import java.awt.*;

import java.applet.*;
//copyright 2000 M Paez, U Antioquia, R landau, OSU
public class Soliton 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(1000);

      }

      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=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)

 {

    //Plots axis

    // 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);

    g.drawLine(xpi,2*yps,xpi,ypi);

 }

  public void init()

 {

  jj=1;

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

 }

 public void paint(Graphics g){

   Equation(g,jj);

   jj=jj+40;

   if(jj>2200)jj=1;

 }



 public void Equation(Graphics g,int jj)

 {

  double ds,dt,mu,eps,tanhy,exp2;

  int i, j, k,max;

  int peo,peye,pex,peyo;

  double a1,a2,a3, fac, time, u[][];

  u=new double[131][3];

  ds= 0.4;                      /* delta x */

  dt= 0.1;                          /* delta t */;

  max= 2000;

  peo=0;

  peyo=0;

  pex=0;

  peye=0;                        /* time steps */

  mu= 0.1;                          /* mu from KdeV equation */

  eps= 0.2;                         /* epsilon from KdeV eq. */

  for(i=0; i<131; i++)                 /* initial wave form */

  {

    exp2=Math.exp(-2*(0.2*ds*i-5.0));

    u[i][0] = 0.5*(1.0 - (1.0-exp2)/(1.0+exp2));

  }

  u[0][1]   =1.;                       /* end points */

  u[0][2]   =1.;

  u[130][1] =0.;

  u[130][2] =0.;

  fac  = mu*dt/(ds*ds*ds);

  time = dt;

  for(i=1; i<130; i++)                 /* first time step */

  {

    if(i==1){

      coormundo(0.0,2.5,131,0.0);

      ejes(0.0,2.5,131,0.0,g);

    }

    a1 = eps*dt*(u[i+1][0] + u[i][0] + u[i-1][0]) / (ds*6.0);

    if((i>1) && (i<129))

    {

       a2 = u[i+2][0] + 2.0*u[i-1][0] - 2.0*u[i+1][0] - u[i-2][0];

    }

    else a2 = u[i-1][0] - u[i+1][0];

    a3 = u[i+1][0]-u[i-1][0];

    u[i][1] = u[i][0] - a1*a3 - fac*a2/3.;

  }

  for(j=1; j<jj+1; j++)                 /* all other time steps */

  {

    time+=dt;

    for(i=1; i<130; i++)

    {

       a1 = eps*dt*(u[i+1][1] + u[i][1] + u[i-1][1]) / (3.0*ds);

       if((i>1) && (i<129))

       {

         a2 = u[i+2][1] + 2.0*u[i-1][1] - 2.0*u[i+1][1] - u[i-2][1];

       }

       else a2 = u[i-1][1] - u[i+1][1];

       a3      = u[i+1][1] - u[i-1][1];

       u[i][2] = u[i][0] - a1*a3 - 2.*fac*a2/3.;

    }

    for(k=0; k<131; k++)              /* move one step ahead */

    {

      u[k][0] = u[k][1];

      u[k][1] = u[k][2];

    }

    //if((j%200)==0)                    /* plot every 200th step */

    if(j==jj)

    {

      for(k=0; k<131; k++)

      {

        if(k>0){

          //fprintf(output, "%f\n", u[k][2]);

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

          peyo=(int)(myy*u[k-1][2]+byy);

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

          peye=(int)(myy*u[k][2]+byy);

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

        }

      }//for k

    }  //if

  }//for j

 } //rutine

}//class