/*
 * mw7.java - revised 23 Apr 07 - width 481, height 241
 * @author jackord@kw.igs.net
 * wave incident (k) on a barrier (ik/n) wave transmitted (k)
 *   (n can have any value, but is set equal to 4 in the example)
 * the barrier width equals the incident wavelength
 * plot shows the modulus of the wavefunction and the probability density
 */

import java.applet.Applet;
import java.awt.*;
import java.awt.event.ActionListener;
import java.awt.event.ActionEvent;

public class mw7 extends Applet
                 implements ActionListener {
  int kk=0;                                            // Declarations
  String b1s="Plot"; Button b1=new Button(b1s);

  public void init() {
    setLayout(new FlowLayout(FlowLayout.LEFT));
    setBackground(new Color(211, 211, 211));
    add(b1);
    b1.addActionListener(this);
  }

  public void paint(Graphics g) {
    int x1, y1, x2, y2;
    double a1, r1, a2, r2, t, n;
    double phase1, phase2, phase3, phase4;
    double a, r, c, s, b, f, dx;
    double [] yy=new double[121];                       
    g.setFont(new Font("TimesRoman", Font.PLAIN, 14));
    g.setColor(Color.black); g.drawRect(0, 0, 480, 240);
    g.drawLine(240, 0, 240, 240); g.drawLine(360, 0, 360, 240);
    if (kk==1) {
      n=4; dx=Math.PI/20; b=2*Math.PI/n;
      c=(Math.exp(-b)+Math.exp(b))/2;                  // Complex arithmetic
      s=(Math.exp(-b)-Math.exp(b))/2;
      f=s*(n-1/n)/2;
      t=1/Math.sqrt(c*c+f*f); phase1=Math.atan2(f, c);
      r1=(n+1/n)*s*t/2; phase2=phase1-Math.PI/2;
      a2=Math.sqrt(1+n*n)*t/2; r2=a2;
      phase4=phase1+Math.atan2(n, 1);
      phase3=phase1-Math.atan2(n, 1);
      a1=100; r1=a1*r1; a2=a1*a2; r2=a1*r2; t=a1*t;    // Amplitudes (finally)
      for (int j=0; j<=80; j=j+1) {
        yy[j]=a1*a1+r1*r1+2*a1*r1*Math.cos(2*j*dx+phase2);
      }
      for (int j=81; j<=120; j=j+1) {
        a=a2*Math.exp((j-120)*dx/n); r=r2*Math.exp((120-j)*dx/n);
        yy[j]=a*a+r*r+2*a2*r2*Math.cos(phase4-phase3);
      }
      g.setColor(Color.blue);
      g.drawString("Probability", 380, 60);
      g.drawString("Amplitude", 400, 75);
      x1=0; y1=240-(int)Math.sqrt(yy[0]);
      for (int j=1; j<=120; j=j+1) {
        x2=3*j; y2=240-(int)(Math.sqrt(yy[j]));
        g.drawLine(x1, y1, x2, y2); x1=x2; y1=y2;
      }
      x2=480; y2=240-(int)t; g.drawLine(x1, y1, x2, y2);
      g.setColor(Color.red);
      g.drawString("Probability", 380, 120);
      g.drawString("Density", 400, 135);
      x1=0; y1=240-(int)(yy[0]/250);
      for (int j=1; j<=120; j=j+1) {
        x2=3*j; y2=240-(int)(yy[j]/250);
        g.drawLine(x1, y1, x2, y2); x1=x2; y1=y2;
      }
      x2=480; y2=240-(int)(t*t/250); g.drawLine(x1, y1, x2, y2);
    }
    kk=0;
  } 

  public void actionPerformed(ActionEvent e) {
    String tst;
    tst=e.getActionCommand();
    if (b1s.equals(tst)) { kk=1; }
    repaint();
  }

}