import java.awt.*;

import java.applet.*;
//copyright 2000 M Paez, U Antioquia, R landau, OSU


public class Strsin extends Applet implements Runnable {

  Thread runstring;

  private Image offScreenImage;

  double mxx,bxx,myy,byy;

  int jj;

  double xi[][],xiw[],ro,ten,vel2,vel;

  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(300);

      }

      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=400;

    maxy=250;

    xxcom=0.15*maxx;

    xxfin=0.75*maxx;

    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,xpd,ypcen);

 }



    public void init()

     {

       double xx,pi;

       int i;

       xi=new double[101][3];

       xiw=new double[101];

       ro=0.010;

       setBackground(Color.black);

       ten=40;

       jj=1;

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

       vel2=ten/ro;

       vel=Math.sqrt(vel2);



      



    }

    

    public void Strplot(Graphics g, int jj)

    { // solves the string partial differential equation

      double  Cons,ten,ro,dx,xx,pi;

      double dt,vel2;

      int peo,peyo,pex,peye;

      int k,m,icoun,il,ip,lam,ll,i,nmax;

      Cons=1.0;

      //initial condition an eigenfunction sin(2pi x/L)

      pi=3.14159265358979323846;

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

         xx=i/100.0;

         xi[i][0]=0.001*Math.sin(2.0*pi*xx);

         xiw[i]=1000.00*xi[i][0];

       }

      if(jj==1){

        dx=1.00/100.00;

        dt= dx/vel;

        nmax=100;

        coormundo(0.0,2.0,100.0,-2.0);



      }

       g.setColor(Color.yellow);

      //the time steps begin here. This is second time step

       ejes(0.0,2.0,100.0,-2.0,g);

      for(i=1;i<100;i++){

        xi[i][1]=xi[i][0]+0.5*(xi[i+1][0]+xi[i-1][0]-2.0*xi[i][0]);

      }

      icoun=0;

      //third time step and following time steps

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

        for(i=1;i<100;i++){

          xi[i][2]=2.0*xi[i][1]-xi[i][0]+Cons*(xi[i+1][1]+xi[i-1][1]

                  -2.0*xi[i][1]);

        }

        for(m=0;m<101;m++){

          //The new iteration in time is now the old

          if(k==0)xiw[m]=1000.00*xi[m][1];

          xi[m][0]=xi[m][1];

          xi[m][1]=xi[m][2];

          if(k>0) xiw[m]=1000.0*xi[m][2];

        }

        // only at every 5 time steps we want data

        // ip=k%5;

        if(k==jj)

        {

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

            {

               if(i>0){

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

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

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

                 peye=(int)(myy*xiw[i]+byy);

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

              }

            }  //for i

         }

       }

   }//rutine

   public void paint(Graphics g)

   {

     Strplot(g,jj);

     jj=jj+10;

   }



}//class