// 2D Ising with Metropolis algorithm,  Evgeny Demidov  23 Oct 2006
  // based on Harvey Gould and Jan Tobochnik sources   sip.clarku.edu
  import java.awt.*;
  import java.awt.event.*;
  public class applet-math-IsingM1 extends java.applet.Applet implements MouseListener,
   MouseMotionListener, ItemListener, KeyListener, ActionListener, Runnable {
    Thread thCycle;
    int L = 50,L1, M, E, d, w, hd, hBut = 30, border = 0, nInit = 0,
      it, Mi[], Ei[], spin[][];
    double T = 2.269, avM, avMM, avE, avEE,  wi[];
    boolean painted = false, bCycle = false;
    long generTime;
    float flM, flE;
    Image buffImage;     Graphics buffGraphics;
    Choice chL,chBorder,chInit;
    Label  lbL,lbT,lbBorder,lbInit;    TextField tfT;
    Button   btRun, btClear, btPrint;
  public void init(){
    w = getSize().width - 200 - 10;
    spin = new int[w+2][w+2];
    Mi = new int[w];  Ei = new int[w];
    String s=getParameter("L"); if (s != null) L = Integer.parseInt(s);
    d = w/L;  hd = w-d; L1 = L+1;
    s=getParameter("T"); if (s != null) T = Double.valueOf(s).doubleValue();
    s=getParameter("Init"); if (s != null) nInit = Integer.parseInt(s);
    wi = new double[5];  wi[0] = 1.;
    for (int i = 1; i < 5; i++) wi[i] = Math.exp(-2*i/T);
    setup();
    lbT = new Label("T", Label.RIGHT);  add(lbT);
    tfT = new TextField( "" + (float)T, 5);  add(tfT);
    tfT.addKeyListener(this);
    lbL = new Label("L", Label.RIGHT);  add(lbL);
    chL = new Choice();
    if (w == 400){
     chL.addItem("20");
     for (int i = 0, l = 50; i < 4; i++){
      chL.addItem(Integer.toString(l));  l *= 2;}}
    else
     for (int i = 0, l = 20; i < 6; i++){
      chL.addItem(Integer.toString(l));  l *= 2;};
    chL.select(""+L);  chL.addItemListener(this);  add(chL);
    lbBorder = new Label("border", Label.RIGHT);  add(lbBorder);
    chBorder = new Choice();
    chBorder.addItem("free"); chBorder.addItem(" +1 ");
    chBorder.select(border);
    chBorder.addItemListener(this);  add(chBorder);
    lbInit = new Label("init", Label.RIGHT);  add(lbInit);
    chInit = new Choice();
    chInit.addItem(" -1 "); chInit.addItem("rand"); chInit.addItem(" +1 ");
    chInit.select(nInit + 1);
    chInit.addItemListener(this);  add(chInit);
    btRun = new Button("Run ");  btRun.addActionListener(this);  add(btRun);
    btClear = new Button("Clear");   btClear.addActionListener(this);
    add(btClear);
    btPrint = new Button("Print");   btPrint.addActionListener(this);
    add(btPrint);
    buffImage = createImage(w+210, w);   buffGraphics = buffImage.getGraphics();
    addMouseListener(this);  addMouseMotionListener(this);
  }
  public void setup(){
    it = 0;
    for (int i = 0; i < w; i++) Mi[i] = Ei[i] = w;
    for (int i = 0; i <= L1; i++)
      spin[0][i] = spin[L1][i] = spin[i][0] = spin[i][L1] = border;
    M = E = it = 0;
    for (int i = 1; i < L1; i++)
     for (int j = 1; j < L1; j++){
      int s;
      if (nInit != 0) s = spin[i][j] = nInit;
      else if (Math.random() > .5) s = spin[i][j] = 1; else s = spin[i][j] = -1;
      M += s; E -= s*(spin[i-1][j] + spin[i][j-1]);}
    for (int i = 1; i < L1; i++){
      E -= spin[i][L]*spin[i][L1];  E -= spin[L][i]*spin[L1][i];}
    M /= 2;  E /= 2;
  }
  public void destroy(){
    removeMouseListener(this);  removeMouseMotionListener(this);
  }
  public void run() {
    while(true) {
      if ( Thread.currentThread() != thCycle ) return;
      MC();
      painted = false;
      repaint();
      try {  Thread.sleep( 20 );
      } catch (InterruptedException e) {}
    }
  }
  public void stop(){  thCycle = null; }
  public void actionPerformed(ActionEvent e){
    if ( e.getActionCommand().equals("Clear") ){
      for (int i = 0; i < w; i++) Mi[i] = Ei[i] = w;
      it = 0;  avM = avMM = avE = avEE = 0.;
      showStatus( "it="+ it);}
    else if ( e.getActionCommand().equals("Print") ){
      double Mt = avM/it, Et = avE/it, n = L*L;
      showStatus( "T="+ (float)T +"  M="+ (float)Mt +
       "  x="+ (float)(n*(avMM/it - Mt*Mt)/T) +"  E="+ (float)Et +
       "  C="+ (float)(n*(avEE/it - Et*Et)/(T*T)) +"  it="+ it );
      System.out.println( ""+ (float)T +"  "+ (float)Mt +
       "  "+ (float)(n*(avMM/it - Mt*Mt)/T) +"  "+ (float)Et +
       "  "+ (float)(n*(avEE/it - Et*Et)/(T*T)) );}
    else{
      if (bCycle){
        bCycle = false;  btRun.setLabel("Run "); thCycle = null;}
      else { bCycle = true;  btRun.setLabel("Stop");
        thCycle = new Thread(this); thCycle.start();}}
  }
  public void mouseClicked(MouseEvent e){}       // event handling
  public void mousePressed(MouseEvent e) {
    if( e.getX() < w){
      MC();
      painted = false;
      repaint();}
    e.consume();
  }
  public void mouseReleased(MouseEvent e){}
  public void mouseEntered(MouseEvent e) {}
  public void mouseExited(MouseEvent e)  {}
  public void mouseMoved(MouseEvent e) {}
  public void mouseDragged(MouseEvent e) {
    if( e.getX() > w){
      T = 6. - (e.getY() - 30)*6./w;
      for (int i = 1; i < 5; i++) wi[i] = Math.exp(-2*i/T);
      tfT.setText(""+(float)T);
      painted = false;
      repaint();}
    e.consume();
  }
  public void keyTyped(KeyEvent e){}
  public void keyPressed(KeyEvent e){}
  public void keyReleased(KeyEvent e){
    final int keyEnter = 10;
    if (e.getKeyCode() == keyEnter){
      try{ T = Double.valueOf(tfT.getText()).doubleValue();
      }catch(NumberFormatException ne){}
      for (int i = 1; i < 5; i++) wi[i] = Math.exp(-2*i/T);
      painted = false;
      repaint();
    }
    e.consume();
  }
  public void itemStateChanged(ItemEvent e){
    Object src = e.getSource();
    if (src == chL){
     L = Integer.parseInt(chL.getSelectedItem());
     d = w/L;  hd = w-d; L1 = L+1;}
    if (src == chBorder) border = chBorder.getSelectedIndex();
    if (src == chInit) nInit = chInit.getSelectedIndex() - 1;
    setup();
    painted = false;
    repaint();
  }
  public void MC(){
    generTime = System.currentTimeMillis();
    for (int i = 1; i < L1; i++)
     for (int j = 1; j < L1; j++){
       int sum = spin[i][j]*
         (spin[i][j+1] + spin[i][j-1] + spin[i+1][j] + spin[i-1][j]);
       if ( (sum <= 0)||(Math.random() < wi[sum]) ){
         int s = spin[i][j] = -spin[i][j];
         M += s;  E += sum;}}
    flM = 2*(float)M/(L*L);  flE = 2*(float)E/(L1*L1);
    avM += flM; avMM += flM*flM;  avE += flE; avEE += flE*flE;
    Mi[it % w] = w + (int)(100*(flM + 1));
    Ei[it % w] = w + (int)(50*(flE + 2));   it++;
    generTime = System.currentTimeMillis() - generTime;
  }
  public void paint(Graphics g){
   if ( !painted ){
    buffGraphics.setColor(Color.white);
    buffGraphics.fillRect(0, 0, w+200, w);
    buffGraphics.setColor(Color.black);
    for (int i = 0; i < L; i++)
     for (int j = 0; j < L; j++)
       if (spin[i+1][j+1] < 0) buffGraphics.fillRect(j*d,hd-i*d, d,d);
    buffGraphics.setColor(Color.lightGray);
    for (int i = 0; i < 200; i += 20)
      buffGraphics.drawLine(w+i, 0, w+i, w);
    buffGraphics.setColor(Color.gray);
    buffGraphics.drawLine(w+100, 0, w+100, w);
    buffGraphics.setColor(Color.red);
    for (int i = 0; i < w; i++)
     buffGraphics.drawLine(Mi[i], i, Mi[i], i);
    buffGraphics.setColor(Color.blue);
    for (int i = 0; i < w; i++)
     buffGraphics.drawLine(Ei[i], i, Ei[i], i);
    int Ti = (int)((1. - T/6.)*w);
    buffGraphics.setColor(Color.red);
    buffGraphics.fillRect(w+200, Ti, 10, w-Ti);
    buffGraphics.setColor(Color.white);
    buffGraphics.fillRect(w+200, 0, 10, Ti);
    buffGraphics.setColor(Color.black);
    buffGraphics.fillRect(w+200, (int)((1. - 2.269/6.)*w)-1, 10, 3);
    painted = true;}
   g.drawImage(buffImage, 0, hBut, this);
   showStatus( "T="+ (float)T +"  it="+ it +"  M="+ flM +
    "  E="+ flE +"  t="+ generTime +"ms ");
  }
  public void update(Graphics g){ paint(g); }
  }