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Characterization of Smoothness of Multivariate Refinable Functions and Convergence of Cascade Algorithms of Nonhomogeneous Refinement Equations
Authors:Song Li
Affiliation:(1) Department of Mathematics, Zhejiang University, Hangzhou, Zhejiang, 310027, P.R. China
Abstract:
This paper concerns multivariate homogeneous refinement equations of the form

$$varphi (x) = sumlimits_{alpha  in mathbb{Z}^S } {a(alpha )varphi (Mx - alpha ) + {text{ }}x{text{ }} in {text{ }}mathbb{R}} ^s ,$$
and multivariate nonhomogeneous refinement equations of the form

$$varphi (x) = sumlimits_{alpha  in mathbb{Z}^S } {a(alpha )varphi (Mx - alpha ) + g(x){text{ }} in {text{ }}mathbb{R}} ^s ,$$
where phiv=(phiv1,...,phivr)T is the unknown, M is an s×s dilation matrix with m=|detthinspM|, g=(g1,...,gr)T is a given compactly supported vector-valued function on Rs, and a is a finitely supported refinement mask such that each a(agr) is an r×r (complex) matrix. In this paper, we characterize the optimal smoothness of a multiple refinable function associated with homogeneous refinement equations in terms of the spectral radius of the corresponding transition operator restricted to a suitable finite-dimensional invariant subspace when M is an isotropic dilation matrix. Nonhomogeneous refinement equations naturally occur in multi-wavelets constructions. Let phiv0 be an initial vector of functions in the Sobolev space (W2k(Rs))r(kisinN). The corresponding cascade algorithm is given by

$$varphi _n (x) = sumlimits_{alpha  in mathbb{Z}^S } {a(alpha )varphi _n (Mx - alpha ) + g(x),{text{ }} in {text{ }}mathbb{R}} ^s ,n = 1,2....$$
Keywords:refinement equation  refinable function  smoothness  cascade algorithm  Sobolev space  Lipschitz space  transition operator  self-affine tile
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