/*
 * fudp.java - updated 7 Apr 05 - width 421, height 301
 * @author jackord@kw.igs.net
 * updated for consistency with Liberty Basic version with eps option
 */

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

public class fudp extends Applet 
                   implements ActionListener {
  int kk=0;                          // Declarations
  double gr, vt;
  String bs="Plot"; Button b=new Button(bs);

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

  double acc(double u) {                               // Newton's Law
    return -(1+u*Math.abs(u)/(vt*vt))*gr;
  }

  public void paint(Graphics g) {
    int x1, y1, x2, y2;                     
    double dt, vret, h, ym, t, y, v, dv;
    g.setColor(Color.black);
    g.drawRect(0, 0, 420, 300);
    if (kk==1) {
      gr=9.8; vt=30; dt=.01; h=0;                      // Feynman Algorithm
      t=0; y=0; v=vt;                                  // ..no air resistance
      g.setColor(Color.red); x1=0; y1=300;
      v=v-gr*dt/2;
      do {
        t=t+dt; y=y+v*dt; v=v-gr*dt;
        x2=(int)(60*t); y2=(int)(6*(50-y));
        g.drawLine(x1, y1, x2, y2); x1=x2; y1=y2;
      } while (y>0);
      t=0; y=0; v=vt;                                  // ..air resistance
      g.setColor(Color.blue); x1=0; y1=300;            
      dv=acc(v)*dt; v=v+dv/2;
      do {
        t=t+dt; y=y+v*dt;
        x2=(int)(60*t); y2=(int)(6*(50-y));
        g.drawLine(x1, y1, x2, y2); x1=x2; y1=y2;
        dv=acc(v+dv/2)*dt; v=v+dv;
        if (((v-dv)>0) && (v<=0)) { h=y; }
      } while (y>0);
      v=v-(.5+y/v/dt)*dv;
      vret=vt/Math.sqrt(2);                            // Analytic V return
      ym=vt*vt*Math.log(2)/2/gr;                       // Analytic Y max
      g.drawString("Initial speed = "+(float)vt, 60, 200);
      g.drawString("Return speed = "+(float)(-v),60, 215);
      g.drawString("Analytic ratio = "+(float)(-v/vret), 60, 230);
      g.drawString("Maximum height = "+(float)h, 60, 260);
      g.drawString("Analytic ratio = "+(float)(h/ym), 60, 275);
    }
    kk=0;
  }

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