Given a system of linear equations and inequalities in n variables, a famous result due to A. J. Hoffman (1952) says that the distance of any point in R" to the solution set of this system is bounded above by the product of a positive constant and the absolute residual. We shall discuss explicit representations of this constant in dependence upon the pair of norms used for the estimation. A method for computing a special form of Hoffman constants is proposed. Finally, we use these results in the analysis of Lipsehitz continuity for solutions of parametric quadratic programs.

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