% discretization

function u=disc(u,uz,ylower,yupper,sn,dis,t)

 ur=yupper-ylower;

 siu=ur/sn;                              % shift interval of y
  
 ul1(dis)=ylower+siu*dis;
 ul2(dis)=ylower+siu*(dis+1);
      if uz(t)<=ul1(dis)
         u(dis,t)=1;
      elseif uz(t)<=ul2(dis)
         u(dis,t)=2;
      else
         u(dis,t)=3;
      end