Alternance Theorems and Chebyshev Splines Approximation

TL;DR

This paper enhances understanding of the alternance property in Chebyshev and spline approximation, offering simpler, constructive proofs and developing new local optimality conditions for free knot polynomial splines.

Contribution

It introduces an original, simplified approach to prove optimality conditions and develops new local optimality criteria for free knot polynomial spline approximation.

Findings

Simplified proofs of optimality conditions for Chebyshev approximation

Constructive algorithms based on the new proofs

New local optimality conditions for free knot spline approximation

Abstract

One of the purposes in this paper is to provide a better understanding of the alternance property which occurs in Chebyshev polynomial approximation and piecewise polynomial approximation problems. In the first part of this paper, we propose an original approach to obtain new proofs of the well known necessary and sufficient optimality conditions. There are two main advantages of this approach. First of all, the proofs are much simpler and easier to understand than the existing proofs. Second, these proofs are constructive and therefore they lead to alternative-based algorithms that can be considered as Remez-type approximation algorithms. In the second part of this paper, we develop new local optimality conditions for free knot polynomial spline approximation. The proofs for free knot approximation are relying on the techniques developed in the first part of this paper.