/* program for finding the eigen-frequencies of a "guitar" *
 * by using the Numerov- and Schiess-Algorithms            *
 *                                                         *
 * @author: Christoph Federrath                            */

import java.awt.*;
import java.applet.*;
import java.awt.event.*;

public class Guitar extends Applet implements Runnable, ActionListener
{
    private int W=500, H=300, i=0; //window-size, order i
    private double b, bstart=0.0; //eigen-frequency
    private double a=1.0, h=0.01, dbstart=0.1, db;
    private double y, ym1, yp1, x, xp1, xm1, ymax=1, xmax=1;
    private boolean begin = true;
    Thread t;
    Canvas can;
    Button but_next, but_previous;
    private Graphics g;

    public void init()
    {
		setLayout(null);
		can = new Canvas();
		but_next = new Button("Next");
		but_previous = new Button("Previous");
		can.setBackground(Color.white);
		can.setBounds(1,1,W,H);

		but_next.setBounds(W+20,H/2-35,80,30);
        but_previous.setBounds(W+20,H/2+5,80,30);

		add(can); add(but_next); add(but_previous);

		but_next.addActionListener(this);
		but_previous.addActionListener(this);

		g = can.getGraphics();
		g.setColor(Color.blue);
		g.setFont(new Font("Verdana",Font.BOLD,12));

		db=dbstart; b=bstart; //initial values
    }//init()

    public void run()
    {
		try{Thread.sleep(50);} catch(InterruptedException e){}

		g.setColor(Color.blue);
		g.clearRect(0,0,W,H);
		g.drawRect(0,0,W-1,H-1);
		g.drawLine(0,H/2,W,H/2);

		if(begin) //only one time
		{
			begin = false;
			y = 0.01; //y > 0
			i = 1;
			while(db > 1.0e-7)
            {
                if(y > 0)
                {
                    b = b+db;
                    run();
                }
                else
                {
                    b = b-db;
                    db = db/10;
                    b = b+db;
                    run();
        	    }
            }//while
		}
		int px_old, px, py_old, py;

		x=h; ym1=0.0; y=2.0*h; px_old=0; py_old=H/2; yp1=1.0;

		while(x <= 1) //Numerov-algorithm uses function k(x)
    	{
    		xp1 = x+h; xm1 = x-h;
			yp1 = ((2.-5./6.*h*h*k(x))*y-(1.+h*h/12.*k(xm1))*ym1)/(1.+h*h/12.*k(xp1));
    		xm1 = x; x = xp1;
    		ym1 = y; y = yp1;
    		px = (int)(x/xmax*W);
    		py = H/2 -(int)(y/ymax*H/2);

			g.setColor(Color.red);
    		g.drawLine(px_old,py_old,px,py); //draw points

    		px_old = px; py_old = py;
    	}//while

		print(); //print values
    }//run()

    public void actionPerformed(ActionEvent evt)
    {
		if(evt.getActionCommand()==but_next.getActionCommand())
		{
			if(db < 1.0e-7)
			{
                db = dbstart;
                b = b+db;
                run(); //sets a new value for y

                int w;
                w = i%2; //i odd or even
                i++;

                if(w == 0) //i == odd
                {
                    while(db > 1.0e-7) //Schiess-algorithm
                    {
                        if(y > 0)
                        {
                            b = b+db;
                            run();
                        }
                        else
                        {
                            b = b-db;
                            db = db/10;
                            b = b+db;
                            run();
                        }
                    }//while
                }//if i == odd

                if(w == 1) //i == even
                {
                    while(db > 1.0e-7) //Schiess-algorithm
                    {
                        if(y < 0)
                        {
                            b = b+db;
                            run();
                        }
                        else
                        {
                            b = b-db;
                            db = db/10;
                            b = b+db;
                            run();
                        }
                    }//while
                }//if i == even
			}//if db < 10^-7
		}//but_next

    	if(evt.getActionCommand()==but_previous.getActionCommand())
		{
			if(i <= 1){} //only positive values for i are allowed
			else
			{
                db = dbstart;
                b = b-db;
                run(); //sets a new value for y

                int w;
                w = i%2; //i odd or even
                i--;

                if(w == 0) //i == odd
                {
                    while(db > 1.0e-7) //Schiess-algorithm
                    {
                        if(y < 0)
                        {
                            b = b-db;
                            run();
                        }
                        else
                        {
                            b = b+db;
                            db = db/10;
                            b = b-db;
                            run();
                        }
                    }//while
                }//if i == odd

                if(w == 1) //i == even
                {
                    while(db > 1.0e-7) //Schiess-algorithm
                    {
                        if(y > 0)
                        {
                            b = b-db;
                            run();
                        }
                        else
                        {
                            b = b+db;
                            db = db/10;
                            b = b-db;
                            run();
                        }
                    }//while
                }//if i == even
			}//else i > 1
    	}//but_previous
    }//actionPerformed()

	void print()
    {
		g.setColor(Color.blue);
		g.drawString("order:",60,H-30);
		g.drawString("i = "+String.valueOf(i),60,H-10);
		g.drawString("frequency:",W/2-60,H-30);
		g.drawString("b = "+String.valueOf((float)b),W/2-60,H-10);
		g.drawString("accuracy:",W/2+110,H-30);
		g.drawString("db = "+String.valueOf((float)db),W/2+110,H-10);
    }//print()

	double k(double x) //function k(x) in the diff. equ. y''(x)+k(x)*y(x) = 0
	{
		return b*b*Math.PI*Math.PI*(1+a*(Math.sin(Math.PI*x))*(Math.sin(Math.PI*x)));
	}//k(x)

    public void start()
    {
		t = new Thread(this);
    	t.start();
	}//start()
}