program parabola
      real x(1001), y(1001)
      i_dummy=pgopen('/xwin')
      xmin=-5
      xmax=5
      ymin=-20
      ymax=20
      call pgenv(xmin,xmax,ymin,ymax,0,0)
      dx=(xmax-xmin)/1000
      do i=1,1001
        x(i)=xmin+(i-1)*dx
        y(i)=x(i)*x(i)
      end do
      call pgline(1001,x,y)
      call pgclos
      end