/*
 * large - real-coded lattice gas model 2D
 *
 * coded by Ikeuchi Mitsuru
 * ver 0.0.1   2006.03.12  created
 * ver 0.0.2   2006.03.18  change view menu
 *
 */

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

public class largeRLG2D extends Applet
  implements MouseListener, MouseMotionListener,
    ItemListener, ActionListener, AdjustmentListener, Runnable {

/* -------------------------------------- set global ------ */

  Button bt_reset, bt_startStop;
  Choice ch_view;
  Scrollbar sc_scale;
  Thread th = null;

  Dimension dim;
  Image imgOff;
  Graphics gOff;

  int sleepTime = 50;

  double t = 0.0;
  double dt = 1.0;

  double dx = 1.0;
  double dy = 1.0;

  int Nsx = 640;
  int Nsy = 400;
  double xMax = Nsx*dx;
  double yMax = Nsy*dy;
  int NinCell = 4;

  int dispMode = 2;
  int resetSW = 0;
  int started = 1;
  int incRate = 1;
  double gravity = 0.0;

  double dispScale = (300.0/yMax);
  double viewScale = 1.0;

  int dragSW = 1;
  int dgX, dgY, dgXb, dgYb;
  double xShift = 0.0;
  double yShift = 0.0;

  double viewTheta = -15.0*3.14/180.0;
  double viewFai = -72.0*3.14/180.0;
  double dtheta = 0.0*3.14/180.0;
  double pai = 3.1415926536;
  double cosTh = Math.cos(viewTheta); 
  double sinTh = Math.sin(viewTheta);
  double cosFi = Math.cos(viewFai);
  double sinFi = Math.sin(viewFai);

  int NNp = Nsx*Nsy*NinCell;
  double xx[] = new double [NNp];
  double yy[] = new double [NNp];
  double vx[] = new double [NNp];
  double vy[] = new double [NNp];

  int NNs = 20;
  int section[][][] = new int [Nsx][Nsy][NNs];
  int cellAttribute[][] = new int [Nsx][Nsy];
  double refTemp[] = { 0.0, 0.0, 0.0, 0.0 };

  int vDistribution[][] = new int [200][3];

/* ----------------------------- applet control ------ */

  public void init() {

    resize(630,420);
    setBackground(Color.white);

    dim = getSize();
    imgOff = createImage(dim.width,dim.height);
    gOff = imgOff.getGraphics();

    bt_reset= new Button("reset");
    bt_reset.addActionListener(this);

    bt_startStop= new Button("start/stop");
    bt_startStop.addActionListener(this); 

    ch_view = new Choice();
    ch_view.addItem("sample 8k");
    ch_view.addItem("velocity 8k");
    ch_view.addItem("density");
    ch_view.addItem("flow");
    ch_view.addItem("temperature");
    ch_view.addItem("pressure");
    ch_view.addItem("v space");
    ch_view.addItem("v distr.");
    ch_view.addItemListener(this);
    ch_view.select("density");

    sc_scale= new Scrollbar(Scrollbar.HORIZONTAL,100,10,50,510);
    sc_scale.addAdjustmentListener(this);

    addMouseListener(this);  
    addMouseMotionListener(this);

    setLayout(new BorderLayout());
    Panel pnl = new Panel();
    pnl.setLayout(new GridLayout(1,6,5,0));
    /* pnl.add(new Label("  ")); */
    pnl.add(bt_reset);
    pnl.add(bt_startStop);
    pnl.add(new Label("  "));
    pnl.add(new Label("  "));
    pnl.add(sc_scale);
    pnl.add(ch_view);
    add(pnl,"North");

    setInitialCondition();
  }


  public void start() {
    if (th == null) {
      th = new Thread(this);
      th.start();
    }
  }

  public void stop() {
    if (th != null) {
      th.stop();
      th = null;
    }
  }

  public void itemStateChanged(ItemEvent ev){
    if (ev.getSource() == ch_view) {
      dispMode = ch_view.getSelectedIndex();
    }
  }

  public void actionPerformed(ActionEvent ev){
    if(ev.getSource() == bt_reset){ 
      resetSW = 1;
    } else if (ev.getSource() == bt_startStop){
      if (started==0) {
        started = 1;
      } else {
        started = 0;
      }
    }
  }

  public void adjustmentValueChanged(AdjustmentEvent ev){
    if (ev.getSource() == sc_scale) { 
      viewScale = 0.01*sc_scale.getValue();
    }
  }

  public void mousePressed(MouseEvent ev){ }
  public void mouseReleased(MouseEvent ev){
    dgXb = 0; dgYb = 0;
    dgX = 0; dgY = 0;
  }
  public void mouseClicked(MouseEvent ev){ }
  public void mouseEntered(MouseEvent ev){ } 
  public void mouseExited (MouseEvent ev){ }

  public void mouseMoved  (MouseEvent ev){ }

  public void mouseDragged(MouseEvent ev){
    dgXb = dgX; dgYb = dgY;
    dgX=ev.getX();
    dgY=ev.getY();
    if (dgXb==0 && dgYb==0) {
      dgXb = dgX; dgYb = dgY;
    }
	
    if (dragSW==1) {
      xShift += (1.0/viewScale/dispScale)*(dgX-dgXb);
      yShift += (1.0/viewScale/dispScale)*(dgY-dgYb);
    } else if (dragSW==2) {
      viewTheta += 0.5*3.14/180.0*(dgX-dgXb);
      viewFai += 0.5*3.14/180.0*(dgY-dgYb);
      cosTh = Math.cos(viewTheta); 
      sinTh = Math.sin(viewTheta);
      cosFi = Math.cos(viewFai);
      sinFi = Math.sin(viewFai);
    }
  }

  public void run() {
    while (th != null) {
      try {
        timeEvolution();
        offPaint();
        repaint();
        Thread.sleep(sleepTime);
      } catch (InterruptedException e) { }
    }
  }

  public void update(Graphics g) {
    paint(g);
  }

  public void paint(Graphics g) {
    g.drawImage(imgOff,0,0,this);
  }

/* ----------------------------- offPaint -------------------- */

  void offPaint() {
    int gbx, gby;
    double sc,temp;

    gOff.setColor(Color.white);
    gOff.fillRect(0,0,dim.width,dim.height);

    sc = viewScale*dispScale;
    gbx = 30+(int)(sc*xShift);
    gby = 80+(int)(sc*yShift);

    if (dispMode==0) {
      dragSW = 1;
      ovalPlot(gbx,gby,sc,8000);

    } else if (dispMode==1) {
      dragSW = 1;
      velosityPlot(gbx,gby,sc, 8000, 10.0);

    } else if (dispMode==2) {
      dragSW = 1;
      meanDensityPlot(gbx,gby,sc, 4, 0.5/NinCell);

    } else if (dispMode==3) {
      dragSW = 1;
      meanFlowPlot(gbx,gby,sc, 4, 20.0);

    } else if (dispMode==4) {
      dragSW = 1;
      meanTemperaturePlot(gbx,gby,sc, 4, 1.5);

    } else if (dispMode==5) {
      dragSW = 1;
      meanPressurePlot(gbx,gby,sc, 4, 1.5/NinCell);

    } else if (dispMode==6) {
      dragSW = 1;
      vSpacePlot(30,80,8000);

    } else if (dispMode==7) {
      velocityDistributionPlot(80,100,0.005);
	
    } else if (dispMode==8) {
      ;
	
    }


    gOff.setColor(Color.black);
    gOff.drawString("t="+(int)(t*10.0+0.5)/10.0+" ",630/6*0+10,40);
    if (started==1) {
      gOff.drawString("started",630/6*1+10,40);
    } else {
      gOff.drawString("stopped",630/6*1+10,40);
    }
    gOff.drawString("scale="+(int)(viewScale*100.0+0.5)/100.0+" ",630/6*4+10,40);
    gOff.drawString("view",630/6*5+10,40);

    gOff.setColor(Color.blue);
    temp = systemTemperature();
    gOff.drawString("Box="+Nsx+"x"+Nsy+"",630/6*0+10,60);
    gOff.drawString("N="+NNp+"",630/6*1+10,60);
    gOff.drawString("T="+(int)(temp*1000.0+0.5)/1000.0+"",630/6*2+10,60);
    gOff.drawString("nue="+(int)(viscosityMin(temp)*1000.0+0.5)/1000.0+" ",630/6*3+10,60);
    gOff.drawString("maxNc="+maxSection()+" ",630/6*5+10,60);
    //gOff.drawString("total K="+(float)(totalKineticEnergy())+" ",410,80);

  }


/*------------------------- plot methods -------------------*/

  void ovalPlot(int gx, int gy, double sc,int Nsample) {
    int i,ir,ix,iy;

    drawWaku(gx,gy,sc);
    drawBlock(gx,gy,sc);

    ir = (int)(2*sc+0.5);
    for (i=0; i<Nsample; i++) {
      ix = gx+(int)(xx[i]*sc+0.5);
      iy = gy+(int)(yy[i]*sc+0.5);
      gOff.setColor(Color.getHSBColor(0.66f,0.9f,0.9f));
      gOff.drawOval(ix-ir/2,iy-ir/2, ir, ir);
    }
  }

  void velosityPlot(int gx, int gy, double sc, int Nsample, double mag) {
    int i,ix,iy,ix2,iy2;

    drawWaku(gx,gy,sc);
    drawBlock(gx,gy,sc);

    for (i=0; i<Nsample; i++) {
      ix = gx+(int)(xx[i]*sc+0.5);
      iy = gy+(int)(yy[i]*sc+0.5);
      ix2 = ix+(int)(vx[i]*dt*sc*mag+0.5);
      iy2 = iy+(int)(vy[i]*dt*sc*mag+0.5);
      if (vx[i]>0.0) {
        gOff.setColor(Color.getHSBColor(0.6f,0.9f,0.7f));
      } else {
        gOff.setColor(Color.getHSBColor(0.01f,0.9f,0.7f));
      }
      gOff.drawLine(ix,iy,ix2,iy2);
    }
  }

  void meanFlowPlot(int gx, int gy, double sc, int Ncoarse, double mag) {
    int ic,jc,i,j,ip,k,n,nn,ix,iy,ix2,iy2;
    double mvx, mvy, rho, den;

    drawWaku(gx,gy,sc);
    drawBlock(gx,gy,sc);

    for (ic=0; ic<Nsx; ic+=Ncoarse) {
      for (jc=0; jc<Nsy; jc+=Ncoarse) {
        n = 0;
        mvx = 0.0; mvy = 0.0;
        for (i=ic; i<ic+Ncoarse; i++) {
          for (j=jc; j<jc+Ncoarse; j++) {
            nn = section[i][j][0];
            n += nn;
            for (ip=1; ip<nn; ip++) {
              k = section[i][j][ip];
              mvx += vx[k]; mvy += vy[k];
            }
          }
        }
        mvx = mvx/(n+1.0e-20); mvy = mvy/(n+1.0e-20); 
        rho = n/(1.0*Ncoarse*Ncoarse);
        den = rho/NinCell; if (den>0.9) den = 0.9;

        ix = gx + (int)((ic+Ncoarse/2)*sc);
        iy = gy + (int)((jc+Ncoarse/2)*sc);
        ix2 = ix+(int)(mvx*dt*sc*mag+0.5);
        iy2 = iy+(int)(mvy*dt*sc*mag+0.5);
        if (mvx>=0.0) {
          gOff.setColor(Color.getHSBColor(0.6f,(float)den,0.7f));
        } else {
          gOff.setColor(Color.getHSBColor(0.01f,(float)den,0.7f));
        }
        gOff.drawLine(ix,iy,ix2,iy2);
      }
    }
  }

  void meanDensityPlot(int gx, int gy, double sc, int Ncoarse, double mag) {
    int ic,jc,i,j,ip,k,n,nn,ix,iy,ir;
    double d;

    ir = (int)(Ncoarse*sc+0.999);

    for (ic=0; ic<Nsx; ic+=Ncoarse) {
      for (jc=0; jc<Nsy; jc+=Ncoarse) {
        n = 0;
        for (i=ic; i<ic+Ncoarse; i++) {
          for (j=jc; j<jc+Ncoarse; j++) {
            n += section[i][j][0];
          }
        }
        d = mag*n/(1.0*Ncoarse*Ncoarse); if (d>0.99) d = 0.99;
        ix = gx + (int)(ic*sc);
        iy = gy + (int)(jc*sc);
        gOff.setColor(Color.getHSBColor(0.3f,0.9f,(float)d));
        gOff.fillRect(ix,iy,ir,ir);
      }
    }

    drawWaku(gx,gy,sc);
    drawBlock(gx,gy,sc);
  }


  void meanTemperaturePlot(int gx, int gy, double sc, int Ncoarse, double mag) {
    int ic,jc,i,j,ip,k,n,nn,ix,iy,ir;
    double mvx,mvy,ke,d,den,rho;

    ir = (int)(Ncoarse*sc+0.999);

    for (ic=0; ic<Nsx; ic+=Ncoarse) {
      for (jc=0; jc<Nsy; jc+=Ncoarse) {
        n = 0;
        mvx = 0.0; mvy = 0.0;
        for (i=ic; i<ic+Ncoarse; i++) {
          for (j=jc; j<jc+Ncoarse; j++) {
            nn = section[i][j][0];
            n += nn;
            for (ip=1; ip<nn; ip++) {
              k = section[i][j][ip];
              mvx += vx[k]; mvy += vy[k];
            }
          }
        }
        mvx = mvx/(n+1.0e-20); mvy = mvy/(n+1.0e-20);
        rho = n/(1.0*Ncoarse*Ncoarse);
        den = rho/NinCell; if (den>0.9) den = 0.9;

        ke = 0.0;
        for (i=ic; i<ic+Ncoarse; i++) {
          for (j=jc; j<jc+Ncoarse; j++) {
            nn = section[i][j][0];
            for (ip=1; ip<nn; ip++) {
              k = section[i][j][ip];
              ke += 0.5*((vx[k]-mvx)*(vx[k]-mvx)+(vy[k]-mvy)*(vy[k]-mvy));
            }
          }
        }
        ke = ke/(n+1.0e-20);
        d = mag*ke; if (d>0.99) d = 0.99;
        ix = gx + (int)(ic*sc);
        iy = gy + (int)(jc*sc);
        gOff.setColor(Color.getHSBColor((float)(0.6-0.6*d),(float)den,0.9f));
        gOff.fillRect(ix,iy,ir,ir);
      }
    }

    drawWaku(gx,gy,sc);
    drawBlock(gx,gy,sc);
  }

  void meanPressurePlot(int gx, int gy, double sc, int Ncoarse, double mag) {
    int ic,jc,i,j,ip,k,n,nn,ix,iy,ir;
    double mvx,mvy,ke,rho,d,den;

    ir = (int)(Ncoarse*sc+0.999);

    for (ic=0; ic<Nsx; ic+=Ncoarse) {
      for (jc=0; jc<Nsy; jc+=Ncoarse) {
        n = 0;
        mvx = 0.0; mvy = 0.0;
        for (i=ic; i<ic+Ncoarse; i++) {
          for (j=jc; j<jc+Ncoarse; j++) {
            nn = section[i][j][0];
            n += nn;
            for (ip=1; ip<nn; ip++) {
              k = section[i][j][ip];
              mvx += vx[k]; mvy += vy[k];
            }
          }
        }
        mvx = mvx/(n+1.0e-20); mvy = mvy/(n+1.0e-20);
        rho = n/(1.0*Ncoarse*Ncoarse);
        den = rho/NinCell; if (den>0.9) den = 0.9;

        ke = 0.0;
        for (i=ic; i<ic+Ncoarse; i++) {
          for (j=jc; j<jc+Ncoarse; j++) {
            nn = section[i][j][0];
            for (ip=1; ip<nn; ip++) {
              k = section[i][j][ip];
              ke += 0.5*((vx[k]-mvx)*(vx[k]-mvx)+(vy[k]-mvy)*(vy[k]-mvy));
            }
          }
        }
        ke = ke/(n+1.0e-20);
        d = mag*(ke*rho); if (d>0.99) d = 0.99;
        ix = gx + (int)(ic*sc);
        iy = gy + (int)(jc*sc);
        gOff.setColor(Color.getHSBColor((float)(0.6-0.6*d),(float)den,0.9f));
        gOff.fillRect(ix,iy,ir,ir);
      }
    }

    drawWaku(gx,gy,sc);
    drawBlock(gx,gy,sc);
  }

  void drawBlock(int gx, int gy, double sc) {
    int ix,iy,iss,ca;
    double ss;

    ss = sc*xMax/(double)Nsx;
    iss = (int)(ss+0.999);
	
    for (ix=0; ix<Nsx; ix++) {
      for (iy=0; iy<Nsy; iy++) {
        ca = cellAttribute[ix][iy];
        if (ca>0) {
		  if (refTemp[ca]>0.0) {
            gOff.setColor(Color.getHSBColor(0.85f,0.9f,(float)(0.2+0.8*refTemp[ca])));
          } else {
            gOff.setColor(Color.getHSBColor(0.85f,0.3f,0.9f));
		  }
		  gOff.fillRect(gx+(int)(ss*ix+0.5),gy+(int)(ss*iy+0.5), iss, iss);
        }
      }
    }
  }

  void drawWaku(int gx, int gy, double sc) {
    gOff.setColor(Color.black);
    gOff.drawRect(gx,gy,(int)(sc*xMax+0.5),(int)(sc*yMax+0.5));
  }

/* ---- velocity space plot ---- */

  void vSpacePlot(int gx, int gy, int Nsample) {
    int i,ix,iy,bx,by;
    double mag;

    mag = 50.0;
    bx = (int)(3.0*mag)+gx; by = (int)(3.0*mag)+gy;
    for (i=0; i<Nsample; i++) {
      ix = bx+(int)(vx[i]*mag);
      iy = by+(int)(vy[i]*mag);
      gOff.setColor(Color.getHSBColor(0.66f,0.9f,0.9f));
      gOff.drawLine(ix,iy, ix,iy);
    }
    gOff.setColor(Color.black);
    gOff.drawLine(bx,by-(int)(3.0*mag), bx,by+(int)(3.0*mag));
    gOff.drawLine(bx-(int)(3.0*mag),by, bx+(int)(3.0*mag),by);
  }

/* ---- velocity distribution plot ---- */

  void velocityDistributionPlot(int gx, int gy, double yMag) {
    int i,n1,n2;
    int hoganWidth,hoganHight,xDiv,yDiv;
    double c1,c2,cm;

    setVelocityDistribution();

    hoganWidth = 200; hoganHight = 160; xDiv = 50; yDiv = 80;

    for (i=0; i<200; i++) {
      n1 = (int)(yMag*vDistribution[i][0]);
      if (n1>0) {
        gOff.setColor(Color.lightGray);
        gOff.drawLine(gx+i,gy+hoganHight,gx+i,gy+hoganHight-n1);
      }
    }

    drawHogan(gx,gy,hoganWidth,hoganHight,xDiv,yDiv);
    gOff.setColor(Color.black);
    gOff.drawString("0",gx-5,gy+hoganHight+15);
    gOff.drawString("2",gx+hoganWidth/2-5,gy+hoganHight+15);
    gOff.drawString("4",gx+hoganWidth-5,gy+hoganHight+15);
    gOff.drawString("velocity distribution",gx+20,gy+hoganHight+35);
  }

  void setVelocityDistribution() {
    int i,iv;
    double v;

    for(i=0;i<200;i++) {
      vDistribution[i][0] = 0;
    }

    for(i=0;i<NNp;i++) {
      v = Math.sqrt(vx[i]*vx[i]+vy[i]*vy[i]);
      iv = (int)(50.0*v);
      if (iv<200) {
        vDistribution[iv][0] += 1;
      }
    }
  }

  void drawHogan(int gx, int gy, int hoganWidth, int hoganHight, int xDiv, int yDiv) {
    int i;

    gOff.setColor(Color.gray);
    for (i=0; i<hoganWidth; i+=xDiv) {
      gOff.drawLine(gx+i,gy, gx+i, gy+hoganHight);
    }
    for (i=0; i<hoganHight; i+=yDiv) {
      gOff.drawLine(gx,gy+hoganHight-i, gx+hoganWidth, gy+hoganHight-i);
    }
    gOff.setColor(Color.black);
    gOff.drawRect(gx,gy,hoganWidth,hoganHight);
  }

/*-------------------------- statistics -------- */

  double totalKineticEnergy() {
    int i;
    double tke;

    tke = 0.0;
    for(i=0;i<NNp;i++) {
      tke += 0.5*(vx[i]*vx[i]+vy[i]*vy[i]);
    }
    return( tke );
  }

  double systemTemperature() {
    int i;
    double tke;

    tke = totalKineticEnergy();
    return( tke/NNp );
  }

  double viscosityMin(double temp) {
    int i;
    double rho;

    rho = NNp/(1.0*Nsx*Nsy);
    return( 1.0/12.0+0.5*temp*(1-Math.exp(-rho)/(rho-1+Math.exp(-rho))) );
  }

/*-------------------------- set initial condition -------- */

  void setInitialCondition() {
    int i,ic,jc;
    double x,y;

    t = 0.0;

    for (ic=0; ic<Nsx; ic++) {
      for (jc=0; jc<Nsy; jc++) {
        cellAttribute[ic][jc] = 0;
        if (ic>=Nsx-Nsx/5 && ic<=Nsx-Nsx/5+3 && jc<Nsy/2) {
          cellAttribute[ic][jc] = 1;
        }
      }
    }

    i = 0;
    while ( i<NNp ) {
      x = xMax*Math.random()*0.799;
      y = yMax*Math.random();
      if (cellAttributeAt(x,y)==0) {
        xx[i] = x;
        yy[i] = y;
        vx[i] = 2.0*(Math.random()-0.5);
        vy[i] = 2.0*(Math.random()-0.5);
        i += 1;
      }
    }
  }

/* ----------------------------- timeEvolution -------------- */

  void timeEvolution() {
    int i;

    if (resetSW==1) {
      t = 0.0;
      setInitialCondition();
      started = 0;
      resetSW = 0;
    }
	
    if (started==1) {
      for (i=0; i<incRate; i++) {
        timeStep();
      }
    }
  }

  void timeStep() {
    int i;

    t = t + dt;

    movement();
    collision();
  }

  void movement() {
    int i,ca;
    double rr,r,temp;

    for (i=0; i<NNp; i++) {
      vy[i] += gravity*dt;
      xx[i] += vx[i]*dt;
      yy[i] += vy[i]*dt;

      ca = cellAttributeAt(xx[i],yy[i]);
      if (ca>0) {
        xx[i] -= vx[i]*dt;
        yy[i] -= vy[i]*dt;
        r = 1.0;
        if (refTemp[ca]>0.0) {
          temp = 0.5*(vx[i]*vx[i]+vy[i]*vy[i]);
          r = Math.sqrt(refTemp[ca]/temp)*(1.0-1.0*(Math.random()-0.5));
        } else {
          r = 1.0;
        }
        vx[i] = -r*vx[i];
        vy[i] = -r*vy[i];
      }
    }

    rr = 1.0;
    for (i=0; i<NNp; i++) {
      if (xx[i] < 0.0) { 
        xx[i] = 0.0; vx[i] = -rr*vx[i]; vy[i] = rr*vy[i]; 
      }
      if (xx[i] > xMax) {
        xx[i] = xMax; vx[i] = -rr*vx[i]; vy[i] = rr*vy[i]; 
      }
      if (yy[i] < 0.0) { 
        yy[i] = 0.0; vx[i] = rr*vx[i]; vy[i] = -rr*vy[i]; 
      }
      if (yy[i] > yMax) {
        yy[i] = yMax; vx[i] = rr*vx[i]; vy[i] = -rr*vy[i];
      }
    }
  }

  int cellAttributeAt(double x, double y) {
    int ix,iy;

    ix = (int)(x/dx); if (ix>=Nsx) ix = Nsx-1;
    if (ix<0) ix = 0;
    iy = (int)(y/dy); if (iy>=Nsy) iy = Nsy-1;
    if (iy<0) iy = 0;
    return( cellAttribute[ix][iy] );
  }

  void collision() {
    int ic,jc,nn,ip,k;

    dividingSection();

    for(ic=0;ic<Nsx;ic++) {
      for(jc=0;jc<Nsy;jc++) {
        nn = section[ic][jc][0];
        if (nn>1) {
          if (cellAttribute[ic][jc]==0) {
            collisionInTheCell(ic,jc);
          }
        }
      }
    }
  }

  void collisionInTheCell(int ic, int jc) {
    int i,k,n;
    double cTh,sTh,vxm,vym,vxs,vys;

    cTh = 0.0; sTh = 1.0;
    if (Math.random()<0.5) {
      cTh = 0.0; sTh = -1.0;
    }

    n = section[ic][jc][0];
    vxm = 0.0; vym = 0.0;
    for(i=1;i<=n;i++) {
      k = section[ic][jc][i];
      vxm += vx[k]; vym += vy[k];
    }
    vxm = vxm/n; vym = vym/n;

    for(i=1;i<=n;i++) {
      k = section[ic][jc][i];
      vxs = vx[k]-vxm;
      vys = vy[k]-vym;
      vx[k] = vxm +cTh*vxs +sTh*vys;
      vy[k] = vym -sTh*vxs +cTh*vys;
    }
  }

/*-----  dividing section  -----*/

  void dividingSection() {
    int i,j,ip,iq;

    for(i=0;i<Nsx;i++) {
      for(j=0;j<Nsy;j++) {
        section[i][j][0] = 0;
      }
    }

    for(ip=0;ip<NNp;ip++) {
      i = (int)(Nsx*xx[ip]/xMax); if (i>=Nsx) i = Nsx-1;
      j = (int)(Nsy*yy[ip]/yMax); if (j>=Nsy) j = Nsy-1;
      iq = section[i][j][0]+1;
      if (iq<NNs) {
        section[i][j][0] = iq;
        section[i][j][iq] = ip;
      }
    }
  }

  int maxSection() {
    int i,j,m;

    m = 0;
    for(i=0;i<Nsx;i++) {
      for(j=0;j<Nsy;j++) {
        if (section[i][j][0]>m) m = section[i][j][0];
      }
    }
    return ( m );
  }

/* ----------------------------- end of applet -------------- */

}

/* real-coded lattice gas model 2D
 *
 * method
 *
 * (1) movement
 *  r = r + v*dt
 *
 * (2) collision - all particles collide each other in the same cell
 *  vm = mean v in the cell
 *  vi = vm + rotate(theta)(vi0-vm),  (theta = +-pai/2 : minmum viscosity)
 *
 */