EigenvectorDemo2.java

//This applet executes a demo to find the eigenvector of a
//2 dimensional matrix graphically
import java.awt.*;
import java.lang.Integer;
import CoordTransform;
public class EigenvectorDemo2 extends java.applet.Applet {

Float x_coord = null;

//x position of mouse

Float y_coord = null;

//y position of mouse

Float x_vector = null;

//x position of vector

Float y_vector = null;

//y position of vector

int i = 0;

//counter

TextField text1;

//location user enters matrix

TextField text2;

TextField text3;

TextField text4;

Image offscreenImg;

//used for double buffering

Graphics offscreenG;

//used for double buffering

int width;

//width of applet

int height;

//height of applet

CoordTransform c;

//used to transform to user coords

Double matrix[];

int matrixflag = 0;

public void init(){

matrix = new Double[4];

width = this.size().width;

height = this.size().height;

c = new CoordTransform(width,height);

//print text box for entering matrix

setBackground(Color.white);

setLayout(new FlowLayout(FlowLayout.LEFT));

text1 = new TextField(4);

text2 = new TextField(4);

text3 = new TextField(4);

text4 = new TextField(4);

add(new Label("Matrix: "));

add(text1);

add(text2);

add(text3);

add(text4);

//create offscreen buffer

offscreenImg = createImage(width,height);

offscreenG = offscreenImg.getGraphics();

}

public void update(Graphics g){

paint(g);

}

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EigenvectorDemo2.java

public void paint(Graphics g) {

setBackground(Color.white);

//Clear screen

offscreenG.clearRect(0,0,width,height);

//Draw x and y axes

offscreenG.setColor(Color.black);

offscreenG.drawLine(10,height/2,width-20,height/2);

offscreenG.drawString("X",width-13, height/2+4);

offscreenG.drawLine(width/2,20,width/2,height-10);

offscreenG.drawString("Y", width/2-4,13);

//Print out Matrix

if(matrixflag > 3) {

offscreenG.drawString("[ " + matrix[0].toString() + " " +

matrix[1].toString(), 10, 45);

offscreenG.drawString(" " + matrix[2].toString() + " " +

matrix[3].toString() + " ]", 10, 65);

}

//Label axes with hash marks

for(i = 5; i < c.center_x(width-20); i+=5){

offscreenG.drawLine(c.left_x(i),height/2+3,c.left_x(i),

height/2-3);

offscreenG.drawLine(c.left_x(-i),height/2+3,c.left_x(-i),

height/2-3);

//label every 10th coordinate

if(i%10 == 0){

Integer inum = new Integer(i);

Integer inumneg = new Integer(-i);

offscreenG.drawString(inum.toString(),c.left_x(i)-6,

height/2+15);

offscreenG.drawString(inumneg.toString(),c.left_x(-i)-10,

height/2+15);

}

}

for(i=5;i < (int)(height/2-10)/10; i+=5){

offscreenG.drawLine(width/2-3,c.left_y(i),width/2+3,

c.left_y(i));

offscreenG.drawLine(width/2-3,c.left_y(-i),width/2+3,

c.left_y(-i));

//label every 10th coordinate

if(i%10 == 0){

Integer inum = new Integer(i);

Integer inumneg = new Integer(-i);

offscreenG.drawString(inum.toString(),width/2-20,

c.left_y(i)+4);

offscreenG.drawString(inumneg.toString(),width/2-25,

c.left_y(-i)+4);

}

}

//if mouse is over applet, print coordinates

if(x_coord != null)

offscreenG.drawString("Mouse: (" + x_coord + "," + y_coord + ")",

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EigenvectorDemo2.java

10, height-10);

//if mouse has been pressed, draw vector from origin with label

if(x_vector != null){

offscreenG.drawLine(c.left_x(0),c.left_y(0),c.left_x(

x_vector.floatValue()),c.left_y(y_vector.floatValue()));

offscreenG.drawString("Vector: [ " + x_vector + " " + y_vector +

" ]",width-150,height-10);

//if matrix has been entered, draw vector times matrix

if(matrixflag > 3) {

float xmat,ymat;

xmat = x_vector.floatValue()*matrix[0].floatValue()+

y_vector.floatValue()*matrix[2].floatValue();

ymat = x_vector.floatValue()*matrix[1].floatValue()+

y_vector.floatValue()*matrix[3].floatValue();

offscreenG.drawLine(c.left_x(0),c.left_y(0),c.left_x(xmat),

c.left_y(ymat));

}

}

g.drawImage(offscreenImg,0,0,this); //Paint offscreen buffer to screen

}
//if mouse enters applet, set mouse coordinates
public boolean mouseEnter(Event evt, int x, int y) {

x_coord = new Float(c.center_x(x));

y_coord = new Float(c.center_y(y));

repaint();

return true;

}
//if mouse moves in applet, change mouse coordinates
public boolean mouseMove(Event evt, int x, int y) {

x_coord = new Float(c.center_x(x));

y_coord = new Float(c.center_y(y));

repaint();

return true;

}
//if mouse exits applet, stop evaluating current mouse position
public boolean mouseExit(Event evt, int x, int y) {

x_coord = null;

y_coord = null;

repaint();

return true;

}
//if dragging mouse, change vector and mouse coordinates
public boolean mouseDrag(Event evt, int x, int y) {

x_coord = x_vector = new Float(c.center_x(x));

y_coord = y_vector = new Float(c.center_y(y));

repaint();

return true;

}

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EigenvectorDemo2.java

//if user clicks, draw vector and current mouse coordinates

public boolean mouseDown(Event evt, int x, int y) {

x_coord = x_vector = new Float(c.center_x(x));

y_coord = y_vector = new Float(c.center_y(y));

repaint();

return true;

}

//get matrix entries

public boolean action(Event event, Object o) {

//check matrix has been entered

if(event.target instanceof TextField) {

if(event.target == text1) {

matrix[0] = new Double((String)event.arg);

matrixflag++;

}

if(event.target == text2) {

matrix[1] = new Double((String)event.arg);

matrixflag++;

}

if(event.target == text3) {

matrix[2] = new Double((String)event.arg);

matrixflag++;

}

if(event.target == text4) {

matrix[3] = new Double((String)event.arg);

matrixflag++;

}

return true;

}

return false;

}

}

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