for i, mpa, ndims, lv in zip(it.count(), mpas, mpas_ndims, leftvec):
        if ndims == 2:
            leftvec_out[i] = _eig_leftvec_add(lv, mpa.lt[pos], mps_lten)
        elif ndims == 1:
            leftvec_out[i] = _eig_leftvec_add_mps(lv, mpa.lt[pos], mps_lten)