epsilon_kvec_vector Function

    real(dp) function epsilon_kvec_vector(k_vec)
        ! and actually this function has to be defined differently for
        ! different type of lattices! TODO!
        ! actually i could get rid of this function and directly call
        ! the dispersion relation of the lattice..
        integer, intent(in) :: k_vec(3)
#ifdef DEBUG_
        character(*), parameter :: this_routine = "epsilon_kvec_vector"
#endif

        ASSERT(associated(lat))

        ! i could save the basic lattice vectors for the lattice or even
        ! store the dispersion relation for each lattice type and call it
        ! with a given k-vector?
        ! change that to only access the cached result of the dispersion
        ! relation

        ! it is necessary to call this function only with k_vectors
        ! within the first BZ!!
        epsilon_kvec_vector = dispersion_rel_cached(lat%get_sym_from_k(k_vec))

    end function epsilon_kvec_vector