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Proof Mining for Nonlinear Operator Theory: Four Case Studies on Accretive Operators, the Cauchy Problem and Nonexpansive Semigroups

Koutsoukou-Argyraki, Angeliki (2017)
Proof Mining for Nonlinear Operator Theory: Four Case Studies on Accretive Operators, the Cauchy Problem and Nonexpansive Semigroups.
Technische Universität Darmstadt
Ph.D. Thesis, Primary publication

Abstract

We present the first applications of proof mining to the theory of partial differential equations as well as to set-valued operators in Banach spaces, in particular to abstract Cauchy problems generated by set-valued nonlinear operators that fulfill certain accretivity conditions. In relation to (various versions of) uniform accretivity we introduce a new notion of modulus of accretivity. A central result is an extraction of effective bounds on the convergence of the solution of the Cauchy problem to the zero of the operator that generates it. We also provide an example of an application for a specific partial differential equation.

For such operators as well as for operators fulfilling the so-called $\phi$-expansivity property, again in general real Banach spaces, we give computable rates of convergence of their resolvents to their zeros.

We give two applications of proof mining to nonlinear nonexpansive semigroups, analysing two completely different proofs of essentially the same statement and obtaining completely different bounds. More specifically we obtain effective bounds for the computation of the approximate common fixed points of one-parameter nonexpansive semigroups on a subset of a Banach space and (for a convex subset) we give corollaries on their asymptotic regularity with respect to Krasnoselskii's and Kuhfittig's iteration schemata.

The bounds obtained in all the above works are all not only effective, but also highly uniform and of low complexity.

We finally include a short comment on a different perspective of a (potential) proof-theoretic application to partial differential equations, namely a reverse mathematical study of a proof for the existence of a weak solution of the Navier-Stokes equations motivating future work.

Item Type: Ph.D. Thesis
Erschienen: 2017
Creators: Koutsoukou-Argyraki, Angeliki
Type of entry: Primary publication
Title: Proof Mining for Nonlinear Operator Theory: Four Case Studies on Accretive Operators, the Cauchy Problem and Nonexpansive Semigroups
Language: English
Referees: Kohlenbach, Prof. Dr. Ulrich ; Garcia Falset, Prof., PhD Jesus ; Yokoyama, PhD Keita
Date: 12 March 2017
Place of Publication: Darmstadt
Refereed: 21 December 2016
URL / URN: http://tuprints.ulb.tu-darmstadt.de/6101
Abstract:

We present the first applications of proof mining to the theory of partial differential equations as well as to set-valued operators in Banach spaces, in particular to abstract Cauchy problems generated by set-valued nonlinear operators that fulfill certain accretivity conditions. In relation to (various versions of) uniform accretivity we introduce a new notion of modulus of accretivity. A central result is an extraction of effective bounds on the convergence of the solution of the Cauchy problem to the zero of the operator that generates it. We also provide an example of an application for a specific partial differential equation.

For such operators as well as for operators fulfilling the so-called $\phi$-expansivity property, again in general real Banach spaces, we give computable rates of convergence of their resolvents to their zeros.

We give two applications of proof mining to nonlinear nonexpansive semigroups, analysing two completely different proofs of essentially the same statement and obtaining completely different bounds. More specifically we obtain effective bounds for the computation of the approximate common fixed points of one-parameter nonexpansive semigroups on a subset of a Banach space and (for a convex subset) we give corollaries on their asymptotic regularity with respect to Krasnoselskii's and Kuhfittig's iteration schemata.

The bounds obtained in all the above works are all not only effective, but also highly uniform and of low complexity.

We finally include a short comment on a different perspective of a (potential) proof-theoretic application to partial differential equations, namely a reverse mathematical study of a proof for the existence of a weak solution of the Navier-Stokes equations motivating future work.

Alternative Abstract:
Alternative abstract Language

In dieser Arbeit werden die ersten Proof-Mining-Anwendungen auf die Theorie Partieller Differentialgleichungen sowie auf mehrwertige Operatoren in Banachräumen präsentiert. Vor allem werden abstrakte Cauchy-Probleme, die durch mehrwertige nichtlineare Operatoren generiert werden, welche bestimmte Akkretivitätsbedingungen erfüllen, betrachtet. Ein neuer Begriff von Akkretivitätsmodul wird eingeführt, der sich auf verschiedene Varianten von uniformer Akkretivität bezieht. Das zentrale Ergebnis dieser Arbeit ist die Extraktion von effektiven Schranken für die Konvergenz der Lösung des Cauchy-Problems gegen die Nullstelle des erzeugenden Operators der es generiert. Ein Anwendungsbeispiel auf eine spezifische partielle Differentialgleichung wird ebenfalls präsentiert.

Für solche Operatoren in allgemeinen reellen Banachräumen sowie für Operatoren, welche die sogenannte $\phi$-Expansivitätseigenschaft haben, werden berechenbare Konvergenzraten ihrer Resolventen gegen ihre entsprechenden Nullstellen angegeben. Unter der Annahme, dass der Raum darüber hinaus gleichmäßig konvex ist, wird eine Konvergenzrate von geringer Komplexität bewiesen.

Zwei Proof-Mining-Anwendungen auf nichtlineare, nichtexpansive Halbgruppen werden durch die Analyse von zwei komplett unterschiedlichen Beweisen derselben Aussage und durch das Erreichen von unterschiedlichen Schranken vorgestellt. Genauer gesagt werden effektive Schranken für die Berechnung von approximativen gemeinsamen Fixpunkten von einparameter-nichtexpansiven Halbgruppen auf einer Teilmenge eines Banachraums gewonnen. Desweiteren präsentieren wir für eine konvexe Teilmenge Korollare über die asymptotische Regularität der Iterationsschemata von Krasnoselskii und Kuhfittig.

Alle erreichten Schranken sind nicht nur effektiv, sondern auch in hohem Maße uniform und haben eine geringe Komplexität.

Diese Dissertation endet mit einem kurzen Kommentar zu einer Idee aus dem Bereich der Reverse Mathematics zu partiellen Differentialgleichungen, die eine andere Perspektive auf potentielle beweistheoretische Anwendungen aufzeigt, um zukünftige Arbeit zu motivieren.

German
URN: urn:nbn:de:tuda-tuprints-61015
Classification DDC: 500 Science and mathematics > 510 Mathematics
Divisions: 04 Department of Mathematics > Analysis
04 Department of Mathematics > Logic
04 Department of Mathematics > Logic > Extraction of Effective Bounds
04 Department of Mathematics
Date Deposited: 19 Mar 2017 20:55
Last Modified: 19 Mar 2017 20:55
PPN:
Referees: Kohlenbach, Prof. Dr. Ulrich ; Garcia Falset, Prof., PhD Jesus ; Yokoyama, PhD Keita
Refereed / Verteidigung / mdl. Prüfung: 21 December 2016
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