UNIFORM RECIPROCAL APPROXIMATION SUBJECT TO COEFFICIENT CONSTRAINTS

摘要

In this paper best approximation by reciprocals of functions of a subspace Un=span（u1,…,un）satisfying coefficient constraints is considered.We present a characterization ofbest approximations.When（u1,…,un）is a Descartes system an explicit characterization ofbest approximations by equioscillations is given.Existence and uniqueness results are shown.Moreover,the theory is applied to best approximaitons by reciprocals of polynomials.