Geometric Upper Bounds on Rates of Variable-Basis Approximation

In this paper, approximation by linear combinations of an increasing number n of computational units with adjustable parameters (such as perceptrons and radial basis functions) is investigated. Geometric upper bounds on rates of convergence of approximation errors are derived. The bounds depend on certain parameters specific for each function to be approximated. The results are illustrated by examples of values of such parameters in the case of approximation by linear combinations of orthonormal functions.