program plot_para
      real xx(1000),yy(1000)
      i_dummy=pgopen('/xwin')
      call pgenv(-4.0,4.0,0.0,20.0,0,0)
      n=9
      xleft=-4.0
      xright=4.0
      delta_x=(xright-xleft)/(n-1)

      do i=1,n
        x=xleft+(i-1)*delta_x
        y=x**2
        call pgpt(1,x,y,6)
      end do

      m=1000
      dx=(xright-xleft)/(m-1)
      do i=1,m
        xx(i)=xleft+(i-1)*dx
        yy(i)=xx(i)*xx(i)
      end do        
      call pgline(m,xx,yy)
      call pgclos
      end