/*
 * fplt.java - revised 20 Jan 08 - width 451, height 393
 * @author jackord@kw.igs.net
 * Euler/Feynman plot
 */

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

public class fplt extends Applet 
                   implements ActionListener {
  int kk=0;
  String b1s="Plot Graph"; 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) {
    double k, m, t, dt, y, dy, v, a;
    int x1, y1, x2, y2;
    g.setFont(new Font("TimesRoman", Font.PLAIN, 16));
    g.setColor(Color.black); g.drawRect(38, 44, 400, 300);
    g.drawString("0", 38-3, 344+20); g.drawString("1", 435, 344+20);
    g.drawString("T", 238, 376);
    g.drawString("0", 38-12, 344+6); g.drawString("2", 38-12, 50);
    g.drawString("Y", 6, 202);
    if (kk>0) {
      k=8; m=2; dt=0.2;
      t=0; y=0; v=2.8; a=-k*y/m;                       // Euler Algorithm
      g.setColor(Color.blue); x1=38; y1=344;
      g.drawString("Euler Algorithm", 220, 212);
      for (int i=1; i<=5; i++) {
        t=t+dt; y=y+v*dt; v=v+a*dt; a=-k*y/m;
        x2=38+(int)(400*t); y2= 344-(int)(150*y);
        g.drawLine(x1, y1, x2, y2); x1=x2; y1=y2;
      }
      t=0; y=0; v=2.8; a=-k*y/m;                       // Feynman Algorithm
      g.setColor(Color.red); x1=38; y1=344;
      g.drawString("Feynman Algorithm", 220, 257);
      v=v+a*dt/2;
      for (int i=1; i<=5; i++) {
        t=t+dt; y=y+v*dt; a=-k*y/m; v=v+a*dt;
        x2=38+(int)(400*t); y2= 344-(int)(150*y);
        g.drawLine(x1, y1, x2, y2); x1=x2; y1=y2;
      }
      t=0; y=0; dt=.005;                               // Analytic Solution
      g.setColor(Color.black); x1=38; y1=344;
      g.drawString("Analytic Solution", 220, 302);
      for (int i=1; i<=200; i++) {
        t=t+dt; y=1.4*Math.sin(2*t);
        x2=38+(int)(400*t); y2= 344-(int)(150*y);
        g.drawLine(x1, y1, x2, y2); x1=x2; y1=y2;
      }
      kk=0;
    }
  }

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

}