// GradientDemo.java
//
// Author: Rahul Simha
// Mar, 2008
//
// An example demonstrating the gradient-descent method.

import javax.swing.*;
import java.awt.*;
import java.awt.event.*;
import java.awt.geom.*;
import java.util.*;
import java.text.*;


public class GradientDemo extends JPanel {

    double alpha = 0.01;          // Algorithm parameter: the stepsize.

    double a=1, b=9;              // Range [a,b]
    double currentX = a;          // x.
    double derivAtCurrentX;       // f'(x)

    // GUI stuff.
    double currentY;              // Used in drawing gradient. 
    double deltaX = 0.1;          // Spacing for sampling points.
    int inset=60;                 // Inset of axes and bounding box.
    double gradOffsetX = 1.0;
    


    //////////////////////////////////////////////////////////////////////
    // Gradient method.

    double computef (double x)
    {
        return 5 + (x - 4.71) * (x - 4.71);
    }


    double computefDeriv (double x)
    {
        return 2 * (x - 4.71);
    }
    

    void init ()
    {
        currentX = 1.8;
    }
    

    void nextStep ()
    {
	derivAtCurrentX = computefDeriv (currentX);
        currentX = currentX - alpha * derivAtCurrentX;
	repaint ();
    }



    //////////////////////////////////////////////////////////////////////
    // GUI code.

    public void display ()
    {
        // Make a frame and add this instance (as JPanel).
        JFrame frame = new JFrame ();
        frame.setSize (600, 480);
        Container cPane = frame.getContentPane ();
        cPane.add (makeBottomLayer(), BorderLayout.SOUTH);
        cPane.add (this, BorderLayout.CENTER);
        frame.addWindowListener (new WindowAdapter () {
                public void windowClosing (WindowEvent e) 
                {
                    System.exit(0);
                }
            });
        frame.setVisible (true);
    }
    

    JPanel makeBottomLayer ()
    {
        JPanel panel = new JPanel ();
        JButton resetB = new JButton ("Reset");
        resetB.addActionListener (
            new ActionListener () 
            {
                public void actionPerformed (ActionEvent a)
                {
                    init ();
                }
            }
        );
        panel.add (resetB);
        panel.add (new JLabel ("      "));
        JButton nextB = new JButton ("Next");
        nextB.addActionListener (
            new ActionListener () 
            {
                public void actionPerformed (ActionEvent a)
                {
                    nextStep ();
                }
            }
        );
        panel.add (nextB);
        panel.add (new JLabel ("      "));
        JButton quitB = new JButton ("Quit");
        quitB.addActionListener (
            new ActionListener () 
            {
                public void actionPerformed (ActionEvent a)
                {
                    System.exit (0);
                }
            }
        );
        panel.add (quitB);
        
        return panel;
    }
    


    public void paintComponent (Graphics g)
    {
        super.paintComponent (g);

        // Background.
        Dimension D = this.getSize ();
	g.setColor (Color.white);
	g.fillRect (0,0, D.width, D.height);
        Graphics2D g2 = (Graphics2D) g;
	g.setColor (Color.black);


        // Axes, bounding box.
        g.drawLine (inset,D.height-inset, D.width-inset, D.height-inset);
        g.drawLine (inset,inset, inset,D.height-inset);
        g.drawLine (D.width-inset,inset, D.width-inset,D.height-inset);
        g.drawLine (inset,inset, D.width-inset, inset);

        double w = D.width-2*inset;
        double h = D.height-2*inset;
        double xInterval = w / 10;
        double yInterval = h / 30;

        // X-ticks: 0 to 10 and labels.
        for (int i=1; i<=10; i++) {
            int xTick = (int) (i*xInterval);
            g.drawLine (inset+xTick,D.height-inset-5, inset+xTick,D.height-inset+5);
            g.drawString (""+i, xTick+inset-5, D.height-inset+20);
        }

        // Y-ticks: 0 to 25 and labels.
        for (int i=0; i<=30; i+=3) {
            int yTick = (int) (i*yInterval);
            g.drawLine (inset-5, D.height-yTick-inset, inset+5, D.height-yTick-inset);
            g.drawString (""+i, 1, D.height-yTick-inset);
        }


        // Draw the function.
        g2.setStroke (new BasicStroke(2f));
        g.setColor (Color.blue);
        boolean first = true;
        int prevX=0, prevY=0;
        for (double x=a; x<=b; x+=deltaX) {
            double y = computef (x);
            int plotX = inset + (int) (w*(x-0)/10.0);
            int plotY = D.height - inset - (int) (h*(y-0)/30.0);
            if (first) {
                first = false;
            }
            else {
                g.drawLine(prevX,prevY, plotX,plotY);
            }
            prevX = plotX;
            prevY = plotY;
        }

	// Draw currentX and deriv.
	g.setColor (Color.red);
	int plotX = inset + (int) (w*(currentX-0)/10.0);
	g.drawLine (plotX,D.height-inset-5, plotX,D.height-inset+5);
        // Now gradient.
	if (derivAtCurrentX == 0) {
	    return;
	}
	double x1 = currentX - gradOffsetX;
	double x2 = currentX + gradOffsetX;
	int plotX1 = (int) (inset + (int) (w*(x1-0)/10.0));
	int plotX2 = (int) (inset + (int) (w*(x2-0)/10.0));
	derivAtCurrentX = computefDeriv (currentX);
	currentY = computef (currentX);
	double y1 = currentY + (- gradOffsetX) * derivAtCurrentX;
	double y2 = currentY + (gradOffsetX) * derivAtCurrentX;
	int plotY1 = D.height - inset - (int) (h*(y1-0)/30.0);
	int plotY2 = D.height - inset - (int) (h*(y2-0)/30.0);
	g.setColor (Color.red);
	g2.setStroke (new BasicStroke (1f));
	g.drawLine (plotX1, plotY1, plotX2, plotY2);
    }
    

    public static void main (String[] argv)
    {
        GradientDemo gradientDemo = new GradientDemo ();
        gradientDemo.display ();
    }
    

}