/*
	InteractiveCorr applet allows the user to select an
	ordered pair by clicking on a carteasean co-ord grid
	computes R square and least squares regression line
	Version 1.0 - 25 Aug 1999 Chris Thiel <cct@ktb.net>
			
*/

import java.lang.*;
import java.awt.*;
import java.applet.Applet;
import java.awt.Graphics;
import java.awt.Color;
import java.awt.Event;
import java.util.*;

public class icorr extends Applet
{
	int MAX=50;
	int n=0;
	
	String message=null;
	int x[] = new int[MAX];
	int y[] = new int[MAX];
	float xMean, yMean;
    float B0, B1, R_square,Var_x,Var_y;
    double R_Coef;
	int fudge =7;
	int i=0;
	
/*
	Compute is the routine called to compute the Statistical Data
*/	

	public void  compute(){
	// Now calculate regression coeffecients
    	float Sx = 0, Sy =0;
    	float Sxx = 0, Sxy = 0, Syy = 0;
    	

    	for(int i=0; i< n; i++)
    	{
    		
      		Sx += x[i]; 
      		Sy += y[i];
    	}
    	xMean = Sx / n;
    	yMean = Sy / n;
    	for(int i=0; i< n; i++)
    	{
      		Sxx += (x[i]-xMean) * (x[i]-xMean);
      		Sxy += (x[i]-xMean) * (y[i]-yMean);
      		Syy += (y[i]-yMean) * (y[i]-yMean);
    	}
    	B1=Sxy/Sxx;
    	B0 = yMean - B1 * xMean;
    	R_square=(Sxy*Sxy)/(Sxx*Syy);
    	R_Coef = (Sxy)/ Math.sqrt(Sxx*Syy);
	}
	
 	public void clearAll() {
 		n = 0;
 		compute();
 		repaint();
 	}
    
    public void init() {
    	n =0;
		repaint();
	}
	
	public void paint( Graphics g ) {
		 g.setColor(Color.black);
		 for (i=0; i< n; i++){
			g.fillOval(x[i]-2,size().height-y[i]-2, 4,4);
		}
		 g.setColor(Color.magenta);
		g.drawLine(0, (int)(size().height-B0), size().width, 
					(int)(size().height-B1*size().width-B0));
		 g.setColor(Color.black);
		g.drawString( "Number of Pairs:"+n, 25, 15 );
		if (n == MAX-1) {
			g.setColor(Color.red);
			g.drawString( "WARNING: Maximum number of Pairs found", 5,size().height-48);
		 	g.drawString( "subsequent pairs ignored", 35,size().height-36);
		 	}
		g.drawString("Regression Line Equation:",25,30);
		 g.setColor(Color.red);
    	g.drawString("y  = "+B1+" * x + "+B0,25,45);	
    	g.drawString("^",25,43);
    	g.setColor(Color.black);
    	g.drawString("r   = "+R_square,25,60); 
    
    	g.drawString("2",30,57);
    	g.setColor(Color.blue);
    	g.drawString("r  =  "+R_Coef,25,75);
    	 g.setColor(Color.black);
    	g.drawString("_",25,81);
    	g.drawString("_",25,96);
    	
    	g.drawString("x = "+xMean,25, 90);
		g.drawString("y = "+yMean,25, 105);
		if (message != null) {
	    	g.drawString("Error in data: "+message, 10, size().height-24);
	    	g.drawString("Two numbers per line separated by space", 10, size().height-12);

			}
		}// of paint
/*
     * Mouse methods
     */
    public boolean mouseDown(java.awt.Event evt, int x0, int y0) {
      
       x[n]=x0;
       y[n]=size().height-y0;
       n++;
	   if (n == MAX) {
	   		n = MAX-1;
	   		
	   }
	   compute();
       repaint();
       return true;
    }
	
  	
  	
    public boolean mouseMove(java.awt.Event evt, int x, int y) {
     	y = size().height-y;
         getAppletContext().showStatus("Location of mouse: (" + x + ", " + y + ")");
        
         
        return true;
    }

    public void mouseEnter() {
        repaint();
    }

    public void mouseExit() {
       
        repaint();
    }
}//of applet