!--------------------------------------------------------------------------
   !---------------------------- gradient ----------------------------------
   DO l = ll_begin, ll_end
      !DIR$ SIMD
      DO ij=ij_begin_ext, ij_end_ext
         grad(ij+u_right,l) = ne_right*(b(ij+t_right,l)-b(ij,l))
         grad(ij+u_lup,l) = ne_lup*(b(ij+t_lup,l)-b(ij,l))
         grad(ij+u_ldown,l) = ne_ldown*(b(ij+t_ldown,l)-b(ij,l))
      END DO
   END DO
   !---------------------------- gradient ----------------------------------
   !--------------------------------------------------------------------------