/*
 * fosd.java - revised 7 Apr 05 - width 481, height 381
 * @author jackord@kw.igs.net
 * the driven damped oscillator (initially at rest at origin)
 *   - sine or square wave driving force
 *   - f/fo equals 1/6, 1/2, 1, 2
 *   - Q equals 1/3, 1, 3, inf
 *   - sine wave analytic solution superposition option (except f=fo, Q=inf)
 */

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

public class fosd extends Applet 
                   implements ActionListener {
  int kk=0;                                            // Declarations
  String b1s="Sine"; Button b1=new Button(b1s);
  String b2s="Square"; Button b2=new Button(b2s);
  Choice cho1=new Choice();
  Choice cho2=new Choice();
  Checkbox ch1= new Checkbox("Anal");

  public void init() {
    setLayout(new FlowLayout(FlowLayout.LEFT));
    cho1.addItem("f=1/6"); cho1.addItem("f=1/2");
    cho1.addItem("f=1");   cho1.addItem("f=2");
    cho2.addItem("Q=1/3"); cho2.addItem("Q=1");
    cho2.addItem("Q=3");   cho2.addItem("Q=inf");
    add(b1); add(b2); add(cho1); add(cho2); add(ch1);
    b1.addActionListener(this);
    b2.addActionListener(this);
    setBackground(new Color(211, 211, 211));           // Light Gray Background
    ch1.setBackground(getBackground());
    cho1.setBackground(getBackground());
    cho2.setBackground(getBackground());
  }

  public void paint(Graphics g) {                      // Paint
    int x1, y1, x2, y2, nf; int n=480;
    double b, c, d, w, wo, w2, wa, wb, rq, dt, t, x, v, dv, r, s, a, a1, a2; 
    double [] bs=new double[5];
    int [] fs=new int[5];
    fs[0]=240; fs[1]=80; fs[2]=40; fs[3]=20;
    bs[0]=3; bs[1]=1; bs[2]=1./3.; bs[3]=0;
    wo=Math.PI/40; w2=wo*wo; c=45; d=w2*c; dt=1;
    if (kk==0) {
      b1.setBounds(5, 5, 55, 20);
      b2.setBounds(65, 5, 55, 20);
      cho1.setBounds(5, 30, 55, 20);
      cho2.setBounds(65, 30, 55, 20);
      ch1.setBounds(125, 5, 55, 20);
      cho1.select(2); cho2.select(1);
    }
    nf=fs[cho1.getSelectedIndex()]; 
    rq=bs[cho2.getSelectedIndex()]; b=wo*rq;
    w=40*wo/nf;
    g.setColor(Color.black);
    g.drawRect(0, 0, 480, 380); g.drawLine(0, 200, 480, 200);
    if (kk==1) {                                       // Sine Wave
      x1=0; y1=200; g.setColor(Color.red);             // Driving Force
      for (int i=1; i<=n; i=i+1) {
        y2=200-(int)(c*Math.sin(w*i*dt)); 
        g.drawLine(x1, y1, i, y2); x1=i; y1=y2;
      }
      t=0; x=0; v=0; dv=0;                             // Feynman algorithm
      g.setColor(Color.blue); x1=0; y1=200;
      for (int i=1; i<=n; i=i+1) {                     // No Half-Step (a=0)
        x=x+v*dt;
        dv=(d*Math.sin(w*i*dt)-b*(v+dv/2)-w2*x)*dt; v=v+dv;
        y2=200-(int)(x); g.drawLine(i-1, y1, i, y2); y1=y2;
      }
      if ((ch1.getState()==true)&&((b>0)||(nf!=40))) { // Analytic solution...
        g.setColor(Color.magenta); y1=200;
        r=w/wo; s=1/r;
        if (nf==40) {
          a=Math.PI/2;
        }
        else {
          a=Math.atan2(rq,(s-r));
        }
        c=c*s/Math.sqrt((s-r)*(s-r)+rq*rq);
        if (rq>2) {                                    // ...overdamped...
          wa=-wo*(rq/2+Math.sqrt(rq*rq/4-1));
          wb=-wo*(rq/2-Math.sqrt(rq*rq/4-1));
          a2=c*(wa*Math.sin(a)+w*Math.cos(a))/(wa-wb);
          a1=c*Math.sin(a)-a2;
          for (int i=1; i<=n; i=i+1) {
            y2=200-(int)(a1*Math.exp(wa*i*dt)+a2*Math.exp(wb*i*dt)+c*Math.sin(w*i*dt-a));
            g.drawLine(i-1, y1, i, y2); y1=y2;
          }
        }
        else {                                         // ...underdamped
          wa=wo*Math.sqrt(1-rq*rq/4);
          a1=c*Math.sin(a); a2=(a1*b/2-w*c*Math.cos(a))/wa;
          for (int i=1; i<=n; i=i+1) {
            y2=200-(int)(Math.exp(-b*i*dt/2)*(a1*Math.cos(wa*i*dt)+a2*Math.sin(wa*i*dt))+c*Math.sin(w*i*dt-a));
            g.drawLine(i-1, y1, i, y2); y1=y2;
          }  
        }
      }
    }
    if (kk==2) {                                       // Square Wave
      g.setColor(Color.red);                           // Driving Force
      g.drawLine(0, 200, 0, 155); g.drawLine(480, 245, 480, 200);
      for (int i=1; i<=n/nf-1; i=i+1) {
        g.drawLine(i*nf, 155, i*nf, 245);
      }
      for (int i=0; i<=n/2/nf-1; i=i+1) {
        x1=i*2*nf; g.drawLine(x1, 155, x1+nf, 155);
        g.drawLine(x1+nf, 245, x1+2*nf, 245);
      }
      g.drawLine(480, 245, 480, 200);
      t=0; x=0; v=0;                                   // Feynman algorithm
      dv=d*dt; v=v+dv/2;                               // Half-Step
      g.setColor(Color.blue); x1=0; y1=200;
      for (int i=0; i<=n/nf-1; i=i+1) {
        for (int j=1; j<=nf; j=j+1) {
          x=x+v*dt;
          dv=(d-b*(v+dv/2)-w2*x)*dt; v=v+dv;
          x2=j+i*nf; y2=200-(int)(x);
          g.drawLine(x1, y1, x2, y2); x1=x2; y1=y2;
        }
        v=v-d*dt; dv=dv-d*dt;                          // Discontinuity corrn
        d=-d;
      }
    }
  }

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