import java.awt.*;
import java.awt.event.*;
import javax.swing.*;

public class Lagrange {
        
    /**
     * Creates a new instance of <code>Lagrange</code>.
     */
    public Lagrange() {
    }
    
    /**
     * @param args the command line arguments
     */
    public static void main(String[] args) {
        new newFrame().init();
    }
}


class newFrame extends JFrame
{
    public void init()  
    {
    	MyPanel hello=new MyPanel();
        getContentPane().add(hello);
        hello.thread.start();

        //以下代碼設置JFrame窗體的外觀
        setSize(400,400);
        setLocation(200,200);
        setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        setVisible(true);
    }
}

class MyPanel extends JPanel implements Runnable
{
    Thread thread;
    
    double xpoint[],ypoint[];
    double x[]={0,10.0,20.0,30.0,40.0,50.0,60.0,70.0,80.0};
    //double y[]={1,1.414214,1.732051,2,2.236068,2.449490,2.645751};
    double y[]={0.0,5,20,45,80,125,180,245,320};
    
    int N=4;
    double t=1.0;
    double s=0.0;
    int num;
    public MyPanel() 
    {
    	xpoint=new double[80];
    	ypoint=new double[80];
        setSize(500, 500);                   
        thread=new Thread(this);
        ////////////////////////以下計算拉格朗日插值
        for(int i=0,k=0;i<80;i++)
        {
        	xpoint[i]=k;
        	k++;
        	s=0.0;
        	for(int m=0;m<N;m++)
        	{
        		t=1.0;
        		for(int n=0;n<N;n++)
        		{
        			if(n!=m)
        			{
        				t=t*(xpoint[i]-x[n])/(x[m]-x[n]);
        			}
        		}
        		s=s+t*y[m];
        	}
        	ypoint[i]=s;
        } 
    }

    public void run()  
    {
    	for(num=2;num<79;num++)      //顯示前num個點
    	{
    		repaint();
    		try{
    			thread.sleep(50);		
    		}
    		catch(InterruptedException e)
    		{
    		}
    	}
    	
    }

     public void paintComponent(Graphics g)   
     {
         g.setColor(Color.white);              
         g.clearRect(0, 0, 400, 440);   

         g.setColor(Color.red);     
         g.drawLine(0, 300, 400, 300);   
         g.drawLine(200, 400, 200, 0); 
         
         g.translate(200,300);
         
         g.setColor(Color.blue);
         
         for(int i=0;i<num;i++)
         {
         	g.drawLine((int)xpoint[i],-(int)(ypoint[i]),(int)xpoint[i+1],-(int)(ypoint[i+1]));
         }
         
         g.setColor(Color.black);
         g.drawString("x[ ]={1.0,2.0,3.0,4.0,5.0,6.0,7.0}",-190,-280);
         g.drawString("y[ ]={0.1,0.4,0.9,1.6,2.5,3.6,4.9}",-190,-260);
         
         g.drawString("拉格朗日插值算法",-180,-200);
         //g.drawString(""+xpoint[54]+"    "+ypoint[54],-180,-50);
     }

}