/* Initial conditions for the temperature of a bar
  vary as 100 sin(2pi x)   for 0<= x <=1 Color code:
  red for positive temperatures, blue for negative, black for 0 T*/

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

public class Barsin2 extends Applet implements Runnable {
  Thread runstring;
  private Image offScreenImage;
  double mxx,bxx,myy,byy;
  int jj,Flag,firstime;

 public Barsin2() //to initialize Flag
  {
    setFlag(0);
  }
  public void setFlag(int fl)
  {
     Flag=fl;    //Flag 0 do not begin string motion, 1 yes
  }

  public void start()
  {
   if(runstring==null)
   {
     if(Flag==0){
       runstring=new Thread(this);
       runstring.start();
     }
    }
  }
    public void stop()
  { //stops motion

     if(runstring != null){
       runstring.stop();
       System.gc();
       runstring=null;
     }
  }
  public void run()
  {
    while(true){
      repaint();
      try{ Thread.sleep(300);
      }
      catch(InterruptedException e){ }
    }
  }
  public void init()
  {
     offScreenImage=createImage(size().width,size().height);
     add(new Button("Stop"));
     add(new Button("Start"));
     jj=1;
     Flag=0;
     firstime=0;
  }
  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)
  {
    //Plot the axis
    //  0.0 to 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;
  //tics in vertical axis
  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-30,ydiv+5);
    g.drawString("Temperature",xpi,yps-30);
  }

  }

  public void Barsin2plot(Graphics g)
  {
    double ro,sph,diffk,cons,dx,dt,el,xx;
    double thk,divi,u[][],pi;
    int j,ngrid;
    int nmaxi,k,i,il,km,ii;
    int peo,peyo,pex,peye,tone;
    ngrid=101;
    u=new double[101][2];
    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,-120.0);
    }
    /*the bar is divided in 100 parts (divi)      */
    divi=100.0;
    cons=0.1;
    dx=el/divi;
    dt=cons*dx*dx/diffk ;
    pi=3.14159265358979323846;
    // At t=0 ( j=1) the temperature distribution
    for(i=0;i<100;i++){
        xx=0.01*i;
        u[i][0]=100.0*Math.sin(2.0*pi*xx);
     }
     //in i=1 and i=101 (ends) U=0 for all times
      for(j=0;j<2;j++){
        u[0][j]=0.0;
        u[100][j]=0.0;
      }
      nmaxi=20000;
      //loop over time
      //loop 40 over space, end points not included (known)
      for(k=1;k<jj+1;k++){
        for(i=1;i<100;i++){
           u[i][1]=u[i][0] + cons*(u[i+1][0]+u[i-1][0]-2.0*u[i][0]);
        }
        if(k==jj)
        {
          ejes(0,100.0,100.0,-100.0,g);
          for(j=0;j<100;j++){
            tone=(int)(2.55*u[j][1]);
            tone=Math.abs(tone);
            Color redi=new Color(tone,0,0);
            g.setColor(redi);
            if(u[j][1]<0){
             Color bluy=new Color(0,0,tone);
              g.setColor(bluy);
            }
            g.drawRect(49+5*j,30,5,25);
            g.fillRect(49+5*j,30,5,25);
          }
          for(i=0; i<101; i++)
         { 
            if(i>0){
              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
      }
      for(i=1;i<100;i++)u[i][0]=u[i][1];
      } //for k
    } //rutine

  public void paint(Graphics g){
    Barsin2plot(g);
    if(Flag==1){
     jj=jj+50;
    }
 }

 public boolean action(Event ev, Object whataction)
 {
   if(!(ev.target instanceof Button))
   {
     return false;
   }
   String buttonLabel=(String) whataction;
   if(buttonLabel=="Start")
   { firstime=0;
     jj=1; //To start from initial conditions
     setFlag(1);
     runstring.start();
   }
   if(buttonLabel=="Stop")
   { //really means pause, it doesnït kill applet
     setFlag(0);
     firstime=1;
   }
   return true;
 }
}//class