/*
********************************************************************************
* This applet implements the Cable TV Consumer Preference model presented *
* in Example 2 on p.91 of Larson and Edwards' book, Elementary Linear Algebra, *
* 4th Ed., Houghton-Mifflin (2000) *
* *
* Author : Tom Kimber *
* Date : 2 January 2001 *
********************************************************************************
*/
import java.awt.* ;
import java.applet.* ;
import java.awt.event.* ;
import java.util.* ;
public class tvcpmApplet extends Applet implements ActionListener
{
// --------- Variables ------------
Matrix mat = new Matrix( 3 , 3 , 0.0 ) ;
Matrix vec = new Matrix( 3 , 1 , 0.0 ) ;
int intNumYears ;
// --------- GUI elements ---------
MatrixPanel pnlMatrix = new MatrixPanel( "Transition Matrix:" , mat ) ;
MatrixPanel pnlVector = new MatrixPanel( "Initial States:" , vec ) ;
LabelTextBox txtNumYears = new LabelTextBox( "Number of Years:" ) ;
Label lblActions = new Label( "Actions:" , Label.CENTER ) ;
Button bttnCalculate = new Button( "Calculate" ) ;
Button bttnDefaults = new Button( "Restore Default Inputs" ) ;
Button bttnClear = new Button( "Clear Output" ) ;
Label lblOutput = new Label( "Model Output:" , Label.CENTER ) ;
TextArea txtOutput = new TextArea( "Year | Company A | Company B | No cable \n-----|-----------|-----------|---------" , 20 , 40 ) ;
public void init( )
{ // First layout GUI:
setBackground( Color.cyan ) ;
setLayout( new BorderLayout( ) ) ;
Panel pnlNorth = new Panel( ) ;
pnlNorth.setLayout( new GridLayout( 1 , 3 ) ) ;
pnlNorth.add( pnlMatrix ) ;
pnlNorth.add( pnlVector ) ;
pnlNorth.add( txtNumYears ) ;
add( BorderLayout.NORTH , pnlNorth ) ;
Panel pnlWest = new Panel( ) ;
Panel pnlButtons = new Panel( ) ;
pnlButtons.setLayout( new GridLayout( 4 , 1 ) ) ;
pnlButtons.setFont( new Font( "Monospaced" , Font.PLAIN , 12 ) ) ;
pnlButtons.add( lblActions ) ;
Panel pnlCalculate = new Panel( ) ;
pnlCalculate.add( bttnCalculate ) ;
pnlButtons.add( pnlCalculate ) ;
Panel pnlDefaults = new Panel( ) ;
pnlDefaults.add( bttnDefaults ) ;
pnlButtons.add( pnlDefaults ) ;
Panel pnlClear = new Panel( ) ;
pnlClear.add( bttnClear ) ;
pnlButtons.add( pnlClear ) ;
pnlWest.add( pnlButtons ) ;
add( BorderLayout.WEST , pnlWest ) ;
Panel pnlCenter = new Panel( ) ;
pnlCenter.setLayout( new BorderLayout( ) ) ;
pnlCenter.setFont( new Font( "Monospaced" , Font.PLAIN , 12 ) ) ;
txtOutput.setBackground( Color.white ) ;
pnlCenter.add( BorderLayout.NORTH , lblOutput ) ;
Panel pnlOutputText = new Panel( ) ;
pnlOutputText.add( txtOutput ) ;
pnlCenter.add( BorderLayout.CENTER , pnlOutputText ) ;
add( BorderLayout.CENTER , pnlCenter ) ;
// now set initial input values ...
RestoreDefaultInputs( ) ;
// ... and register the buttons to listen for clicks
bttnCalculate.addActionListener( this ) ;
bttnDefaults.addActionListener( this ) ;
bttnClear.addActionListener( this ) ;
}
public void actionPerformed( ActionEvent e )
{
Object src = e.getSource( ) ;
if ( src == bttnDefaults )
{
RestoreDefaultInputs( ) ;
}
if ( src == bttnCalculate )
{
Calculate( ) ;
}
if ( src == bttnClear )
{
ClearOutput( ) ;
}
}
private void RestoreDefaultInputs( )
{
mat.setEntry( 0 , 0 , .70 ) ;
mat.setEntry( 0 , 1 , .15 ) ;
mat.setEntry( 0 , 2 , .15 ) ;
mat.setEntry( 1 , 0 , .20 ) ;
mat.setEntry( 1 , 1 , .80 ) ;
mat.setEntry( 1 , 2 , .15 ) ;
mat.setEntry( 2 , 0 , .10 ) ;
mat.setEntry( 2 , 1 , .05 ) ;
mat.setEntry( 2 , 2 , .70 ) ;
vec.setEntry( 0 , 0 , 15000 ) ;
vec.setEntry( 1 , 0 , 20000 ) ;
vec.setEntry( 2 , 0 , 65000 ) ;
pnlMatrix.updatePanel( mat ) ;
for ( int i = 0 ; i < vec.getNumRows( ) ; i++ )
{ // display state vector as ints, since these are numbers of people
pnlVector.setValue( i , 0 , ( int ) vec.getEntry( i , 0 ) ) ;
}
txtNumYears.setText( "15" ) ;
}
private void Calculate( )
{
mat.updateFromPanel( pnlMatrix ) ; // get values from panel into matrix
vec.updateFromPanel( pnlVector ) ; // get values from panel into vector
intNumYears = ( int ) txtNumYears.getValue( ) ; // get number of years from text box
if ( isInputOK( ) == false )
{
displayInputErrorMessage( txtOutput ) ;
}
else
{
ClearOutput( ) ;
DisplayOutputLine( 0 ) ; // display year 0 (initial) system state
for ( int i = 1 ; i <= intNumYears ; i++ )
{ // loop to calculate and display
// system state for each year
CalculateNextState( ) ;
DisplayOutputLine( i ) ;
}
}
}
private boolean isInputOK( )
{
int n , m ;
n = mat.getNumRows( ) ;
m = mat.getNumCols( ) ;
// check that entries are positive
for ( int i = 0 ; i < n ; i++ )
{
for ( int j = 0 ; j < m ; j++ )
{
if ( mat.getEntry( i , j ) < 0 )
{
return false ;
}
}
}
// check that column totals = 1
double x = 0 ;
for( int j = 0 ; j < m ; j++ )
{
x = 0 ;
for( int i = 0 ; i < n ; i++ )
{
x = x + mat.getEntry( i , j ) ;
}
if ( Math.abs( x - 1 ) > 0.0001 )
{
return false ;
}
}
// check that the total population doesn't exceed 1,000,000
n = vec.getNumRows( ) ;
x = 0 ;
for ( int i = 0 ; i < n ; i++ )
{
x = x + vec.getEntry( i , 0 ) ;
}
if( x > 1000000.0 )
{
return false ;
}
// check that number of years is <= 100
if( intNumYears > 100 )
{
return false ;
}
// getting here means input OK
return true ;
}
private void displayInputErrorMessage( TextArea x )
{
ClearOutput( ) ;
x.append( "\n*******************\n*** INPUT ERROR ***\n*******************" ) ;
x.append( "\n- Matrix entries should be >= 0" ) ;
x.append( "\n- Column totals should be 1" ) ;
x.append( "\n- Total population should be <= 1000000" ) ;
x.append( "\n- Number of years should be <= 100" ) ;
}
private void DisplayOutputLine( int year )
{
TextArea x = txtOutput ; // just a shorter name ( x ) for the display area ( txtOutput )
int[] vals = new int[ 3 ] ; // array to hold integer values to be displayed
int[] pipePositions = { 6 , 18 , 30 } ; // these are the 'tab' positions where the pipes ( | ) appear in the output display
int line_num = 0 , pos = 0 , width = 0 , num_blanks = 0 ;
line_num = year + 2 ; // the first two lines (i.e., lines 0 and 1 ) of output are for column headings,
// so year i state appears on line i + 2 of text area
width = x.getColumns( ) ;
for ( int i = 0 ; i < vals.length ;i++ )
{ // loop to cast values as ints ( and round ) - for display purposes
vals[ i ] = ( int ) ( vec.getEntry( i , 0 ) + 0.5 ) ;
}
txtOutput.append( "\n" + year ) ;
for ( int i = 0 ; i < vals.length ; i++ )
{ // loop to display values, seperate by pipes, at proper places
// calculations depend on the # of characters in each line
// being equal to the width of the textarea txtOutput
pos = x.getCaretPosition( ) ;
pos = pos - line_num * width ;
num_blanks = pipePositions[ i ] - pos ;
displayBlanks( x , num_blanks ) ;
x.append( "| " + vals[ i ] ) ;
}
// now fill rest of line with blanks, so that # chars in line = width of textarea
pos = x.getCaretPosition( ) ;
pos = pos - line_num * width ;
num_blanks = width - pos ;
displayBlanks( x , num_blanks ) ;
}
private void displayBlanks( TextArea x , int n )
{
for( int i = 0 ; i < n ; i++ )
{
x.append( " " ) ;
}
}
private void CalculateNextState( )
{ // next state vector is matrix times current state vector
vec = MatrixMath.Product( mat , vec ) ;
}
private void ClearOutput( )
{
txtOutput.setText( "Year | Company A | Company B | No cable \n-----|-----------|-----------|---------" ) ;
}
}