/*
 * fspr.java - revised 20 Jan 08 - width 401, height 333
 * @author jackord@kw.igs.net
 * accuracy test of Feynman algorithm
 * mass on an unstretched spring released from rest
 */

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

public class fspr extends Applet 
                   implements ActionListener {
  int kk=0;
  String b1s="Test Accuracy"; Button b1=new Button(b1s);

  public void init() {
    setBackground(new Color(211, 211, 211));           // Light Gray Background
    add(b1); b1.addActionListener(this);
  }


  public void paint(Graphics g) {                      
    g.setColor(Color.black); g.drawRect(0, 32, 400, 300);
    g.setFont(new Font("TimesRoman", Font.PLAIN, 14));
    if (kk>0) {
      double m, k, gr, dt, t, y, v, a, vo, ym, xsc, ysc;
      int x1, y1, x2, y2;
      xsc=400/.83; ysc=300/.23;
      m=2; k=200; gr=9.8; dt=.005; ym=0;
      t=0; y=0; v=0; a=-gr-k*y/m; g.setColor(Color.blue);
      x1=(int)(xsc*(t+.1)); y1=32+(int)(ysc*(.02-y));
      v=v+a*dt/2;
      do {
        vo=v; t=t+dt; y=y+v*dt; a=-gr-k*y/m; v=v+a*dt;
        x2=(int)(xsc*(t+.1)); y2=32+(int)(ysc*(.02-y));
        g.drawLine(x1, y1, x2, y2); x1=x2; y1=y2;
        if ((vo<0) && (v>=0)) { ym=y; }
      } while ((vo<0) || (v>=0));
      t=t+dt/2-v/a;
      g.setColor(Color.black);
      g.drawString("Ymin = "+(float)ym+" (expect "+(float)(-2*m*gr/k)+")", 85, 52);
      g.drawString("Yret = "+(float)y+" (expect 0)", 85, 72);
      g.drawString("Time = "+(float)t+" (expect "+(float)(.2*Math.PI)+")", 85, 92);
    } kk=0;
  }

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

}