/*
 * h5c.java - revised 19 Apr 05 - width 401, height 301
 * @author jackord@kw.igs.net
 * the two lowest energy states of a double well (an infinite square well
 *   with a central barrier)
 */

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

public class h5c extends Applet
                 implements ActionListener {
  int kk=0; int first=0; int n;                        // Declarations
  String b1s="State1"; Button b1=new Button(b1s);
  String b2s="State2"; Button b2=new Button(b2s);
                                           
  public void init() {
    setBackground(new Color(211, 211, 211));
    add(b1); b1.addActionListener(this);
    add(b2); b2.addActionListener(this);
  }

  double fey(double e, Graphics g) {                   // Feynman Algorithm
    double y, v, a, c;
    int y1, y2;
    int dx=1; c=Math.PI/400; c=c*c; a=-e*c;
    y=0; v=2; y1=150;
    for (int i=1; i<=n; i=i+1) {
      y=y+v*dx; y2=150-(int)(y);
      g.drawLine(i-1, y1, i, y2); y1=y2;
      if (i==192) { a=(200-e)*c; }
      if (i==209) { a=-e*c; }
      v=v+a*y*dx;
    }
    if (kk==1) { y=v-a*y*dx/2; }
    return y;
  }

  public void paint(Graphics g) {                     
    double e, de, yb, yc, b, c;
    if (first==0) {
      b1.setBounds(25, 200, 60, 20);
      b2.setBounds(105, 200, 60, 20);
      first=1;
    }
    g.setColor(Color.green); g.fillRect(192, 0, 16, 300);
    g.setColor(Color.black); g.drawRect(0, 0, 400, 300);
    g.drawLine(0, 150, 400, 150);
    n=200; g.setColor(Color.blue);
    if (kk>0) {
      b=3.8; c=4.2; de=0.00001;                        // Bisection Algorithm
      yb=fey(b, g); yc=fey(c, g);
      if (yb*yc<0) {
        while ((c-b)>de) {
          e=(b+c)/2;
          if (fey(e, g)*yb>0) { b=e; } else { c=e; }
        }
        g.setColor(Color.red); e=(b+c)/2; n=400; yb=fey(e, g);
        g.drawString("E"+kk+" ="+(float)e, 50, 240);
      }
    }
    kk=0;
  }

  public void actionPerformed(ActionEvent e) {         // Buttons
    String tst;
    tst=e.getActionCommand();
    if (b1s.equals(tst)) { kk=1; }
    if (b2s.equals(tst)) { kk=2; }
    repaint();
  }
}