Intrinsic interpolation, near-circularity and maximal convergence

IF 0.9 3区 数学 Q2 MATHEMATICS
Hans-Peter Blatt
{"title":"Intrinsic interpolation, near-circularity and maximal convergence","authors":"Hans-Peter Blatt","doi":"10.1016/j.jat.2025.106201","DOIUrl":null,"url":null,"abstract":"<div><div>Let <span><math><mi>E</mi></math></span> be compact and connected with <span><math><mrow><mi>cap</mi><mspace></mspace><mi>E</mi><mo>&gt;</mo><mn>0</mn></mrow></math></span> and connected complement <span><math><mrow><mi>Ω</mi><mo>=</mo><mover><mrow><mi>ℂ</mi></mrow><mo>¯</mo></mover><mo>∖</mo><mi>E</mi></mrow></math></span>, let <span><math><mrow><msub><mrow><mi>g</mi></mrow><mrow><mi>Ω</mi></mrow></msub><mrow><mo>(</mo><mi>z</mi><mo>,</mo><mi>∞</mi><mo>)</mo></mrow></mrow></math></span> be the Green’s function of <span><math><mi>Ω</mi></math></span> with pole at infinity and let <span><math><mrow><msub><mrow><mi>E</mi></mrow><mrow><mi>σ</mi></mrow></msub><mo>≔</mo><mrow><mo>{</mo><mi>z</mi><mo>∈</mo><mi>Ω</mi><mo>:</mo><msub><mrow><mi>g</mi></mrow><mrow><mi>Ω</mi></mrow></msub><mrow><mo>(</mo><mi>z</mi><mo>,</mo><mi>∞</mi><mo>)</mo></mrow><mo>&lt;</mo><mo>log</mo><mi>σ</mi><mo>}</mo></mrow><mo>∪</mo><mi>E</mi><mo>,</mo><mspace></mspace><mn>1</mn><mo>&lt;</mo><mi>σ</mi><mo>&lt;</mo><mi>∞</mi><mo>,</mo></mrow></math></span> be the Green domains with boundaries <span><math><msub><mrow><mi>Γ</mi></mrow><mrow><mi>σ</mi></mrow></msub></math></span>. Let <span><math><mi>f</mi></math></span> be holomorphic on <span><math><mi>E</mi></math></span> and let <span><math><mrow><mi>ρ</mi><mrow><mo>(</mo><mi>f</mi><mo>)</mo></mrow></mrow></math></span> denote the maximal parameter of holomorphy of <span><math><mi>f</mi></math></span> and let <span><math><msub><mrow><mfenced><mrow><msub><mrow><mi>p</mi></mrow><mrow><mi>n</mi></mrow></msub></mrow></mfenced></mrow><mrow><mi>n</mi><mo>∈</mo><mi>N</mi></mrow></msub></math></span> be a sequence of polynomials converging maximally to <span><math><mi>f</mi></math></span> on <span><math><mi>E</mi></math></span>. If <span><math><mi>σ</mi></math></span>, <span><math><mrow><mn>1</mn><mo>&lt;</mo><mi>σ</mi><mo>&lt;</mo><mi>ρ</mi><mrow><mo>(</mo><mi>f</mi><mo>)</mo></mrow><mo>&lt;</mo><mi>∞</mi></mrow></math></span>, is fixed and if <span><math><mrow><msub><mrow><mi>m</mi></mrow><mrow><mi>n</mi></mrow></msub><mrow><mo>(</mo><mi>σ</mi><mo>)</mo></mrow></mrow></math></span> denotes the number of interpolation points of <span><math><msub><mrow><mi>p</mi></mrow><mrow><mi>n</mi></mrow></msub></math></span> to <span><math><mi>f</mi></math></span> in <span><math><msub><mrow><mi>E</mi></mrow><mrow><mi>σ</mi></mrow></msub></math></span> with normalized counting measure <span><math><msub><mrow><mi>μ</mi></mrow><mrow><mi>σ</mi><mo>,</mo><mi>n</mi></mrow></msub></math></span>, then there exists a subset <span><math><mrow><mi>Λ</mi><mo>⊂</mo><mi>N</mi></mrow></math></span> such that <span><math><mrow><msub><mrow><mi>m</mi></mrow><mrow><mi>n</mi></mrow></msub><mrow><mo>(</mo><mi>σ</mi><mo>)</mo></mrow><mo>=</mo><mi>n</mi><mo>+</mo><mi>o</mi><mrow><mo>(</mo><mi>n</mi><mo>)</mo></mrow><mspace></mspace><mtext>as</mtext><mspace></mspace><mi>n</mi><mo>∈</mo><mi>Λ</mi><mo>,</mo><mi>n</mi><mo>→</mo><mi>∞</mi><mo>,</mo></mrow></math></span>\n <span><math><mrow><mover><mrow><msub><mrow><msub><mrow><mi>μ</mi></mrow><mrow><mi>σ</mi><mo>,</mo><mi>n</mi></mrow></msub></mrow><mrow><msub><mrow><mo>|</mo></mrow><mrow><mi>E</mi></mrow></msub></mrow></msub></mrow><mrow><mo>̂</mo></mrow></mover><mo>+</mo><msub><mrow><msub><mrow><mi>μ</mi></mrow><mrow><mi>σ</mi><mo>,</mo><mi>n</mi></mrow></msub></mrow><mrow><msub><mrow><mo>|</mo></mrow><mrow><mi>Ω</mi></mrow></msub></mrow></msub><mspace></mspace><mover><mrow><mo>⟶</mo></mrow><mrow><mo>∗</mo></mrow></mover><mspace></mspace><msub><mrow><mi>μ</mi></mrow><mrow><mi>E</mi></mrow></msub><mspace></mspace><mtext>as</mtext><mspace></mspace><mi>n</mi><mo>∈</mo><mi>Λ</mi><mo>,</mo><mi>n</mi><mo>→</mo><mi>∞</mi><mo>,</mo></mrow></math></span> where <span><math><mrow><msub><mrow><mi>μ</mi></mrow><mrow><mi>σ</mi><mo>,</mo><mi>n</mi></mrow></msub><mo>=</mo><msub><mrow><msub><mrow><mi>μ</mi></mrow><mrow><mi>σ</mi><mo>,</mo><mi>n</mi></mrow></msub></mrow><mrow><msub><mrow><mo>|</mo></mrow><mrow><mi>E</mi></mrow></msub></mrow></msub><mo>+</mo><msub><mrow><msub><mrow><mi>μ</mi></mrow><mrow><mi>σ</mi><mo>,</mo><mi>n</mi></mrow></msub></mrow><mrow><msub><mrow><mo>|</mo></mrow><mrow><mi>Ω</mi></mrow></msub></mrow></msub></mrow></math></span>, <span><math><mover><mrow><msub><mrow><msub><mrow><mi>μ</mi></mrow><mrow><mi>σ</mi><mo>,</mo><mi>n</mi></mrow></msub></mrow><mrow><msub><mrow><mo>|</mo></mrow><mrow><mi>E</mi></mrow></msub></mrow></msub></mrow><mrow><mo>̂</mo></mrow></mover></math></span> denotes the balayage measure of <span><math><msub><mrow><msub><mrow><mi>μ</mi></mrow><mrow><mi>σ</mi><mo>,</mo><mi>n</mi></mrow></msub></mrow><mrow><msub><mrow><mo>|</mo></mrow><mrow><mi>E</mi></mrow></msub></mrow></msub></math></span> onto the boundary of <span><math><mi>E</mi></math></span> and <span><math><msub><mrow><mi>μ</mi></mrow><mrow><mi>E</mi></mrow></msub></math></span> is the equilibrium measure of <span><math><mi>E</mi></math></span>. Moreover, there exists a sequence <span><math><msub><mrow><mfenced><mrow><msub><mrow><mi>σ</mi></mrow><mrow><mi>n</mi></mrow></msub></mrow></mfenced></mrow><mrow><mi>n</mi><mo>∈</mo><mi>Λ</mi></mrow></msub></math></span> converging to <span><math><mi>σ</mi></math></span> such that the closed curves <span><math><mrow><msub><mrow><mi>γ</mi></mrow><mrow><mi>n</mi></mrow></msub><mo>=</mo><mrow><mo>(</mo><mi>f</mi><mo>−</mo><msub><mrow><mi>p</mi></mrow><mrow><mi>n</mi></mrow></msub><mo>)</mo></mrow><mrow><mo>(</mo><msub><mrow><mi>Γ</mi></mrow><mrow><msub><mrow><mi>σ</mi></mrow><mrow><mi>n</mi></mrow></msub></mrow></msub><mo>)</mo></mrow></mrow></math></span> do not pass through the point 0 and the winding numbers <span><math><mrow><msub><mrow><mtext>Ind</mtext></mrow><mrow><msub><mrow><mi>γ</mi></mrow><mrow><mi>n</mi></mrow></msub></mrow></msub><mrow><mo>(</mo><mn>0</mn><mo>)</mo></mrow></mrow></math></span> satisfy <span><math><mrow><msub><mrow><mtext>Ind</mtext></mrow><mrow><msub><mrow><mi>γ</mi></mrow><mrow><mi>n</mi></mrow></msub></mrow></msub><mrow><mo>(</mo><mn>0</mn><mo>)</mo></mrow><mo>=</mo><msub><mrow><mi>m</mi></mrow><mrow><mi>n</mi></mrow></msub><mrow><mo>(</mo><msub><mrow><mi>σ</mi></mrow><mrow><mi>n</mi></mrow></msub><mo>)</mo></mrow><mo>=</mo><mi>n</mi><mo>+</mo><mi>o</mi><mrow><mo>(</mo><mi>n</mi><mo>)</mo></mrow><mspace></mspace><mtext>as</mtext><mspace></mspace><mi>n</mi><mo>∈</mo><mi>Λ</mi><mo>,</mo><mi>n</mi><mo>→</mo><mi>∞</mi><mo>.</mo></mrow></math></span></div></div>","PeriodicalId":54878,"journal":{"name":"Journal of Approximation Theory","volume":"312 ","pages":"Article 106201"},"PeriodicalIF":0.9000,"publicationDate":"2025-05-24","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":"0","resultStr":null,"platform":"Semanticscholar","paperid":null,"PeriodicalName":"Journal of Approximation Theory","FirstCategoryId":"100","ListUrlMain":"https://www.sciencedirect.com/science/article/pii/S0021904525000590","RegionNum":3,"RegionCategory":"数学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":null,"EPubDate":"","PubModel":"","JCR":"Q2","JCRName":"MATHEMATICS","Score":null,"Total":0}
引用次数: 0

Abstract

Let E be compact and connected with capE>0 and connected complement Ω=¯E, let gΩ(z,) be the Green’s function of Ω with pole at infinity and let Eσ{zΩ:gΩ(z,)<logσ}E,1<σ<, be the Green domains with boundaries Γσ. Let f be holomorphic on E and let ρ(f) denote the maximal parameter of holomorphy of f and let pnnN be a sequence of polynomials converging maximally to f on E. If σ, 1<σ<ρ(f)<, is fixed and if mn(σ) denotes the number of interpolation points of pn to f in Eσ with normalized counting measure μσ,n, then there exists a subset ΛN such that mn(σ)=n+o(n)asnΛ,n, μσ,n|Ê+μσ,n|ΩμEasnΛ,n, where μσ,n=μσ,n|E+μσ,n|Ω, μσ,n|Ê denotes the balayage measure of μσ,n|E onto the boundary of E and μE is the equilibrium measure of E. Moreover, there exists a sequence σnnΛ converging to σ such that the closed curves γn=(fpn)(Γσn) do not pass through the point 0 and the winding numbers Indγn(0) satisfy Indγn(0)=mn(σn)=n+o(n)asnΛ,n.
内禀插值,近圆度和最大收敛
设E是紧致的,并且与capE>;0和连通补Ω=¯∈E相连,设gΩ(z,∞)是Ω的极点在无穷远处的Green函数,设Eσ∈Ω:gΩ(z,∞)<logσ}∪E,1<σ<;∞是有边界的Green域Γσ。让f E和上全纯让ρ(f)表示最大的正则参数f对所测试,让∈N是一个多项式序列收敛最大f E .如果σ,1 & lt;σ& lt;ρ(f) & lt;∞,是固定的,如果mn(σ)表示pn的数量的插值点与规范化计数测量μf Eσσ,N,那么存在一个子集Λ⊂N, mn(σ)= N + o (N) asn∈Λ,N→∞,μσ,N | E +μσ,N |Ω⟶∗μEasn∈Λ,N→∞,在μσ,N =μσ,N | E +μσ,N |Ω,μσ,n|Ê表示μσ的平衡测度,n|E在E的边界上,μE是E的平衡测度,并且存在一个收敛于σ的序列σnn∈Λ,使得闭合曲线γn=(f−pn)(Γσn)不经过0点,圈数Indγn(0)满足Indγn(0)=mn(σn)=n+o(n)asn∈Λ,n→∞。
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来源期刊
CiteScore
1.90
自引率
11.10%
发文量
55
审稿时长
6-12 weeks
期刊介绍: The Journal of Approximation Theory is devoted to advances in pure and applied approximation theory and related areas. These areas include, among others: • Classical approximation • Abstract approximation • Constructive approximation • Degree of approximation • Fourier expansions • Interpolation of operators • General orthogonal systems • Interpolation and quadratures • Multivariate approximation • Orthogonal polynomials • Padé approximation • Rational approximation • Spline functions of one and several variables • Approximation by radial basis functions in Euclidean spaces, on spheres, and on more general manifolds • Special functions with strong connections to classical harmonic analysis, orthogonal polynomial, and approximation theory (as opposed to combinatorics, number theory, representation theory, generating functions, formal theory, and so forth) • Approximation theoretic aspects of real or complex function theory, function theory, difference or differential equations, function spaces, or harmonic analysis • Wavelet Theory and its applications in signal and image processing, and in differential equations with special emphasis on connections between wavelet theory and elements of approximation theory (such as approximation orders, Besov and Sobolev spaces, and so forth) • Gabor (Weyl-Heisenberg) expansions and sampling theory.
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