We obtain local estimates of the distance to a set defined by equality constraints under assumptions which are weaker than those previously used in the literature. Specifically, we assume that the constraints mapping has a Lipschitzian derivative, and satisfies a certain 2-regularity condition at the point under consideration. This setting directly subsumes the classical regular case and the twice differentiable 2-regular case, for which error bounds are known, but it is significantly richer than either of these two cases. When applied to a certain equation-based reformulation of the nonlinear complementarity problem, our results yield an error bound under an assumption more general than b-regularity. The latter appears to be the weakest assumption under which a local error bound for complementarity problems was previously available. We also discuss an application of our results to the convergence rate analysis of the exterior penalty method for solving irregular problems.Key words. error bound -C 1,1 -mapping -2-regularity -nonlinear complementarity problem -exterior penalty -rate of convergence
Error bounds and their applicationsAmong the most important tools for theoretical and numerical treatment of nonlinear operator equations, optimization problems, variational inequalities, and other related problems, are the so-called error bounds, i.e., upper estimates of the distance to a given set in terms of some residual function. We refer the reader to [31] for a survey of error bounds and their applications. When the set is defined by functional constraints, a typical residual function is some measure of violation of constraints at the given point. When available, error bounds can often be used to obtain a constructive local description of the set under consideration. This description, in turn, plays a central role in the theory of optimality conditions. As another important application of error bounds, we mention development, implementation, and convergence rate analysis of numerical methods for solving optimization and related problems.In this paper, we consider error bounds for sets given by equality constraints. However, it is worth to point out that this setting implicitly includes sets of more general structure, namely those whose constraints can be (equivalently) reformulated into equations. One such example is solution set of the nonlinear complementarity problem, which we shall study in Sect. 3.