                             // Propagate in time
    for ( n=0; n<20000; n++)  {                       
      for ( i=1; i<max-1; i++ )  {                           // RePsi
        psr[i][1] = psr[i][0] - dt*(psi[i+1][0] + psi[i-1][0]    
                   -2.0*psi[i][0])/(dx*dx)+dt*v[i]*psi[i][0];
        p2[i] = psr[i][0]*psr[i][1]+psi[i][0]*psi[i][0];            
      }
      for ( i=1; i<max-1; i++ )  {                           // ImPsi
        psi[i][1] = psi[i][0] + dt*(psr[i+1][1] + psr[i-1][1]
                   -2.0*psr[i][1])/(dx*dx)-dt*v[i]*psr[i][1];  
      } 
			                                     // Output every 2000 steps
      if ( (n == 0) || (n%2000 == 0) ) {         
        for (i=0;i<max; i=i+10) w.println(""+(p2[i]+0.0015*v[i])+"");
           w.println("");   
      }     
      for ( i=0; i<max; i++ )  {                        // New -> old
        psi[i][0] = psi[i][1];
        psr[i][0] = psr[i][1];
      } 
    }
    System.out.println("data saved in Harmos.dat");
  }
}