Hahn-Banach Theorem, Polynomial Approximation, Moment Problems, and Related Inverse Problems

A special issue of Mathematics (ISSN 2227-7390). This special issue belongs to the section "Engineering Mathematics".

Deadline for manuscript submissions: closed (31 July 2021) | Viewed by 5890

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Department of Mathematics-Informatics, University Politehnica of Bucharest, Splaiul Independentei 313, 060042 Bucharest, Romania
Interests: Hahn-Banach-type theorems; Markov moment problems; polynomial approximation on special unbounded subsets; charaterization of isotonicity of convex operators defined on a convex cone
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Special Issue Information

Dear Colleagues,

As is well-known, Hahn-Banach-type results have their main applications in solving moment problems, the subdifferentiability of convex operators, controlled regularity, and characterizing the isotonicity of convex operators defined on a convex cone in terms of their subdifferentials. Such problems represent motivations of finding necessary and sufficient conditions for the existence of a linear extension from a vector subspace to the entire domain space, which is dominated by a convex operator and dominates a concave operator. These convex (and, respectively, concave) operators are defined on arbitrary convex subsets. For applications, topological versions of such results are emphasized. In this respect, the continuous convex-dominating operator usually controls the norm of the linear extension. Polynomial approximation on Cartesian products of unbounded closed intervals has been also applied to characterize the existence and uniqueness of the solution for some Markov moment problems in terms of quadratic forms. One partially solves the difficulty arising from the fact that, in several dimensions, there exist nonnegative polynomials that are not sums of squares. We invite the authors of related papers to submit them for publication in this Special Issue.

Prof. Dr. Octav Olteanu
Guest Editor

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Keywords

  • Hahn-Banach theorem
  • Markov moment problems
  • Markov operators
  • polynomial approximation
  • quadratic forms
  • isotone convex operators over a convex cone

Published Papers (3 papers)

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Research

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26 pages, 509 KiB  
Article
Quasi-Deterministic Processes with Monotonic Trajectories and Unsupervised Machine Learning
by Andrey V. Orekhov
Mathematics 2021, 9(18), 2301; https://doi.org/10.3390/math9182301 - 17 Sep 2021
Cited by 3 | Viewed by 1809
Abstract
This paper aims to consider approximation-estimation tests for decision-making by machine-learning methods, and integral-estimation tests are defined, which is a generalization for the continuous case. Approximation-estimation tests are measurable sampling functions (statistics) that estimate the approximation error of monotonically increasing number sequences in [...] Read more.
This paper aims to consider approximation-estimation tests for decision-making by machine-learning methods, and integral-estimation tests are defined, which is a generalization for the continuous case. Approximation-estimation tests are measurable sampling functions (statistics) that estimate the approximation error of monotonically increasing number sequences in different classes of functions. These tests make it possible to determine the Markov moments of a qualitative change in the increase in such sequences, from linear to nonlinear type. If these sequences are trajectories of discrete quasi-deterministic random processes, then moments of change in the nature of their growth and qualitative change in the process match up. For example, in cluster analysis, approximation-estimation tests are a formal generalization of the “elbow method” heuristic. In solid mechanics, they can be used to determine the proportionality limit for the stress strain curve (boundaries of application of Hooke’s law). In molecular biology methods, approximation-estimation tests make it possible to determine the beginning of the exponential phase and the transition to the plateau phase for the curves of fluorescence accumulation of the real-time polymerase chain reaction, etc. Full article
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15 pages, 436 KiB  
Article
Stieltjes and Hamburger Reduced Moment Problem When MaxEnt Solution Does Not Exist
by Pier Luigi Novi Inverardi and Aldo Tagliani
Mathematics 2021, 9(4), 309; https://doi.org/10.3390/math9040309 - 4 Feb 2021
Cited by 12 | Viewed by 1486
Abstract
For a given set of moments whose predetermined values represent the available information, we consider the case where the Maximum Entropy (MaxEnt) solutions for Stieltjes and Hamburger reduced moment problems do not exist. Genuinely relying upon MaxEnt rationale we find the distribution with [...] Read more.
For a given set of moments whose predetermined values represent the available information, we consider the case where the Maximum Entropy (MaxEnt) solutions for Stieltjes and Hamburger reduced moment problems do not exist. Genuinely relying upon MaxEnt rationale we find the distribution with largest entropy and we prove that this distribution gives the best approximation of the true but unknown underlying distribution. Despite the nice properties just listed, the suggested approximation suffers from some numerical drawbacks and we will discuss this aspect in detail in the paper. Full article
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Review

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16 pages, 317 KiB  
Review
From Hahn–Banach Type Theorems to the Markov Moment Problem, Sandwich Theorems and Further Applications
by Octav Olteanu
Mathematics 2020, 8(8), 1328; https://doi.org/10.3390/math8081328 - 10 Aug 2020
Cited by 5 | Viewed by 1895
Abstract
The aim of this review paper is to recall known solutions for two Markov moment problems, which can be formulated as Hahn–Banach extension theorems, in order to emphasize their relationship with the following problems: (1) pointing out a previously published sandwich theorem of [...] Read more.
The aim of this review paper is to recall known solutions for two Markov moment problems, which can be formulated as Hahn–Banach extension theorems, in order to emphasize their relationship with the following problems: (1) pointing out a previously published sandwich theorem of the type fhg, where f, −g are convex functionals and h is an affine functional, over a finite-simplicial set X, and proving a topological version for this result; (2) characterizing isotonicity of convex operators over arbitrary convex cones; giving a sharp direct proof for one of the generalizations of Hahn–Banach theorem applied to the isotonicity; (3) extending inequalities assumed to be valid on a small subset, to the entire positive cone of the domain space, via Krein–Milman or Carathéodory’s theorem. Thus, we point out some earlier, as well as new applications of the Hahn–Banach type theorems, emphasizing the topological versions of these applications. Full article
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