Optimal Lebesgue constants for least squares polynomial approximation on the (hyper)sphere

Abstract

We investigate the uniform approximation provided by least squares polynomials on the unit Euclidean sphere ${\mathbb{S}}^q$ in ${\mathbb{R}}^{q+1}$, with $q\ge 2$. Like any other polynomial projection, the study concerns the growth, as the degree $n$ tends to infinity, of the associated Lebesgue constant, i.e., of the uniform norm of the least squares operator. If the least squares polynomial of degree $n$ is based on a set of points, which are nodes of a positive weighted quadrature rule of degree of exactness $2n$, then we state two different sufficient conditions for having an optimal Lebesgue constant that increases with $n$ at the minimal projections order. Hence, under our assumptions least squares and hyperinterpolation polynomials provide a comparable approximation with respect to the uniform norm.

17 pages

References in corpus (1)

• Localized linear polynomial operators and quadrature formulas on the sphere