/*
 * ftjn.java - revised 26 Feb 10 - width 401, height 301
 * @author jackord@kw.igs.net
 * restricted 3-body problem:
 *   (1) locating equilibrium sites in the rotating frame using a color
 *       plot of effective potential
 *   (2) testing the stability of orbits at the Trojan and saddle point sites
 */

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

public class ftjn extends Applet 
                    implements ActionListener {
  int kk=0;                                            // Declarations
  int x0, y0, imax;                                    // Global
  double x1, x2, m1, m2, w, w2, dt;                    //   variables
  String b1s = "Tro"; Button b1 = new Button(b1s);
  String b2s = "Sad"; Button b2 = new Button(b2s);
  Color col[]={ Color.blue, Color.cyan, Color.red, Color.yellow, Color.green, Color.magenta };
  Choice ch=new Choice();

  public void init() {                                 
    setBackground(new Color(211, 211, 211));
    ch.addItem("M/m=9"); ch.addItem("M/m=19");
    ch.addItem("M/m=29"); ch.addItem("M/m=99");
    ch.addItem("Jupiter"); ch.addItem("Earth");
    add(ch); add(b1); add(b2);
    b1.addActionListener(this);
    b2.addActionListener(this);
    ch.setBackground(getBackground());
  }

  double f(double x) {                                 // Force
    double r13, r23;
    r13=Math.pow((x-x1)*(x-x1), 1.5); r23=Math.pow((x-x2)*(x-x2), 1.5);
    return w2*(x-x0)+m1*(x1-x)/r13+m2*(x2-x)/r23;
  }

  public void orbit(double x, double y, Graphics g) {  // Plot orbit
    double r13, r23, vx, vy, dvx, dvy;
    int xa, ya, xb, yb;
    r13=Math.pow((x-x1)*(x-x1)+(y-y0)*(y-y0), 1.5);
    r23=Math.pow((x-x2)*(x-x2)+(y-y0)*(y-y0), 1.5);
    dvx=(w2*(x-x0)-m1*(x-x1)/r13-m2*(x-x2)/r23)*dt;
    dvy=(w2*(y-y0)-m1*(y-y0)/r13-m2*(y-y0)/r23)*dt;
    vx=dvx/2; vy=dvy/2;
    xa=(int)(x); ya=(int)(y);
    for (int i=1; i<=imax; i=i+1) {                    // Feynman loop
      x=x+vx*dt; y=y+vy*dt;
      xb=(int)(x); yb=(int)(y);
      g.drawLine(xa, ya, xb, yb); xa=xb; ya=yb;        // Plot
      r13=Math.pow((x-x1)*(x-x1)+(y-y0)*(y-y0), 1.5);
      r23=Math.pow((x-x2)*(x-x2)+(y-y0)*(y-y0), 1.5);
      dvx=(w2*(x-x0)-2*w*(vy+dvy/2)-m1*(x-x1)/r13-m2*(x-x2)/r23)*dt;
      dvy=(w2*(y-y0)+2*w*(vx+dvx/2)-m1*(y-y0)/r13-m2*(y-y0)/r23)*dt;
      vx=vx+dvx; vy=vy+dvy;
      if ((r13<2197)||(r23<729)) { i=imax; }           // Crash
    }
  }  

  public void paint(Graphics g) {                      // Main Program
    ch.setBounds(3, 3, 70, 20);
    b1.setBounds(3, 277, 30, 20);
    b2.setBounds(36, 277, 30, 20);
    double r1, r2, r13, r23, rr, d, e, f, h, u, x, y, xx, yy;
    int ii, ya, yb, jm, xm;
    double[] m=new double[6];
    double[] c=new double[6];
    double[] a=new double[3];
    double[] b=new double[3];
    m[0]=.1; m[1]=.05; m[2]=1./30.; 
    m[3]=.01; m[4]=.001; m[5]=.000003;
    c[0]=.209; c[1]=.2116; c[2]=.2123; 
    c[3]=.2137; c[4]=.21427; c[5]=.21429;
    x0=200; y0=150; d=140; w2=1/(d*d*d); w=Math.sqrt(w2);
    ii=ch.getSelectedIndex();
    m2=m[ii]; m1=1-m2; x1=x0-m2*d; x2=x0+m1*d;         // Site M and m
    a[0]=0; b[0]=x1-13; a[1]=x0; b[1]=x2-9; a[2]=x2+9; b[2]=400;
    xx=x1+d/2; yy=y0-d*Math.sqrt(3)/2;                 // Site Trojans
    g.setColor(Color.black);                           // Initial screen
    g.drawRect(0, 0, 400, 300);
    g.setColor(Color.black);
    g.fillArc((int)(x1+.5)-14, y0-14, 28, 28, 0, 360);
    g.fillArc((int)(x2+.5)-10, y0-10, 20, 20, 0, 360);
    if (kk>0) {                                        
      long tt=System.currentTimeMillis(); int del=8;
      for (int i=1; i<=399; i=i+1) {                   // Scan the screen
        for (int j=0; j<=149; j=j+1) {
          rr=(i-x0)*(i-x0)+j*j;
          r1=Math.sqrt((i-x1)*(i-x1)+j*j);
          r2=Math.sqrt((i-x2)*(i-x2)+j*j);
          if ((r1<=13)||(r2<=9)) {
            g.setColor(Color.black);
          }
          else {
            u=w2*rr/2+m1/r1+m2/r2;                     // Effective potential
            g.setColor(col[(int)(c[ii]/u)%6]);
          }
          g.drawLine(i, y0+j, i, y0+j);                // Color pixels
          g.drawLine(i, y0-j, i, y0-j);                //   using symmetry
        }
        while ((tt+i*del)>System.currentTimeMillis()) { }
      }
      if (kk==1) {                                      // Trojan site
        g.setColor(Color.white);
        g.drawLine((int)(x1), (int)(y0), (int)(x2), (int)(y0));
        g.drawLine((int)(x1), (int)(y0), (int)(xx), (int)(yy));
        g.drawLine((int)(x2), (int)(y0), (int)(xx), (int)(yy));
        g.setColor(Color.black);
        tt=System.currentTimeMillis();
        while ((tt+1500)>System.currentTimeMillis()) { }
        dt=5;
        imax=(int)(32*Math.PI/w/dt); if(ii==5) { imax=6*imax; }
        x=xx; y=yy-d/400;
        orbit(x, y, g);
      }
      else {                                           // Saddle points
        g.setColor(Color.white);
        g.drawLine(0, y0, 400, y0);
        ya=0;
        dt=1; imax=(int)(16*Math.PI/w/dt); xm=400; jm=2;
        if (ii==3) { jm=0; imax=2*imax; }
        if (ii>3) {
          xm=180; jm=0; dt=5; imax=5*imax;
          if (ii==5) { dt=50; }
        }
        for (int i=0; i<=xm; i=i+1) {
          r13=Math.pow((i-x1)*(i-x1), 1.5); r23=Math.pow((i-x2)*(i-x2), 1.5);
          yb=(int)(y0+2E5*(w2*(x0-i)+m1*(i-x1)/r13+m2*(i-x2)/r23));
          if ((i>0)&&(ya>0)&&(yb<300)) {
            g.drawLine(i-1, ya, i, yb);                // Plot force
          }
          ya=yb;     
        }
        g.setColor(Color.black);
        for (int j=0; j<=jm; j=j+1) {                  // Three saddle points
          e=a[j]; f=b[j];                              //   if ii<4
          while ((f-e)>.001) {                         // Bisection algorithm
            h=(e+f)/2;
            if (f(h)<0) { e=h; } else { f=h; }
          }
          x=(e+f)/2; y=y0-d/400;
          orbit(x, y, g);
        }
      }
    }
    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();
  }
}