Perturbation expansions for singular subspaces of a matrix and for deflating subspaces of a regular matrix pair are derived by using a technique previously described by the author. The perturbation expansions are then used to derive Fréchet derivatives, condition numbers, and rth-order perturbation bounds for the subspaces. Vaccaro's result on second-order perturbation expansions for a special class of singular subspaces can be obtained from a general result of this paper. Besides, new perturbation bounds for singular subspaces and deflating subspaces are derived by applying a general theorem on solution of a system of nonlinear equations. The results of this paper reveal an important fact: Each singular subspace and each deflating subspace have individual perturbation bounds and individual condition numbers.
Mathematics Subject Classification (1991): 65F35
PreliminariesAlthough perturbation bounds for subspaces associated with certain matrix eigenvalue problems and the singular value decomposition of a matrix have been investigated by numerous authors (see, e.g., [1, 4-6, 8-10, 15-18, 21, 23-25]), relatively little attention has been paid to perturbation expansions for the subspaces. Kato [9] gives perturbation series for projections corresponding to invariant subspaces. The author [20] gives perturbation expansions for invariant subspaces. Recently, Vaccaro [22] gives a second-order perturbation expansion for a special class of singular subspaces.