import java.awt.*;

import java.applet.*;
//copyright 2000 M Paez, U Antioquia, R landau, OSU


public class Sqwell extends Applet implements Runnable {

  Thread runstring;

  private Image offScreenImage;

  double mxx,bxx,myy,byy,pi,k0,dx;

  double psr[][],psi[][],p2[];

  int jj;

  int max;

  public void start()

  {

    if(runstring==null);

    {

     runstring=new Thread(this);

     runstring.start();

    }

  }

  public void stop()

  {

     if(runstring != null){

       runstring.stop();

       runstring=null;

     }

  }

  public void run()

  {

    while(true){

      repaint();

      try{ Thread.sleep(10);

      }

      catch(InterruptedException e){ }

    }

  }

  public void update(Graphics g)

  { //To avoid flicker

    Graphics offScreenGraphics=offScreenImage.getGraphics();

    offScreenGraphics.setColor(getBackground());

    offScreenGraphics.fillRect(0,0,size().width,size().height);

    offScreenGraphics.setColor(g.getColor());

    paint(offScreenGraphics);

    g.drawImage(offScreenImage,0,0,this);

  }



  void coormundo(double xiz,double ysu,double xde,double yinf)

  {

    double maxx,maxy,xxfin,xxcom,yyin,yysu;

    maxx=600;

    maxy=450;

    xxcom=0.15*maxx;

    xxfin=0.75*maxx;

    yyin=0.8*maxy;

    yysu=0.2*maxy;

    mxx=(xxfin-xxcom)/(xde-xiz);

    bxx=0.5*(xxcom+xxfin-mxx*(xiz+xde));

    myy=(yyin-yysu)/(yinf-ysu);

    byy=0.5*(yysu+yyin-myy*(yinf+ysu));

  }





  void ejes(double xmz,double yms,double xmd,double ymi,Graphics g)

  {

    //Grafica los ejes

    // La entrada esta en coordenadas 0.0 a 1.0

    int i,mp,xpi,xpd,yps,ypi,xdiv,ydiv,ypcen;

    double yincr,xincr,yte;

    //char nhorz[3],nver[15];

    char nver;

    int sig=4;

    ydiv=1;

    xpi=(int)(mxx*xmz+bxx);

    xpd=(int)(mxx*xmd+bxx);

    yps=(int)(myy*yms+byy);

    ypi=(int)(myy*ymi+byy);

    ypcen=(int)byy;

    g.drawLine(xpi,ypcen,xpd,ypcen);

 }

 public void Equation(Graphics g, int jj)

 {

   int peo,peye,pex,peyo;

   double dt,x,fact2;

   int i,n;

   dt=dx*dx;

   if(jj==1){

     // initial conditions

     x=0.0;

     for(i=0;i<max+1;i++){

       p2[i]=0.0;

     }

     for(i=0;i<max+1;i++){

       //real part of the initial wave function at t=0

       fact2=2.0*(x-5.0);

       psr[i][0] = (Math.cos(k0*x))*Math.exp(-0.5*fact2*fact2);

       //imaginary part of the initial wave function at t=0

       psi[i][0] = (Math.sin(k0*x))*Math.exp(-0.5*fact2*fact2);

       x=x+dx;

     }

   }//if ij



   //propagate solution through time

   for( n=0;n<jj+1;n++){

     if(n==0){

       coormundo(0.0,1.0,max+1,0);

       ejes(0.0,1.0,max+1,0,g);

    }

     //real part of the wave function and probability

     for( i=1;i<max;i++){

       psr[i][1]=psr[i][0] - dt*(psi[i+1][0] + psi[i-1][0]

                 -2.0*psi[i][0])/(2.0*dx*dx);

       p2[i]=psr[i][0]*psr[i][1]+psi[i][0]*psi[i][0];

     }

     //imaginary part of the wave function

     for(i=1;i<max;i++){

       psi[i][1] = psi[i][0]+dt*(psr[i+1][1] + psr[i-1][1]

                     -2.0*psr[i][1])/(2.0*dx*dx);

     }

     //only at certain time instants we want to know



     // the probability

     if(n==jj){

       for(i=1;i<max+1;i++){

         if(i>1){

            peo=(int)(mxx*(i-1)+bxx);

            peyo=(int)(myy*p2[i-1]+byy);

            pex=(int)(mxx*i+bxx);

            peye=(int)(myy*p2[i]+byy);

            g.drawLine(peo,peyo,pex,peye);

          }

       }

     }

     // new iterations are now the old ones

     for(i=1;i<max+1;i++){

       psi[i][0]=psi[i][1];

       psr[i][0]=psr[i][1];

     }

  }

 }



  public void init()

 {

   psr=new double[751][2];

   psi=new double[751][2];

   //psr=new double[501][2];

   //psi=new double[501][2];

   offScreenImage=createImage(size().width,size().height);

   //using.java 1.1 p 554

   p2=new double[751];

  jj=1;

  pi=3.14159265358979323846;

  max=750;

  k0=8.0*pi;

  dx=0.02;

 }

 public void paint(Graphics g){

    Equation(g,jj);

    jj=30;

 }



}