Corona Extendibility and Asymptotic Multiplicativity

We study outer multiplier algebras, C(E)=M(E)/E, also known as corona algebras, and *-homomorphisms A C(E) . We prove in several instances that for all such maps there must exist an extension to a largerC ^* -algebra . The Kasparov Technical Theorem gives one class of examples where . Our theorems apply to subhomogeneous C ^* -algebras, such as , the algebra used in Cuntz's picture of K-theory. Where such an extension theorem exists, there must exist an asymptotic morphism whose restriction to A is equivalent to the identity. We also use extension results to prove closure properties for the collection of C ^*-algebras that have stable relations.     

Extendibility of spherical matrix distributions

We investigate the structure of distributions for matrices which can be embedded in arbitrarily large matrices whose distributions have properties of invariance under orthogonal rotations.     

Extendibility of homogeneous polynomials on Banach spaces

We study the -homogeneous polynomials on a Banach space that can be extended to any space containing . We show that there is an upper bound on the norm of the extension. We construct a predual for the space of all extendible -homogeneous polynomials on and we characterize the extendible 2-homogeneous polynomials on when is a Hilbert space, an -space or an -space.

     

Extendibility of bilinear forms on banach sequence spaces

We study Hahn-Banach extensions of multilinear forms defined on Banach sequence spaces. We characterize c ₀ in terms of extension of bilinear forms, and describe the Banach sequence spaces in which every bilinear form admits extensions to any superspace.     

Continuous Extendibility of Solutions of the Third Problem for the Laplace Equation

A necessary and sufficient condition for the continuous extendibility of a solution of the third problem for the Laplace equation is given.     

Regularity of Irregular Subdivision

We study the smoothness of the limit function for one-dimensional unequally spaced interpolating subdivision schemes. The new grid points introduced at every level can lie in irregularly spaced locations between old, adjacent grid points and not only midway as is usually the case. For the natural generalization of the four-point scheme introduced by Dubuc and Dyn, Levin, and Gregory, we show that, under some geometric restrictions, the limit function is always C ¹ ; under slightly stronger restrictions we show that the limit function is almost C ² , the same regularity as in the regularly spaced case. May 27, 1997. Date revised: March 10, 1998. Date accepted: March 28, 1998.     

Continuous Extendibility of Solutions of the Neumann Problem for the Laplace Equation

A necessary and sufficient condition for the continuous extendibility of a solution of the Neumann problem for the Laplace equation is given.     

Exponentials Reproducing Subdivision Schemes

This paper is concerned with a family of nonstationary, interpolatory subdivision schemes that have the capability of reproducing functions in a finite-dimensional subspace of exponential polynomials. We give conditions for the existence and uniqueness of such schemes, and analyze their convergence and smoothness. It is shown that the refinement rules of an even-order exponentials reproducing scheme converge to the Dubuc—Deslauriers interpolatory scheme of the same order, and that both schemes have the same smoothness. Unlike the stationary case, the application of a nonstationary scheme requires the computation of a different rule for each refinement level. We show that the rules of an exponentials reproducing scheme can be efficiently derived by means of an auxiliary orthogonal scheme , using only linear operations. The orthogonal schemes are also very useful tools in fitting an appropriate space of exponential polynomials to a given data sequence.     

Commutation for Irregular Subdivision

We present a generalization of the commutation formula to irregular subdivision schemes and wavelets. We show how, in the noninterpolating case, the divided differences need to be adapted to the subdivision scheme. As an example we include the construction of an entire family of biorthogonal compactly supported irregular knot B-spline wavelets starting from Lagrangian interpolation. September 4, 1998. Date revised: July 27, 1999. Date accepted: November 16, 2000.     

Polynomial Reproduction in Subdivision

We study conditions on the matrix mask of a vector subdivision scheme ensuring that certain polynomial input vectors yield polynomial output again. The conditions are in terms of a recurrence formula for the vectors which determine the structure of polynomial input with this property. From this recurrence, we obtain an algorithm to determine polynomial input of maximal degree. The algorithm can be used in the design of masks to achieve a high order of polynomial reproduction.     

Subdivision algorithms converge quadratically

This paper is concerned with determining the exact convergence rates of subdivision algorithms for various settings of polynomial and spline curve or surface representations.     

Vertex-Rounding a Three-Dimensional Polyhedral Subdivision

Let P be a polyhedral subdivision in R ³ with a total of n faces. We show that there is an embedding σ of the vertices, edges, and facets of P into a subdivision Q , where every vertex coordinate of Q is an integral multiple of . For each face f of P , the Hausdorff distance in the L _∈fty metric between f and σ(f) is at most 3/2 . The embedding σ preserves or collapses vertical order on faces of P . The subdivision Q has O(n ⁴ ) vertices in the worst case, and can be computed in the same time. Received September 3, 1997, and in revised form March 29, 1999.     

Subdivision schemes with nonnegative masks

The conjecture concerning the characterization of a convergent univariate subdivision algorithm with nonnegative finite mask is confirmed.

     

INTERPOLATION BY LOOP＇S SUBDIVISION FUNCTIONS

For the problem of constructing smooth functions over arbitrary surfaces from discretedata, we propose to use Loop‘s subdivision functions as the interpolants. Results on theexistence, uniqueness and error bound of the interpolants are established. An efficientprogressive computation algorithm for the interpolants is also presented.     

Subdivision rules and virtual endomorphisms

Suppose f : S ² → S ² is a postcritically finite branched covering without periodic branch points. If f is the subdivision map of a finite subdivision rule with mesh going to zero combinatorially, then the virtual endomorphism on the orbifold fundamental group associated to f is contracting. This is a first step in a program to clarify the relationships among various notions of expansion for noninvertible dynamical systems with branching behavior.      

Subdivision Schemes and Irregular Grids

The present paper deals with subdivision schemes associated with irregular grids. We first give a sufficient condition concerning the difference scheme to obtain convergence. This condition generalizes a necessary and sufficient condition for convergence known in the case of uniform and stationary schemes associated with a regular grid. Through this sufficient condition, convergence of a given subdivision scheme can be proved by comparison with another scheme. Indeed, when two schemes are equivalent in some sense, and when one satisfies the sufficient condition for convergence, the other also satisfies it and it therefore converges too. We also study the smoothness of the limit functions produced by a scheme which satisfies the sufficient condition. Finally, the results are applied to the study of Lagrange interpolating subdivision schemes of any degree, with respect to particular irregular grids.     

Paired-Domination Subdivision Numbers of Graphs

A paired-dominating set of a graph G = (V, E) with no isolated vertex is a dominating set of vertices whose induced subgraph has a perfect matching. The paired-domination number of G, denoted by γ _pr (G), is the minimum cardinality of a paired-dominating set of G. The paired-domination subdivision number sd _γpr (G) is the minimum number of edges that must be subdivided (each edge in G can be subdivided at most once) in order to increase the paired-domination number. In this paper we establish upper bounds on the paired-domination subdivision number and pose some problems and conjectures.     

Smoothness of Nonlinear Median-Interpolation Subdivision

We give a refined analysis of the Hölder regularity for the limit functions arising from a nonlinear pyramid algorithm for robust removal of non-Gaussian noise proposed by Donoho and Yu [6,7,17]. The synthesis part of this algorithm can be interpreted as a nonlinear triadic subdivision scheme where new points are inserted based on local quadratic polynomial median interpolation and imputation. We introduce the analogon of the Donoho–Yu scheme for dyadic refinement, and show that its limit functions are in C for >log₄(128/31)=1.0229.... In the triadic case, we improve the lower bound of >log₂(135/121)=0.0997... previously obtained in [6] to >log₃(135/53)=0.8510.... These lower bounds are relatively close to the anticipated upper bounds of log₂(16/7)=1.1982... in the dyadic, respectivly 1 in the triadic cases, and have been obtained by deriving recursive inequalities for the norm of second rather than first order differences of the sequences arising in the subdivision process.     

Edgewise Subdivision of a Simplex

In this paper we introduce the abacus model of a simplex and use it to subdivide a d -simplex into k ^d d -simplices all of the same volume and shape characteristics. The construction is an extension of the subdivision method of Freudenthal [3] and has been used by Goodman and Peters [4] to design smooth manifolds. Received June 24, 1999, and in revised form January 13, 2000. Online publication August\/ 11, 2000.