/***************************************************************************
                 module classe zwisd_trazdf_imp.h  -  description
***************************************************************************/
// Mohamed Berrada
// locean-ipsl.upmc, Paris, April 15, 2009
//===========================================================================
//                          methode forward
forward (YREAL x1, YREAL x2)
{ /*	1	from	zdf_avt_avmu_avmv	1  i 	j    k	  t
	2	from	zdf_avt_avmu_avmv	1  i 	j    k+1  t*/   
  /* YS1*/
  /*    2.655954839980409e-18
	6.536998265857578e-17*/
  /* YS2*/
  /*     3.352714069924341e-18
	 7.743459995643917e-17*/
  /* YS3*/
  /*     0
	 0*/

  if(Yt==TU)
    YS1=0.;
  else{
    double  ze3tn = fse3t(Yi,Yj,Yk);
    if(Yi==0 || Yi==NX-1 || Yj==0 || Yj==NY-1 || Yk== NZ-1){
      YS1=0.;
      YS2=0.;
      YS3=0.;
    }
    else{
      
      YS1 = - r2dt * x1/(ze3tn * fse3w(Yi,Yj,Yk  )); //ck*r2dt/e3t
      YS2 = - r2dt * x2/(ze3tn * fse3w(Yi,Yj,Yk+1)); //ck+1*r2dt/e3t
      YS3 = 1. - YS1 - YS2; //r2dt*d(k)/e3t
      //      ! Surface boudary conditions
      if(Yk==0){
	YS1 = 0.e0;
	YS3 = 1. - YS2;
      }
    }
  }
  //
}

//===========================================================================
//                         methode  backward

backward (YREAL x1, YREAL x2)
{
  YJ1I1=0.;     YJ1I2=0.;
  YJ2I1=0.;     YJ2I2=0.;
  YJ3I1=0.;     YJ3I2=0.;
  
  if(Yt!=TU){
    double  ze3tn = fse3t(Yi,Yj,Yk);
    if(Yi==0 || Yi==NX-1 || Yj==0 || Yj==NY-1 || Yk== NZ-1){
      YJ1I1=0.;     YJ1I2=0.;
      YJ2I1=0.;     YJ2I2=0.;
      YJ3I1=0.;     YJ3I2=0.;
    }
    else{
      YJ1I1 = - r2dt /(ze3tn * fse3w(Yi,Yj,Yk  ));
      YJ2I2 = - r2dt /(ze3tn * fse3w(Yi,Yj,Yk+1));
      YJ3I1 = - YJ1I1;
      YJ3I2 = - YJ2I2;
      //      ! Surface boudary conditions
      if(Yk==0){
	YJ1I1 = 0.e0;
	YJ3I1 = 0.;
      }
    }
  }
  //
  
}

  //===========================================================================
//*************************  FIN DU MODULE zwisd_trazdf_imp   *************************