Best approximation with geometric constraints

Abstract

In this paper, we consider a finite family of sets (geometric constraints) \(F_{1}, F_{2},\ldots , F_{r}\) in the Euclidean space \({\mathbb {R}}^n.\) We show under mild conditions on the geometric constraints that the “perturbation property” of the constrained best approximation from a nonempty closed set \(K \cap F\) is characterized by the “convex conical hull intersection property” (CCHIP in short) at a reference feasible point in F. In this case, F is the intersection of the geometric constraints \(F_{1}, F_{2},\ldots , F_{r},\) and K is a nonempty closed convex set in \({\mathbb {R}}^n\) such that \(K \cap F \ne \emptyset .\) We do this by first proving a dual cone characterization of the contingent cone of the set F. Finally, we obtain the “Lagrange multiplier characterizations” of the constrained best approximation. Several examples are given to illustrate and clarify our results.