/** Regression **/
import java.awt.*;
import java.applet.*;

public class Regress extends Applet {
  static Point A = new Point(0,0), B = new Point(0,0);
  static Point O = new Point(0,0);
  static Point U = new Point(20,20);
  static int Height, Width;

  static int N = 0;
  final int maxN = 100;
  static double dataPoints[][] = new double[100][2];
  static double meanX = 0.0, meanY = 0.0;
  static double varX = 0.0, varY = 0.0, covXY = 0.0;
  static double slope, intercept;

  static double x, y;
  static boolean clrflg = false;

  public void aw2px(Point t, double x, double v){
    t.x = (int)(   x * (double)U.x + (double)O.x );
    t.y = (int)( - v * (double)U.y + (double)O.y );
  }

  public void init() {
    setBackground(Color.white);
    setForeground(Color.black);

    setLayout(new BorderLayout());
    add("South", new Button("Clear"));
  }

  public void paint(Graphics g) {
    Height = size().height;
    Width  = size().width;
    O.x = Height / 2;
    O.y = Width  / 2;

    draw_coordinate(g);
    draw_data(g);
  }
  
  public void draw_data(Graphics g) {
    int i = 0;
    double x, y;
    Point A = new Point(0,0);
    
    while ( i < N && i < maxN ) {
      g.setColor(Color.blue);
      x = dataPoints[i][0]; y = dataPoints[i][1];
      aw2px(A, x, y);
      g.drawString("("+x+","+y+")", A.x, (int)A.y);
      g.setColor(Color.red);
      g.fillOval(A.x-4, A.y-4, 8, 8);
      i++;
    }
    if ( N > 2 ){
      g.setColor(Color.black);
      aw2px(A, -10.0, -10.0 * slope + intercept);
      aw2px(B,  10.0,  10.0 * slope + intercept);
      g.drawLine(A.x, A.y, B.x, B.y);
      g.drawString("Y="+slope+"X+"+intercept,10,28);
      g.drawString("mean(X)="+meanX+", mean(Y)="+meanY,10,14);
    }
  }

  public void draw_coordinate(Graphics g) {
    g.setColor(Color.blue);
    for (int i = -10; i <= 10; i++) {
      aw2px(A, -10,i);  aw2px(B,  10,i);
      g.drawLine(A.x, A.y, B.x, B.y);
    }
    for (int i = -10; i <= 10; i++) {
      aw2px(A, i,-10);  aw2px(B, i, 10);
      g.drawLine(A.x, A.y, B.x, B.y);
    }

    g.setColor(Color.black);
    aw2px(A,0,-10); aw2px(B,0, 10);
    g.drawLine(A.x, A.y, B.x, B.y);
    aw2px(A,-10,0); aw2px(B,10,0);
    g.drawLine(A.x, A.y, B.x, B.y);
  }

  public void setdata(int x, int y){
    double dx = 0.0, dy = 0.0, dn = 0.0;

    dx = ((double)x - (double)O.x) / (double)U.x;
    dy = - ((double)y - (double)O.y) / (double)U.y;
    dn = (double)N;
    if ( N < maxN ) {
      dataPoints[N][0] = dx;
      dataPoints[N][1] = dy;

      meanX = (meanX * dn + dx)/(dn+1.0);
      meanY = (meanY * dn + dy)/(dn+1.0);
      varX = (varX * dn + (dx - meanX) * (dx - meanX))/(dn+1.0);
      varY = (varY * dn + (dy - meanY) * (dx - meanY))/(dn+1.0);
      covXY = (covXY * dn + (dx - meanX) * (dy - meanY))/(dn+1.0);
      slope = (varX != 0.0) ? (covXY/varX) : 0.0;
      intercept = meanY - slope * meanX;

      this.x = x;
      this.y = y;
      repaint();
      N++;
    }
  }

  public void cleardata(){
    int i=0;

    while ( i <= N ){
      dataPoints[i][0] = 0.0;
      dataPoints[i][1] = 0.0;
      meanX = 0.0; meanY = 0.0;
      varX  = 0.0; varY  = 0.0;
      covXY = 0.0;
      i++;
    }
    N = 0;
  }

  public boolean action(Event ev, Object arg) {
    if (ev.target instanceof Button){
      String l = ((Button)ev.target).getLabel();
      if ( "Clear".equals(l) ){
	cleardata();
        repaint();
      }
    }
    return true;
  }

  public boolean mouseDown( Event evt, int x, int y ) {
    switch( evt.clickCount ) {
    case 1:
      setdata(x, y);
      break;
    }
    return true;
  }

  public boolean handleEvent(Event e) {
    if (e.id == Event.WINDOW_DESTROY) {
      stop();
      destroy();
      System.exit(0);
      return true;
    } else {
      return super.handleEvent(e);
    }
  }

  public static void main(String args[]) {
    PFrame f = new PFrame("Regression");
    Regress regression = new Regress();
    regression.init();
    regression.start();
    f.add("Center", regression);
    f.resize(450, 500);
    f.show();
  }
}

class PFrame extends Frame {
  PFrame(String title) {
    super(title);
  }

  public boolean handleEvent(Event e) {
    if (e.id == Event.WINDOW_DESTROY) {
      dispose();
      System.exit(0);
    }
    return false;
  }
}