Relative perturbation bound for invariant subspaces of Hermitian matrix

We give a bound for the perturbations of invariant subspaces of a non-singular Hermitian matrix H under relative additive perturbations of H. Such perturbations include the acse when the elements of H are known up to some relative tolerance. Our bound is, in appropriate cases, sharper that the classical bounds, and it generalizes some of the recent relative perturbation results