import java.awt.*;

import java.applet.*;

// copyright, M Paez, 1999, U of Antioquia, r Landau OSU

public class Twobars extends Applet implements Runnable {

  Thread runstring;

  private Image offScreenImage;

  double mxx,bxx,myy,byy;

  int jj;

  public void start()

  {

    if(runstring==null);

    {

     runstring=new Thread(this);

     runstring.start();

    }

  }

  public void stop()

  {

     if(runstring != null){

       runstring.stop();

       runstring=null;

     }

  }

  public void run()

  {

    while(true){

      repaint();

      try{ Thread.sleep(350);

      }

      catch(InterruptedException e){ }

    }

  }

    public void update(Graphics g)

  { //To avoid flicker

    Graphics offScreenGraphics=offScreenImage.getGraphics();

    offScreenGraphics.setColor(getBackground());

    offScreenGraphics.fillRect(0,0,size().width,size().height);

    offScreenGraphics.setColor(g.getColor());

    paint(offScreenGraphics);

    g.drawImage(offScreenImage,0,0,this);

  }

  void coormundo(double xiz,double ysu,double xde,double yinf)

  {

    double maxx,maxy,xxfin,xxcom,yyin,yysu;

    maxx=600;

    maxy=450;

    xxcom=maxx/12.0;

    xxfin=11.0*maxx/12.0;

    yyin=0.8*maxy;

    yysu=0.2*maxy;

    mxx=(xxfin-xxcom)/(xde-xiz);

    bxx=0.5*(xxcom+xxfin-mxx*(xiz+xde));

    myy=(yyin-yysu)/(yinf-ysu);

    byy=0.5*(yysu+yyin-myy*(yinf+ysu));

  }





  void ejes(double xmz,double yms,double xmd,double ymi,Graphics g)

  {

    //Grafica los ejes

    // La entrada esta en coordenadas 0.0 a 1.0

    int i,mp,xpi,xpd,yps,ypi,xdiv,ydiv,ypcen;

    double yincr,xincr,yte;

    //char nhorz[3],nver[15];

    char nver;

    int sig=4;

    ydiv=1;

    xpi=(int)(mxx*xmz+bxx);

    xpd=(int)(mxx*xmd+bxx);

    yps=(int)(myy*yms+byy);

    ypi=(int)(myy*ymi+byy);

    ypcen=(int)byy;

    g.drawLine(xpi,ypcen-30,xpd,ypcen-30);

    g.drawLine(xpi,yps-30,xpi,ypi-30);

    yincr=(ymi-yms)/5.0;

    xincr=(xmd-xmz)/8.0;

  //rayas y marcas en eje vertical

  for (i=0;i<6;i++){

    ydiv=(int)(myy*(yms+yincr*i)+byy-30);

    g.drawLine(xpi-10,ydiv,xpi,ydiv);

    yte=yms+yincr*i;

    if(Math.abs(yte)<0.01)yte=0.0;

    g.drawString(Double.toString(yte),xpi,ydiv-5);

    g.drawString("Temperature",xpi,yps-50);

  }



  }



  public void Twobarsplot(Graphics g, int jj)

  {

    double ro,sph,diffk,cons,dx,dt,el,xx;

    double thk,divi,u[][];

    int j,ngrid;

    int nmaxi,k,i,il,km,ii;

    int peo,peyo,pex,peye,tone;

    ngrid=101;

    u=new double[101][2];

    /* specific heat, thermal conductivity and density for iron

    next three comments. */

    sph=0.217;

    thk=0.49;

    ro=2.7;

    diffk=thk/(sph*ro);

    el=50.0;

    if(jj==1){

      coormundo(0,120.0,100.0,0.0);

    }

    /*the bar is divided in 100 parts (divi)      */

    divi=100.0;

    cons=0.1;

    dx=el/divi;

    dt=cons*dx*dx/diffk ;

    /* At t=0 ( j=0) all points are at 100 C */

    for(i=0;i<ngrid;i++){

      if(i>=50)u[i][0]=100.0;

      if(i<50)u[i][0]=50.0;

    }

    /* in i=0 and i=100 (ends) U=0 for all times*/

    for(j=0;j<2;j++){

      u[0][j]=0.0;

      u[ngrid-1][j]=0.0;

    }

    /*solves numerically the heat partial differential equation

    el,ro,sph,thk,diffk,cons,dx,dt */

    /*  loop over time      */

    for(k=1;k<jj+1;k++){

      /*loop 40 over space, end points not included (they are known)      */

      for(i=1;i<ngrid-1;i++){

        u[i][1]=u[i][0] + cons*(u[i+1][0]+u[i-1][0]-2*u[i][0]);

      }

      /*we want to know the temperatures every 10 000 time steps */

      //il=k%10000;  /* take the modulus */

       if(k==jj)

      {

         ejes(0,100.0,100.0,0.0,g);

         for(j=0;j<100;j++){

           tone=(int)(2.55*u[j][1]);

           Color redi=new Color(tone,0,0);

           g.setColor(redi);

           g.drawRect(49+5*j,330,5,25);

           g.fillRect(49+5*j,330,5,25);

           //g.drawRect(295+5*j,330,5,25);

           //g.fillRect(295+5*j,330,5,25);

         }

         for(i=0; i<101; i++) 

         { 

            if(i>0){

             tone=(int)(2.55*u[i][1]);

           Color redi=new Color(tone,0,0);

           g.setColor(redi);

              peo=(int)(mxx*(i-1)+bxx);

              peyo=(int)(myy*u[i-1][1]+byy-30);

              pex=(int)(mxx*i+bxx);

              peye=(int)(myy*u[i][1]+byy-30);

              g.drawLine(peo,peyo,pex,peye);

            }

         }  //for i

      }

     /*recycle, new values are now old.  */

     for(i=0;i<ngrid-1;i++)u[i][0]=u[i][1];

   }

 }

  public void init()

  {

     offScreenImage=createImage(size().width,size().height);

     jj=1;

  }

  public void paint(Graphics g){

    Twobarsplot(g,jj);

    jj=jj+50;

 }



}