!     Plotting program for general purpose using postscript
   call init
        call viewport(0.2,0.2,0.8,0.8)
        call xyworld(-0.2,-0.2,1.2,1.2)
        call line(0.5, 0.0, 0.5, 0.02, 0.0, 2.0, 1)
        call line(1.0, 0.0, 1.0, 0.02, 0.0, 2.0,1)
        call line(0.0, 0.5, 0.02, 0.5, 0.0, 2.0,1)
        call line(0.0, 1.0, 0.02, 1.0, 0.0, 2.0,1)
        call arrow(-0.1, 0.0, 1.2, 0.0, 0.02, 0.0, 2.0)
        call arrow(0.0, -0.1, 0.0, 1.2, 0.02, 0.0, 2.0)
        call textx(1.2,-0.02,1,'x')
        call textx(0.5,-0.02,3,'0.5')
        call textx(1.0,-0.02,3,'1.0')
        call texty(-0.02,1.2,1,'y')
        call texty(0.0,0.5,3,'0.5')
        call texty(0.0,1.0,3,'1.0')
        call textx(-0.06,-0.02,1,'O')
        call plotd1
   call fin
  stop
  end
!
  subroutine plotd1
    INTEGER :: m,n,nx,ny,ns
    REAL(4) :: x(100),y(100)
!    call clip(-1.0,-1.0,1.0,1.0)
     call linewidth(1.0)
     call setgray(0.6)
     call linety(1)
      m=10
       do ix=0,m
       do iy=0,m
        x0=0.0+1.0*float(ix)/float(m)
        y0=0.0+1.0*float(iy)/float(m)
        dt=0.05
        dx=1.0; dy=3.0*x0*y0
        ds=sqrt(dx**2+dy**2)
        if(ds.ne.0.0) then
          x1=x0+dx/ds*0.05
          y1=y0+dy/ds*0.05
          call arrow(x0,y0,x1,y1,0.01,0.6,1.0)
       end if
      end do 
      end do
      call stroke
      call newpath
      call setgray(0.4)
      call linewidth(1.2)
      call linety(1)
      n=40
      m=1
       do ix=0,0
       do iy=0,0
       x(0)=0.0
       y(0)=0.1
       dt=0.0128
       call plot(x(0),y(0),3)
        do it=1,2*n
          x(it)= x(it-1)+(1.0)*(dt)
          y(it)= y(it-1)+(3.0*x(it-1)*y(it-1))*(dt)
          call plot(x(it),y(it),2)
        end do
      end do
      end do
  return
  end