program parabola
      real x(101),y(101),xpt(5),ypt(5)
      integer pgopen
      if(pgopen('/xwin')<=0) stop
      
      dx = (5.0-0.0)/100
      do i=1,101
        x(i)= (i-1)*dx
        y(i)= x(i)**2
      enddo
      do i=1,5
        xpt(i)=i
        ypt(i)=i*i
      enddo

      call pgenv(0.0,4.0,0.0,20.0,0,0)
      call pgline(101,x,y)
      call pgpt(5,xpt,ypt,9)

      call pgclos
      end