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Discrete taut strings and real interpolation
Linköping University, Department of Mathematics, Mathematics and Applied Mathematics. Linköping University, Faculty of Science & Engineering.
Linköping University, Department of Mathematics, Mathematics and Applied Mathematics. Linköping University, Faculty of Science & Engineering.
2016 (English)In: Journal of Functional Analysis, ISSN 0022-1236, E-ISSN 1096-0783, Vol. 270, no 2, 671-704 p.Article in journal (Refereed) Published
Resource type
Text
Abstract [en]

Classical taut strings and their multidimensional generalizations appear in a broad range of applications. In this paper we suggest a general approach based on the K-functional of real interpolation that provides a unifying framework of existing theories and extend the range of applications of taut strings. More exactly, we introduce the notion of invariant K-minimal sets, explain their connection to taut strings and characterize all bounded, closed and convex sets in R-n that are invariant K-minimal with respect to the couple (l(1), l(infinity)). (C) 2015 Elsevier Inc. All rights reserved.

Place, publisher, year, edition, pages
ACADEMIC PRESS INC ELSEVIER SCIENCE , 2016. Vol. 270, no 2, 671-704 p.
Keyword [en]
Taut strings; Real interpolation; Invariant K-minimal sets
National Category
Mathematics
Identifiers
URN: urn:nbn:se:liu:diva-124087DOI: 10.1016/j.jfa.2015.10.012ISI: 000366144300007OAI: oai:DiVA.org:liu-124087DiVA: diva2:897224
Available from: 2016-01-25 Created: 2016-01-19 Last updated: 2017-11-30
In thesis
1. Taut Strings and Real Interpolation
Open this publication in new window or tab >>Taut Strings and Real Interpolation
2016 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The taut string problem concerns finding the function with the shortest graph length, i.e. the taut string, in a certain set  of continuous piecewise linear functions. It has appeared in a broad range of applications including statistics, image processing and economics. As it turns out, the taut string has besides minimal graph length also minimal energy and minimal total variation among the functions in Ω.

The theory of real interpolation is based on Peetre’s K-functional. In terms of the K-functional, we introduce invariant K-minimal sets and show a close connection between taut strings and invariant K-minimal sets.

This insight leads to new problems of interpolation theory, gives possibility to generalize the notion of taut strings and provides new applications.

The thesis consists of four papers. In paper I, connections between invariant K-minimal sets and various forms of taut strings are investigated. It is shown that the set Ω′ of the derivatives of the functions in  can be interpreted as an invariant K-minimal set for the Banach couple (ℓ1, ℓ) on Rn. In particular, the derivative of the taut string has minimal K-functional in Ω′. A characterization of all bounded, closed and convex sets in Rn that are invariant K-minimal for (ℓ1, ℓ) is established.

Paper II presents examples of invariant K-minimal sets in Rn for (ℓ1, ℓ). A convergent algorithm for computing the element with minimal K-functional in such sets is given. In the infinite-dimensional setting, a sufficient condition for a set to be invariant K-minimal with respect to the Banach couple L1 ([0,1]m) ,L ([0,1]m) is established. With this condition at hand, different examples of invariant K-minimal sets for this couple are constructed.

Paper III considers an application of taut strings to buffered real-time communication systems. The optimal buffer management strategy, with respect to minimization of a class of convex distortion functions, is characterized in terms of a taut string. Further, an algorithm for computing the optimal buffer management strategy is provided.

In paper IV, infinite-dimensional taut strings are investigated in connection with the Wiener process. It is shown that the average energy per unit of time of the taut string in the long run converges, if it is constrained to stay within the distance r > 0 from the trajectory of a Wiener process, to a constant C2/r2 where C ∈ (0,∞). While the exact value of C is unknown, the numerical estimate C ≈ 0.63 is obtained through simulations on a super computer. These simulations are based on a certain algorithm for constructing finite-dimensional taut strings.

Place, publisher, year, edition, pages
Linköping: Linköping University Electronic Press, 2016. 24 p.
Series
Linköping Studies in Science and Technology. Dissertations, ISSN 0345-7524 ; 1801
National Category
Mathematical Analysis
Identifiers
urn:nbn:se:liu:diva-132421 (URN)10.3384/diss.diva-132421 (DOI)9789176856499 (ISBN)
Public defence
2016-12-02, Nobel BL32, B-huset, Campus Valla, Linköping, 13:15 (English)
Opponent
Supervisors
Available from: 2016-11-10 Created: 2016-11-10 Last updated: 2016-11-10Bibliographically approved

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Kruglyak, NatanSetterqvist, Eric

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