Determining projection constants of univariate polynomial spaces

Minimal Projections and Absolute Projection Constants for Regular Polyhedral Spaces

Let V« [vx,...,vn] be the «-dimensional space of coordinate functions on a set of points ¡cR" where v is the set of vertices of a regular convex polyhedron. In this paper the absolute projection constant of any «-dimensional Banach space E isometrically isomorphic to V c C(v) is computed, examples of which are the well-known cases E = ITM, lln.

Numerical Univariate Polynomial GCD

We formalize the notion of approximate GCD for univariate poly-nomials given with limited accuracy and then address the problem of its computation. Algebraic concepts are applied in order to provide a solid foundation for a numerical approach. We exhibit the limitations of the euclidean algorithm through experiments, show that existing methods only solve part of the problem and assert its worst...

Lipschitz Extension Constants Equal Projection Constants

For a Banach space V we define its Lipschitz extension constant, LE(V ), to be the infimum of the constants c such that for every metric space (Z, ρ), every X ⊂ Z, and every f : X → V , there is an extension, g, of f to Z such that L(g) ≤ cL(f), where L denotes the Lipschitz constant. The basic theorem is that when V is finite-dimensional we have LE(V ) = PC(V ) where PC(V ) is the well-known p...

Numerical Estimation of Projection Constants

Univariate Polynomial Solutions of Nonlinear Polynomial Difference Equations

We study real-polynomial solutions P (x) of difference equations of the formG(P (x−τ1), . . . , P (x− τs)) +G0(x)=0, where τi are real numbers, G(x1, . . . , xs) is a real polynomial of a total degree D ≥ 2, and G0(x) is a polynomial in x. We consider the following problem: given τi, G and G0, find an upper bound on the degree d of a real-polynomial solution P (x), if exists. We reduce this pro...