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1
Yang, Liming. "Subnormal operators, hyponormal operators, and mean polynomial approximation." Diss., Virginia Tech, 1993. http://hdl.handle.net/10919/40103.
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We prove quasisimilar subdecomposable operators without eigenvalues have equal essential spectra. Therefore, quasisimilar hyponormal operators have equal essential spectra. We obtain some results on the spectral pictures of cyclic hyponormal operators. An algebra homomorphism π from H∞(G) to L(H) is a unital representation for T if π(1) = I and π(x) = T. It is shown that if the boundary of G has zero area measure, then the unital norm continuous representation for a pure hyponormal operator T is unique and is weak star continuous. It follows that every pure hyponormal contraction is in C.0
Let μ represent a positive, compactly supported Borel measure in the plane, C. For each t in [1, ∞ ), the space Pt(μ) consists of the functions in Lt(μ) that belong to the (norm) closure of the (analytic) polynomials. J. Thomson in [T] has shown that the set of bounded point evaluations, bpe μ, for Pt(μ) is a nonempty simply connected region G. We prove that the measure μ restricted to the boundary of G is absolutely continuous with respect to the harmonic measure on G and the space P2(μ)∩C(spt μ) = A(G), where C(spt μ) denotes the continuous functions on spt μ and A(G) denotes those functions continuous on G ¯ that are analytic on G.
We also show that if a function f in P2(μ) is zero a.e. μ in a neighborhood of a point on the boundary, then f has to be the zero function. Using this result, we are able to prove that the essential spectrum of a cyclic, self-dual, subnormal operator is symmetric with respect to the real axis. We obtain a reduction into the structure of a cyclic, irreducible, self-dual, subnormal operator. One may assume, in this inquiry, that the corresponding P2(μ) space has bpe μ = D. Necessary and sufficient conditions for a cyclic, subnormal operator Sμ with bpe μ = D to have a self-dual are obtained under the additional assumption that the measure on the unit circle is log-integrable.Ph. D.
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Santos, Pedro. "Approximation Methods for Convolution Operators on the Real Line." Doctoral thesis, Universitätsbibliothek Chemnitz, 2005. http://nbn-resolving.de/urn:nbn:de:swb:ch1-200500362.
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This work is concerned with the applicability of several approximation methods (finite section method, Galerkin and collocation methods with maximum defect splines for uniform and non uniform meshes) to operators belonging to the closed subalgebra generated by operators of multiplication bz piecewise continuous functions and convolution operators also with piecewise continuous generating function.
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Silva, Nunes Ana Luisa. "Spectral approximation with matrices issued from discretized operators." Phd thesis, Université Jean Monnet - Saint-Etienne, 2012. http://tel.archives-ouvertes.fr/tel-00952977.
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In this thesis, we consider the numerical solution of a large eigenvalue problem in which the integral operator comes from a radiative transfer problem. It is considered the use of hierarchical matrices, an efficient data-sparse representation of matrices, especially useful for large dimensional problems. It consists on low-rank subblocks leading to low memory requirements as well as cheap computational costs. We discuss the use of the hierarchical matrix technique in the numerical solution of a large scale eigenvalue problem arising from a finite rank discretization of an integral operator. The operator is of convolution type, it is defined through the first exponential-integral function and hence it is weakly singular. We access HLIB (Hierarchical matrices LIBrary) that provides, among others, routines for the construction of hierarchical matrix structures and arithmetic algorithms to perform approximative matrix operations. Moreover, it is incorporated the matrix-vector multiply routines from HLIB, as well as LU factorization for preconditioning, into SLEPc (Scalable Library for Eigenvalue Problem Computations) in order to exploit the available algorithms to solve eigenvalue problems. It is also developed analytical expressions for the approximate degenerate kernels and deducted error upper bounds for these approximations. The numerical results obtained with other approaches to solve the problem are used to compare with the ones obtained with this technique, illustrating the efficiency of the techniques developed and implemented in this work
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Qiu, James Zhijan. "Polynomial approximation and Carleson measures on a general domain and equivalence classes of subnormal operators." Diss., This resource online, 1993. http://scholar.lib.vt.edu/theses/available/etd-06062008-171825/.
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Saad, Nasser. "Geometrical approximation methods for the discrete spectra of Schröedinger operators." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1998. http://www.collectionscanada.ca/obj/s4/f2/dsk1/tape11/PQDD_0017/NQ44809.pdf.
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Hansen, A. C. "On the approximation of spectra of linear Hilbert space operators." Thesis, University of Cambridge, 2008. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.603665.
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The main topic of this thesis is how to approximate and compute spectra of linear operators on separable Hilbert spaces. We consider several approaches including the finite section method, an infinite-dimensional version of the QR algorithm, as well as pseudospectral techniques. Several new theorems about convergence of the finite section method (and variants of it) for self-adjoint problems are obtained together with a rigorous analysis of the infinite-dimensional QR algorithm for normal operators. To attack the general spectral problem we look to the pseudospectral theory and introduce the complexity index. A generalization of the pseudospectrum is introduced, namely, the n-pseudospectrum. This set behaves very much like the original pseudospectrum, but has the advantage that it approximates the spectrum well for large n. The complexity index is a tool for indicating how complex or difficult it may be to approximate spectra of operators belonging to a certain class. We establish bounds on the complexity indeed and discuss some open problems regarding this new mathematical entity. As the approximation framework also gives rise to several computational methods, we analyze and discuss implementation techniques for algorithms that can be derived from the theoretical model. In particular, we develop algorithms that can compute spectra of arbitrary bounded operators on separable Hilbert spaces, and the exposition is followed by several numerical examples. The thesis also contains a thorough discussion on how to implement the QR algorithm in infinite dimensions. This is supported by numerical computations. These examples reveal several surprisingly nice features of the infinite-dimensional QR algorithm, and this leaves a number of open problems that we debate.
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Feijoo, Juan Alejandro Vazquez. "Analysis and identification of nonlinear system using parametric models of Volterra operators." Thesis, University of Sheffield, 2002. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.274962.
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Lindner, Marko. "Fredholm Theory and Stable Approximation of Band Operators and Their Generalisations." Doctoral thesis, Universitätsbibliothek Chemnitz, 2009. http://nbn-resolving.de/urn:nbn:de:bsz:ch1-200901182.
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This text is concerned with the Fredholm theory and stable approximation of bounded
linear operators generated by a class of infinite matrices $(a_{ij})$ that are either
banded or have certain decay properties as one goes away from the main diagonal.
The operators are studied on $\ell^p$ spaces of functions $\Z^N\to X$, where
$p\in[1,\infty]$, $N\in\N$ and $X$ is a complex Banach space. The latter means
that our matrix entries $a_{ij}$ are indexed by multiindices $i,j\in\Z^N$ and
that every $a_{ij}$ is itself a bounded linear operator on $X$. Our main focus
lies on the case $p=\infty$, where new results are derived, and it is demonstrated
in both general theory and concrete operator equations from mathematical physics
how advantage can be taken of these new $p=\infty$ results in the general case
$p\in[1,\infty]$.
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Borovyk, Vita. "Box approximation and related techniques in spectral theory." Diss., Columbia, Mo. : University of Missouri-Columbia, 2008. http://hdl.handle.net/10355/5566.
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Thesis (Ph. D.)--University of Missouri-Columbia, 2008.The entire dissertation/thesis text is included in the research.pdf file; the official abstract appears in the short.pdf file (which also appears in the research.pdf); a non-technical general description, or public abstract, appears in the public.pdf file. Title from title screen of research.pdf file (viewed on June 2, 2009) Vita. Includes bibliographical references.
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Salim, Adil. "Random monotone operators and application to stochastic optimization." Thesis, Université Paris-Saclay (ComUE), 2018. http://www.theses.fr/2018SACLT021/document.
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Cette thèse porte essentiellement sur l'étude d'algorithmes d'optimisation. Les problèmes de programmation intervenant en apprentissage automatique ou en traitement du signal sont dans beaucoup de cas composites, c'est-à-dire qu'ils sont contraints ou régularisés par des termes non lisses. Les méthodes proximales sont une classe d'algorithmes très efficaces pour résoudre de tels problèmes. Cependant, dans les applications modernes de sciences des données, les fonctions à minimiser se représentent souvent comme une espérance mathématique, difficile ou impossible à évaluer. C'est le cas dans les problèmes d'apprentissage en ligne, dans les problèmes mettant en jeu un grand nombre de données ou dans les problèmes de calcul distribué. Pour résoudre ceux-ci, nous étudions dans cette thèse des méthodes proximales stochastiques, qui adaptent les algorithmes proximaux aux cas de fonctions écrites comme une espérance. Les méthodes proximales stochastiques sont d'abord étudiées à pas constant, en utilisant des techniques d'approximation stochastique. Plus précisément, la méthode de l'Equation Differentielle Ordinaire est adaptée au cas d'inclusions differentielles. Afin d'établir le comportement asymptotique des algorithmes, la stabilité des suites d'itérés (vues comme des chaines de Markov) est étudiée. Ensuite, des généralisations de l'algorithme du gradient proximal stochastique à pas décroissant sont mises au point pour resoudre des problèmes composites. Toutes les grandeurs qui permettent de décrire les problèmes à résoudre s'écrivent comme une espérance. Cela inclut un algorithme primal dual pour des problèmes régularisés et linéairement contraints ainsi qu'un algorithme d'optimisation sur les grands graphesThis thesis mainly studies optimization algorithms. Programming problems arising in signal processing and machine learning are composite in many cases, i.e they exhibit constraints and non smooth regularization terms. Proximal methods are known to be efficient to solve such problems. However, in modern applications of data sciences, functions to be minimized are often represented as statistical expectations, whose evaluation is intractable. This cover the case of online learning, big data problems and distributed computation problems. To solve this problems, we study in this thesis proximal stochastic methods, that generalize proximal algorithms to the case of cost functions written as expectations. Stochastic proximal methods are first studied with a constant step size, using stochastic approximation techniques. More precisely, the Ordinary Differential Equation method is adapted to the case of differential inclusions. In order to study the asymptotic behavior of the algorithms, the stability of the sequences of iterates (seen as Markov chains) is studied. Then, generalizations of the stochastic proximal gradient algorithm with decreasing step sizes are designed to solve composite problems. Every quantities used to define the optimization problem are written as expectations. This include a primal dual algorithm to solve regularized and linearly constrained problems and an optimization over large graphs algorithm
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Chakmak, Ryan. "Eigenvalues and Approximation Numbers." Scholarship @ Claremont, 2019. https://scholarship.claremont.edu/cmc_theses/2167.
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While the spectral theory of compact operators is known to many, knowledge regarding the relationship between eigenvalues and approximation numbers might be less known. By examining these numbers in tandem, one may develop a link between eigenvalues and l^p spaces. In this paper, we develop the background of this connection with in-depth examples.
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Potrykus, Alexander. "Roth's method and the Yosida approximation for pseudodifferential operators with negative definite symbols." Thesis, Swansea University, 2005. https://cronfa.swan.ac.uk/Record/cronfa42468.
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This thesis consists of two parts. The first one extends an idea developed by J.P. Roth. He succeeded to construct a Feller semigroup associated with a second order elliptic differential operator L(x D) by investigating the semigroups obtained by freezing the coefficients of L(xD). In Chapter 2 we show that a modification of his method works also for certain pseudodifferential operators with bounded negative definite symbols. Partly we can rely on ideas of E. Popescu. In Chapter 3 we show that if a certain pseudodifferential operator -q(xD) generates a Feller semigroup (Tt)t≥0 then the Feller semigroups (Tt([v]))t≥0 generated by the pseudodifferential operators whose symbols are the Yosida approximations of -q(x,xi)i.e. [formula] converge strongly to (Tt(v))t≥0.
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Azimi, Roushan Tahere. "Inequalities related to norm and numerical radius of operators." Thesis, Pau, 2020. http://www.theses.fr/2020PAUU3002.
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Dans cette thèse, après la présentation des notions et des introductions nécessaires, nous étudionslinégalité Hermite-Hadamard pour les fonctions convexes géométriques. Après, nousdéveloppons les résultats en introduisant la fonction convexe géométrique opérationnelle etnous confirmons linégalité Hermite-Hadamard pour ces sortes de fonctions. Ensuite, nousmontrons certaines améliorations du cas normatif de certaines inégalités opérationnelles célèbres,en montrant le rôle convexe logarithmique de quelques fonctions classées selon lanorme stable et aussi en considérant le lien entre les fonctions convexes géométriques et lesfonctions logarithmiques. De plus, nous confirmons les résultats numériques obtenus pourapprocher une catégorie des fonctions convexes pour leur version opérationnelle et nousaméliorons linégalitéHermite-Hadamard pour certaines fonctions convexes opérationnellesen tant quune utilisation des résultats obtenus. Enfin, nous discutons à propos du rayon numériquedun opérateur qui est équivalent de sa norme opérationnelle et nous présentonsdes résultats concernés. Nous terminons cette thèse en obtenant les bornes supérieures dunombre Berezin dun opérateurIn this thesis, after expressing concepts and necessary preconditions, we investigate Hermite-Hadamard inequality for geometrically convex functions. Then, by introducing operator geometricallyconvex functions, we extend the results and prove Hermite-Hadamard type inequalityfor these kind of functions. In the following, by proving the log-convexity of somefunctions which are based on the unitarily invariant norm and considering the relation betweengeometrically convex functions and log-convex functions, we present several refinementsfor some well-known operator norm inequalities. Also, we prove operator version ofsome numerical results, which were obtained for approximating a class of convex functions,as an application,we refine Hermite-Hadamard inequality for a class of operator convex functions.Finally, we discuss about the numerical radius of an operator which is equivalent withthe operator norm and we state some related results, and by obtaining some upper boundsfor the Berezin number of an operator which is contained in the numerical range of that operator, we finish the thesis
در این رساله، پس از بیان مفاهیم و مقدمات لازم به بررسی نامساوی هرمیت-هادامار برای توابع محدب هندسی پرداخته سپس با معرفی تابع محدب هندسی عملگری، نتایج را توسیع داده و نامساوی هرمیت-هادامار گونه را برای این دست توابع اثبات می کنیم. در ادامه با نشان دادن محدب لگاریتمی بودن چند تابع که براساس نرم پایای یکانی تعریف شده اند، و با در نظر گرفتن ارتباط بین توابع محدب هندسی و توابع محدب لگاریتمی بهبودهایی از حالت نرمی چند نامساوی عملگری معروف ارائه می دهیم. هم چنین نتایج عددی بدست آمده جهت تقریب رده ای از توابع محدب را برای نسخه عملگری آن ها اثبات نموده و به عنوان کاربردی از نتایج حاصل، نامساوی هرمیت-هادامار را برای برخی توابع محدب عملگری بهبود می بخشیم. در نهایت، در مورد شعاع عددی یک عملگر، که معادل با نرم عملگری آن می باشد بحث نموده و به بیان برخی از نتایج مرتبط پرداخته، و با بدست آوردن کران های بالایی از عدد برزین یک عملگر که زیر مجموعه ای از برد عددی آن عملگر می باشد، رساله را به پایان می بریم
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Dillhage, Ruth [Verfasser]. "Computable functional analysis : compact operators on computable banach spaces and computable best approximation / Ruth Dillhage." Hagen : Fernuniversität Hagen, 2012. http://d-nb.info/1025601831/34.
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Beckus, Siegfried [Verfasser], Daniel [Gutachter] Lenz, Jean [Gutachter] Bellissard, and Johannes [Gutachter] Kellendonk. "Spectral approximation of aperiodic Schrödinger operators / Siegfried Beckus ; Gutachter: Daniel Lenz, Jean Bellissard, Johannes Kellendonk." Jena : Friedrich-Schiller-Universität Jena, 2017. http://d-nb.info/1177603594/34.
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Nilsson, Jesper. "An exploration of classical SBP-SAT operators and their minimal size." Thesis, Linnéuniversitetet, Institutionen för matematik (MA), 2021. http://urn.kb.se/resolve?urn=urn:nbn:se:lnu:diva-104379.
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We consider diagonal-norm classical summation-by-parts (SBP) operators us-ing the simultaneous approximation term (SAT) method of imposing boundaryconditions. We derive a formula for the inverse of these SBP-SAT discretizationmatrices. This formula is then used to show that it is possible to construct a secondorder accurate SBP-SAT operator using only seven grid points.
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Lei, Lei. "Markov Approximations: The Characterization of Undermodeling Errors." Diss., CLICK HERE for online access, 2006. http://contentdm.lib.byu.edu/ETD/image/etd1371.pdf.
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Silva, Ricardo Correa da. "Operadores p-compactos e a propriedade de p-aproximação." Universidade de São Paulo, 2013. http://www.teses.usp.br/teses/disponiveis/45/45131/tde-12112013-232741/.
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O objetivo desse trabalho é o estudo dos operadores p-compactos e da propriedade de p-aproximação. Estes conceitos estão relacionados a importantes resultados de A. Gröthendieck sobre compacidade e a propriedade de aproximação que foram generalizados em [21] e estudados em [3], [6] e [7].The purpose of this work is the study of p-compact operators and the p-approximation property. These concepts are connected with important results by A. Gröthendieck about compactness and approximation property that were generalized in [21] and studied in [3], [6] and [7].
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Ardag, Dorukhan. "Examining Optimal Form of Two Scale Approximation (TSA) for Calculating Snl Source Term." UNF Digital Commons, 2014. http://digitalcommons.unf.edu/etd/483.
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Nonlinear four-wave interactions (Snl) are critical for acquiring realistic spectra needed by operational wave models. High computational demand to calculate these interactions led to an approximation method named the Discrete Interaction Approximation (DIA) to be used broadly in the major operational wave models for a long time. However, the accuracy of the DIA has been controversial since it was first introduced and more precise approximations such as the Two Scale Approximation (TSA in short) are now available. The only issue with the initial TSA`s efficiency is performing an order of a magnitude slower than the DIA in speed. This study questions the exactness of the DIA while trying to increase the competence of the TSA by making improvements on its execution time. Particularly, in this thesis, the main effort is on the local scale term of the TSA since it is the part that consumes the most time while running the code. The findings of this work imply that the TSA can improve its operation speed significantly while maintaining its accuracy with making alterations in the code. By decreasing the number of bands in the local scale it is possible to run the TSA up to 7.5 faster than its initial version.
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Bethke, Matthias. "Approximation von Fixpunkten streng pseudokontraktiver Operatoren." Pädagogogische Hochschule “Liselotte Herrmann” Güstrow, 1989. https://slub.qucosa.de/id/qucosa%3A73375.
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In vorliegendem Artikel wird eine Verallgemeinerung eines Approximationsteorems von Chidume /6/ für streng pseudokontraktive Operatoren in Lp beziehungsweise lp-Räumen (mit P =2) angegeben. Es wird ein Verfahren betrachtet, welches von MANN /14/ für reelle Funktionen eingeführt würde.This article gives a generalization of an approximation theorem by Chidume / 6 / for strictly pseudocontractive operators in Lp or lp spaces (with P = 2). We consider a method, which MANN / 14 / had introduced for real functions.
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Langenau, Holger. "Best constants in Markov-type inequalities with mixed weights." Doctoral thesis, Universitätsbibliothek Chemnitz, 2016. http://nbn-resolving.de/urn:nbn:de:bsz:ch1-qucosa-200815.
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Markov-type inequalities provide upper bounds on the norm of the (higher order) derivative of an algebraic polynomial in terms of the norm of the polynomial itself. The present thesis considers the cases in which the norms are of the Laguerre, Gegenbauer, or Hermite type, with respective weights chosen differently on both sides of the inequality. An answer is given to the question on the best constant so that such an inequality is valid for every polynomial of degree at most n. The demanded best constant turns out to be the operator norm of the differential operator. The latter conicides with the tractable spectral norm of its matrix representation in an appropriate set of orthonormal bases. The methods to determine these norms vary tremendously, depending on the difference of the parameters accompanying the weights. Up to a very small gap in the parameter range, asymptotics for the best constant in each of the aforementioned cases are givenMarkovungleichungen liefern obere Schranken an die Norm einer (höheren) Ableitung eines algebraischen Polynoms in Bezug auf die Norm des Polynoms selbst. Diese vorliegende Arbeit betrachtet den Fall, dass die Normen vom Laguerre-, Gegenbauer- oder Hermitetyp sind, wobei die entsprechenden Gewichte auf beiden Seiten unterschiedlich gewählt werden. Es wird die kleinste Konstante bestimmt, sodass diese Ungleichung für jedes Polynom vom Grad höchstens n erfüllt ist. Die gesuchte kleinste Konstante kann als die Operatornorm des Differentialoperators dargestellt werden. Diese fällt aber mit der Spektralnorm der Matrixdarstellung in einem Paar geeignet gewählter Orthonormalbasen zusammen und kann daher gut behandelt werden. Zur Abschätzung dieser Normen kommen verschiedene Methoden zum Einsatz, die durch die Differenz der in den Gewichten auftretenden Parameter bestimmt werden. Bis auch eine kleine Lücke im Parameterbereich wird das asymptotische Verhalten der kleinsten Konstanten in jedem der betrachteten Fälle ermittelt
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Strass, Hannes. "Approximating Operators and Semantics for Abstract Dialectical Frameworks." Universitätsbibliothek Leipzig, 2013. http://nbn-resolving.de/urn:nbn:de:bsz:15-qucosa-102943.
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We provide a systematic in-depth study of the semantics of abstract dialectical frameworks (ADFs), a recent generalisation of Dung\'s abstract argumentation frameworks. This is done by associating with an ADF its characteristic one-step consequence operator and defining various semantics for ADFs as different fixpoints of this operator. We first show that several existing semantical notions are faithfully captured by our definition, then proceed to define new ADF semantics and show that they are proper generalisations of existing argumentation semantics from the literature. Most remarkably, this operator-based approach allows us to compare ADFs to related nonmonotonic formalisms like Dung argumentation frameworks and propositional logic programs. We use polynomial, faithful and modular translations to relate the formalisms, and our results show that both abstract argumentation frameworks and abstract dialectical frameworks are at most as expressive as propositional normal logic programs.
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Joldes, Mioara Maria. "Approximations polynomiales rigoureuses et applications." Phd thesis, Ecole normale supérieure de lyon - ENS LYON, 2011. http://tel.archives-ouvertes.fr/tel-00657843.
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Quand on veut évaluer ou manipuler une fonction mathématique f, il est fréquent de la remplacer par une approximation polynomiale p. On le fait, par exemple, pour implanter des fonctions élémentaires en machine, pour la quadrature ou la résolution d'équations différentielles ordinaires (ODE). De nombreuses méthodes numériques existent pour l'ensemble de ces questions et nous nous proposons de les aborder dans le cadre du calcul rigoureux, au sein duquel on exige des garanties sur la précision des résultats, tant pour l'erreur de méthode que l'erreur d'arrondi.Une approximation polynomiale rigoureuse (RPA) pour une fonction f définie sur un intervalle [a,b], est un couple (P, Delta) formé par un polynôme P et un intervalle Delta, tel que f(x)-P(x) appartienne à Delta pour tout x dans [a,b].Dans ce travail, nous analysons et introduisons plusieurs procédés de calcul de RPAs dans le cas de fonctions univariées. Nous analysons et raffinons une approche existante à base de développements de Taylor.Puis nous les remplaçons par des approximants plus fins, tels que les polynômes minimax, les séries tronquées de Chebyshev ou les interpolants de Chebyshev.Nous présentons aussi plusieurs applications: une relative à l'implantation de fonctions standard dans une bibliothèque mathématique (libm), une portant sur le calcul de développements tronqués en séries de Chebyshev de solutions d'ODE linéaires à coefficients polynômiaux et, enfin, un processus automatique d'évaluation de fonction à précision garantie sur une puce reconfigurable.
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Seidel, Markus. "On some Banach Algebra Tools in Operator Theory." Doctoral thesis, Universitätsbibliothek Chemnitz, 2012. http://nbn-resolving.de/urn:nbn:de:bsz:ch1-qucosa-83750.
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Die vorliegende Arbeit ist der Untersuchung von Operatorfolgen gewidmet, die typischerweise bei der Anwendung von Approximationsverfahren auf stetige lineare Operatoren entstehen. Dabei stehen die Stabilität der Folgen sowie das asymptotische Verhalten gewisser Charakteristika wie Normen, Konditionszahlen, Fredholmeigenschaften und Pseudospektren im Mittelpunkt.
Das Hauptaugenmerk liegt auf der Entwicklung der Theorie für Operatoren auf Banachräumen. Hierbei bildet ein dafür geeigneter Konvergenzbegriff, die sogenannte P-starke Konvergenz, den Ausgangspunkt, welcher das Studium der gewünschten Eigenschaften in einer erstaunlichen Allgemeinheit gestattet.
Die erzielten Resultate kommen, neben einer Reihe weiterer Anwendungen, insbesondere für das Projektionsverfahren für banddominierte Operatoren zum Einsatz.
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Correa, José Rafael 1975. "Approximation algorithms for packing and scheduling problems." Thesis, Massachusetts Institute of Technology, 2004. http://hdl.handle.net/1721.1/17720.
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Thesis (Ph. D.)--Massachusetts Institute of Technology, Sloan School of Management, Operations Research Center, 2004.Includes bibliographical references (p. 149-161).
In this thesis we consider three combinatorial optimization problems. Specifically, we study packing and scheduling questions of relevance in several areas of operations research, including interconnection networks and switch scheduling, VLSI design, and processor scheduling. The first chapter studies a natural edge-coloring question arising from the problem of scheduling packets through an interconnection network. The theoretical model we consider can be seen as a weighted extension of Konig's theorem that states that the minimum number of colors needed to color all edges of a bipartite graph equals the maximum vertex degree. For the weighted generalization, a longstanding open question is to determine the minimum number of colors as a function of n, the maximum total weight adjacent to any vertex. Our main contribution is to show that 2.557n + o(n) colors are sufficient, improving upon earlier work. In the second chapter, we consider the following variant of the classical bin-packing problem: Place a given list of rectangles into the minimum number of unit square bins. In the restricted case where all rectangles are squares, we design an algorithm with an asymptotic performance guarantee arbitrarily close to optimal. In the general case, we give an algorithm that outputs a near-optimal solution, provided it is allowed to use slightly larger bins. Moreover, we extend these algorithmic ideas to handle a number of multidimensional packing problems, obtaining best-known results for several of these.
(cont.) Finally, in the third chapter, we discuss a standard sequencing problem, namely, scheduling precedence-constrained jobs on a single machine to minimize the sum of weighted completion times. We look at the problem from a polyhedral perspective, obtaining, as one of our main results, a generalization of a classical result by Sidney. This new insight allows us to reason that all known 2-approximation algorithms behave similarly. Furthermore, we present a new integer programming model that suggests a strong connection between the scheduling problem and the vertex cover problem.
by José Rafael Correa.
Ph.D.
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Collyer, Benjamin S. "On the Fokker-Planck approximation to the Boltzmann collision operator." Thesis, University of Warwick, 2015. http://wrap.warwick.ac.uk/77691/.
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The Boltzmann equation (BE) is a mesoscopic model that provides a description of how gases undergoing a binary collision process evolve in time, however there is no general analytical approach for finding its solutions and direct numerical treatment using quadrature methods is prohibitively expensive due to the dimensions of the problem. For this reason, models that are able to capture the behaviour of solutions to the BE, but which are simpler to treat numerically and analytically are highly desirable. The Fokker-Planck collision operator is one such collision model, which is suited well to numerical solutions using stochastic particle methods, and is the subject of this thesis. The stochastic numerical solutions of the Fokker-Planck model suffer heavily from noise when the speed of the flow is low. We develop two methods that are able to reduced the variance of the estimators of the particle method. The first is a common random number method, which produces a correlated equilibrium solution where thermodynamic fields are known. The second is a importance sampling method, where weights are attached to the particles. This means that particles close to equilibrium do not contribute to the noise of the estimators. We also develop a randomised quasi-Monte Carlo scheme for solving the diffusion equation, which has a faster rate of convergence than simple Monte Carlo methods. The relative simplicity of the functional form of the Fokker-Planck collision operator makes it possible to find analytic solutions in simple cases. We consider a spatially homogeneous, isotropic gas with elastic collisions in the presence of forcing and dissipation and derive self-consistent non-equilibrium steady-state solutions. Previous numerical evidence exists that suggest such forcing and dissipation mechanisms, widely separated, give rise to steady-states of the BE that are close to Maxwellian, with a direct energy cascade and an inverse particle cascade. Using our analytic solutions, we are able to investigate the dependence of such solutions on the forcing and dissipation scales, and find that in the inertial range, the interaction is non-local. We then show that the “extreme driving” mechanism, responsible for a family of non-universal power-law solutions for inelastic granular gases, where the flux of energy is towards lower scales, is also able to produce inverse energy cascades for the elastic system.
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Lu, Lu. "Approximation procedures for some multi-item inventory systems /." The Ohio State University, 1991. http://rave.ohiolink.edu/etdc/view?acc_num=osu1487694702784846.
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Oakley, Steven James. "Orthogonal polynomials in the approximation of probability distributions." Diss., The University of Arizona, 1990. http://hdl.handle.net/10150/185117.
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An approach to the problem of approximating a continuous probability distribution with a series in orthogonal polynomials is presented. The approach is first motivated with a discussion of theoretical distributions which are inherently difficult to evaluate. Additionally, a practical application which involves such a distribution is developed. The three families of orthogonal polynomials that pertain to the methodology--the Hermite, Laguerre, and Jacobi--are then introduced. Important properties and characterizations of these polynomials are given to lay the mathematical framework for the orthogonal polynomial series representation of the probability density function of a continuous random variable. This representation leads to a similar series for the cumulative distribution function, which is of more practical use for computing probabilities associated with the random variable. It is demonstrated that the representations require only the moments and the domain of the random variable to be known. Relationships of the Hermite, Laguerre, and Jacobi series approximations to the normal, gamma, and beta probability distributions, respectively, are also formally established. Examples and applications of the series are given with appropriate analyses to validate the accuracy of the approximation.
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Oram, John A. "Best approximations from certain classes of functions defined by integral operators." Thesis, University of Newcastle Upon Tyne, 1992. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.386590.
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Langenau, Holger. "Best constants in Markov-type inequalities with mixed weights." Doctoral thesis, Universitätsverlag der Technischen Universität Chemnitz, 2015. https://monarch.qucosa.de/id/qucosa%3A20429.
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Markov-type inequalities provide upper bounds on the norm of the (higher order) derivative of an algebraic polynomial in terms of the norm of the polynomial itself. The present thesis considers the cases in which the norms are of the Laguerre, Gegenbauer, or Hermite type, with respective weights chosen differently on both sides of the inequality. An answer is given to the question on the best constant so that such an inequality is valid for every polynomial of degree at most n.
The demanded best constant turns out to be the operator norm of the differential operator. The latter conicides with the tractable spectral norm of its matrix representation in an appropriate set of orthonormal bases.
The methods to determine these norms vary tremendously, depending on the difference of the parameters accompanying the weights. Up to a very small gap in the parameter range, asymptotics for the best constant in each of the aforementioned cases are given.Markovungleichungen liefern obere Schranken an die Norm einer (höheren) Ableitung eines algebraischen Polynoms in Bezug auf die Norm des Polynoms selbst. Diese vorliegende Arbeit betrachtet den Fall, dass die Normen vom Laguerre-, Gegenbauer- oder Hermitetyp sind, wobei die entsprechenden Gewichte auf beiden Seiten unterschiedlich gewählt werden. Es wird die kleinste Konstante bestimmt, sodass diese Ungleichung für jedes Polynom vom Grad höchstens n erfüllt ist. Die gesuchte kleinste Konstante kann als die Operatornorm des Differentialoperators dargestellt werden. Diese fällt aber mit der Spektralnorm der Matrixdarstellung in einem Paar geeignet gewählter Orthonormalbasen zusammen und kann daher gut behandelt werden. Zur Abschätzung dieser Normen kommen verschiedene Methoden zum Einsatz, die durch die Differenz der in den Gewichten auftretenden Parameter bestimmt werden. Bis auch eine kleine Lücke im Parameterbereich wird das asymptotische Verhalten der kleinsten Konstanten in jedem der betrachteten Fälle ermittelt.
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Rhee, Donguk. "Faster fully polynomial approximation schemes for Knapsack problems." Thesis, Massachusetts Institute of Technology, 2015. http://hdl.handle.net/1721.1/98564.
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Thesis: S.M., Massachusetts Institute of Technology, Sloan School of Management, Operations Research Center, 2015.This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections.
Cataloged from student-submitted PDF version of thesis.
Includes bibliographical references (pages 61-62).
A fully polynomial time approximation scheme (FPTAS) is an algorithm that returns ... -optimal solution to a maximization problem of size n, which runs in polynomial time in both ... We develop faster FPTASs for several classes of knapsack problems. In this thesis, we will first survey the relevant literature in FPTASs for knapsack problems. We propose the use of floating point arithmetic rather than the use of geometric rounding in order to simplify analysis. Given a knapsack problem that yield an ... -optimal solution for disjoint subsets S and T of decision variables, we show how to attain ... -optimal solution for the knapsack problem for the set ... We use this procedure to speed up the run-time of FPTASs for: 1. The Integer Knapsack Problem, 2. The Unbounded Integer Knapsack Problem, 3. The Multiple-Choice Knapsack Problem, and, 4. The Nonlinear Integer Knapsack Problem, Using addition ideas, we develop a fast fully polynomial time randomized approximation scheme (FPTAS) for the 0-1 Knapsack Problem, which has the run-time of ...
by Donguk Rhee.
S.M.
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Mostagir, Mohamed. "Fully polynomial time approximation schemes for sequential decision problems." Thesis, Massachusetts Institute of Technology, 2005. http://hdl.handle.net/1721.1/33673.
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Thesis (S.M.)--Massachusetts Institute of Technology, Sloan School of Management, Operations Research Center, 2005.Includes bibliographical references (p. 65-67).
This thesis is divided into two parts sharing the common theme of fully polynomial time approximation schemes. In the first part, we introduce a generic approach for devising fully polynomial time approximation schemes for a large class of problems that we call list scheduling problems. Our approach is simple and unifying, and many previous results in the literature follow as direct corollaries of our main theorem. In the second part, we tackle a more difficult problem; the stochastic lot sizing problem, and give the first fully polynomial time approximation scheme for it. Our approach is based on simple techniques that could arguably have wider applications outside of just designing fully polynomial time approximation schemes.
by Mohamed Mostagir.
S.M.
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Marchina, Bastien. "Tests d'adéquation basés sur la fonction caractéristique." Thesis, Montpellier 2, 2011. http://www.theses.fr/2011MON20088/document.
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Cette thèse est consacré aux tests d'adéquation basés sur la fonction caractéristique. Nous débutons en présentant et en complétant les résultats probabilistes nécessaires à la construction de statistiques de test prenant la fonction caractéristique et son pendant la fonction caractéristique empirique comme représentations respectives des lois de référence et de la loi inconnue de l'échantillon de vecteurs aléatoires à tester. Nous poursuivons le travail en faisant la revue et en classant les tests basés sur la fonction caractéristique existants. Nous élaborons ensuite une classe de statistiques de test s'appuyant sur le calcul d'une distance intégrale. Le cas de la distance L2 est étudié plus à fond, car nous avons pu établir des résultats asymptotiques dans ce dernier cas. Ceux-ci font intervenir les éléments propres inconnus d'un opérateur intégral. Nous présentons, puis utilisons, une méthode d'approximation spectrale basée sur une projection de l'opérateur sur une base orthonormée.Finalement, nous construisons une nouvelle classe de tests appartenant au paradigme des tests lisses de Neyman. L'étude précédente nous permet de simplifier considérablement la construction de ces tests, dont différentes versions sont proposées tant pour le test d'une hypothèse simple que pour le test d'une hypothèse compositeThis PhD thesis consists in building goodness-of-fit tests using the characteristic function (CF) as a prefered representation for the probability laws involved.We start with listing and improving results in probability theory necessary to build test statistics using the characteristic function and its conterpart the empirical characteristic function.We list and classify existing characteristic function based goodness-of-fit tests published by varions authors since 1977.Then, we build a class of tests based on integral metrics. We take particular attention to the case where the statistics are build using a L2 distance. More specifically, we give asymptotic results in this case. However, these results reveal the need for information on the unknown eigenelements of an integral operator. Thus, we present and implement an approximation method using a sequence of projections on orthonormal bases ofan hilbertian functional space.Finally, we will build another class of tests using the Neyman smooth test paradigm. This study is based on our previous results, that fit well into the construction of characteristic function based smooth tests. We give various applications, presenting tests for both a simple hypothesis and a composite hypothesis
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Pozzi, Élodie. "Propriétés spectrales et universalité d’opérateurs de composition pondérés." Thesis, Lyon 1, 2011. http://www.theses.fr/2011LYO10186.
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Cette thèse est dédiée à l'étude d'opérateurs de composition pondérés sur plusieurs espaces fonctionnels sous fond du problème du sous-espace invariant. Cet important problème ouvert pose la question de l'existence pour tout opérateur sur un espace de Hilbert, complexe, séparable de dimension infinie, d'un sous-espace fermé, non-trivial et invariant par cet opérateur. La première partie est consacrée à l'étude spectrale et à la caractérisation des vecteurs cycliques d'un opérateur de composition à poids particulier sur L^2([0,1]^d) : l'opérateur de type Bishop, introduit comme possible contre-exemple au problème du sous-espace invariant. Les seconde, troisième et quatrième parties abordent ce problème sous un autre aspect : celui de l'universalité d'un opérateur. Ces opérateurs universels possèdent la propriété d'universalité : la description complète des sous-espaces invariants d'un opérateur universel permettrait de répondre au problème du sous-espace invariant. Déterminer l'universalité d'un opérateur repose sur l'établissement de propriétés spectrales fines de l’opérateur considéré (théorème de Caradus). Dans ce but, nous établissons des propriétés spectrales ad-hoc de classes d’opérateurs de composition à poids sur L^2([0,1]), les espaces de Sobolev d’ordre n, sur les espaces de Hardy du disque unité et du demi-plan supérieur, permettant de déduire des résultats d’universalité. Nous obtenons aussi une généralisation du critère d’universalité. Dans la dernière partie, nous donnons une caractérisation des opérateurs de composition rsid16415432 inversibles et une caractérisation partielle des opérateurs de composition isométriques sur les espaces de Hardy de l’anneauIn this thesis, we study classes of weighted composition operators on several functional spaces in the background of the invariant subspace problem. This important open problem asks the question of the existence for every operator, defined on a complex and separable infinite dimensional Hilbert space, of a non trivial closed subspace invariant under the operator. The first part is dedicated to the establishment of the spectrum and the characterization of cyclic vectors of a special weighted composition operator defined on L^2([0,1]^d) : the Bishop type operator, introduced as possible counter-example of the invariant subspace problem. The second, third and fourth part approach the problem from the point of view of universal operators. More precisely, universal operators have the universal property in the sense of the complete description of all the invariant subspaces of a universal operator could solve the invariant subspace problem. A sufficient condition for an operator to be universal (Caradus’theorem) is given in terms of spectral properties. To this aim, we establish ad-hoc spectral properties of a class of weighted composition operators on L^2([0,1]) and Sobolev spaces of order n, of composition operator in the Hardy space of the unit disc and of the upper half-plane, which lead us to deduce universality results. We also obtain a generalization of the universality criteria mentioned above. In the last part, we give a characterization of invertible composition operators and a partial characterization of composition operators on the Hardy space of the annulus
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Hed, Lisa. "Approximation and Subextension of Negative Plurisubharmonic Functions." Licentiate thesis, Umeå : Department of Mathematics and Mathematical Statistics, Umeå University, 2008. http://urn.kb.se/resolve?urn=urn:nbn:se:umu:diva-1799.
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Meyers, Carol Ph D. Massachusetts Institute of Technology. "Network flow problems and congestion games : complexity and approximation results." Thesis, Massachusetts Institute of Technology, 2006. http://hdl.handle.net/1721.1/35919.
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This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections.Thesis (Ph. D.)--Massachusetts Institute of Technology, Sloan School of Management, Operations Research Center, 2006.
Includes bibliographical references (p. 155-164).
(cont.) We first address the complexity of finding an optimal minimum cost solution to a congestion game. We consider both network and general congestion games, and we examine several variants of the problem concerning the structure of the game and its associated cost functions. Many of the problem variants are NP-hard, though we do identify several versions of the games that are solvable in polynomial time. We then investigate existence and the price of anarchy of pure Nash equilibria in k-splittable congestion games with linear costs. A k-splittable congestion game is one in which each player may split its flow on at most k different paths. We identify conditions for the existence of equilibria by providing a series of potential functions. For the price of anarchy, we show an asymptotic lower bound of 2.4 for unweighted k-splittable congestion games and 2.401 for weighted k-splittable congestion games, and an upper bound of 2.618 in both cases.
In this thesis we examine four network flow problems arising in the study of transportation, communication, and water networks. The first of these problems is the Integer Equal Flow problem, a network flow variant in which some arcs are restricted to carry equal amounts of flow. Our main contribution is that this problem is not approximable within a factor of 2n(1-epsilon]), for any fixed [epsilon] > 0, where n is the number of nodes in the graph. We extend this result to a number of variants on the size and structure of the arc sets. We next study the Pup Matching problem, a truck routing problem where two commodities ('pups') traversing an arc together in the network incur the arc cost only once. We propose a tighter integer programming formulation for this problem, and we address practical problems that arise with implementing such integer programming solutions. Additionally, we provide approximation and exact algorithms for special cases of the problem where the number of pups is fixed or the total cost in the network is bounded. Our final two problems are on the topic of congestion games, which were introduced in the area of communications networks.
by Carol Meyers.
Ph.D.
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Lubin, Miles (Miles C. ). "Mixed-integer convex optimization : outer approximation algorithms and modeling power." Thesis, Massachusetts Institute of Technology, 2017. http://hdl.handle.net/1721.1/113434.
Full textAbstract:
Thesis: Ph. D., Massachusetts Institute of Technology, Sloan School of Management, Operations Research Center, 2017.This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections.
Cataloged from student-submitted PDF version of thesis.
Includes bibliographical references (pages 137-143).
In this thesis, we study mixed-integer convex optimization, or mixed-integer convex programming (MICP), the class of optimization problems where one seeks to minimize a convex objective function subject to convex constraints and integrality restrictions on a subset of the variables. We focus on two broad and complementary questions on MICP. The first question we address is, "what are efficient methods for solving MICP problems?" The methodology we develop is based on outer approximation, which allows us, for example, to reduce MICP to a sequence of mixed-integer linear programming (MILP) problems. By viewing MICP from the conic perspective of modern convex optimization as defined by Ben-Tal and Nemirovski, we obtain significant computational advances over the state of the art, e.g., by automating extended formulations by using disciplined convex programming. We develop the first finite-time outer approximation methods for problems in general mixed-integer conic form (which includes mixed-integer second-order-cone programming and mixed-integer semidefinite programming) and implement them in an open-source solver, Pajarito, obtaining competitive performance with the state of the art. The second question we address is, "which nonconvex constraints can be modeled with MICP?" This question is important for understanding both the modeling power gained in generalizing from MILP to MICP and the potential applicability of MICP to nonconvex optimization problems that may not be naturally represented with integer variables. Among our contributions, we completely characterize the case where the number of integer assignments is bounded (e.g., mixed-binary), and to address the more general case we develop the concept of "rationally unbounded" convex sets. We show that under this natural restriction, the projections of MICP feasible sets are well behaved and can be completely characterized in some settings.
by Miles Lubin.
Ph. D.
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Farahat, Amr 1973. "Tractability through approximation : a study of two discrete optimization problems." Thesis, Massachusetts Institute of Technology, 2004. http://hdl.handle.net/1721.1/28857.
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Thesis (Ph. D.)--Massachusetts Institute of Technology, Sloan School of Management, Operations Research Center, 2004.Includes bibliographical references.
(cont.) algorithm, at one extreme, and complete enumeration, at the other extreme. We derive worst-case approximation guarantees on the solution produced by such an algorithm for matroids. We then define a continuous relaxation of the original problem and show that some of the derived bounds apply with respect to the relaxed problem. We also report on a new bound for independence systems. These bounds extend, and in some cases strengthen, previously known results for standard best-in greedy.
This dissertation consists of two parts. In the first part, we address a class of weakly-coupled multi-commodity network design problems characterized by restrictions on path flows and 'soft' demand requirements. In the second part, we address the abstract problem of maximizing non-decreasing submodular functions over independence systems, which arises in a variety of applications such as combinatorial auctions and facility location. Our objective is to develop approximate solution procedures suitable for large-scale instances that provide a continuum of trade-offs between accuracy and tractability. In Part I, we review the application of Dantzig-Wolfe decomposition to mixed-integer programs. We then define a class of multi-commodity network design problems that are weakly-coupled in the flow variables. We show that this problem is NP-complete, and proceed to develop an approximation/reformulation solution approach based on Dantzig-Wolfe decomposition. We apply the ideas developed to the specific problem of airline fleet assignment with the goal of creating models that incorporate more realistic revenue functions. This yields a new formulation of the problem with a provably stronger linear programming relaxation, and we provide some empirical evidence that it performs better than other models proposed in the literature. In Part II, we investigate the performance of a family of greedy-type algorithms to the problem of maximizing submodular functions over independence systems. Building on pioneering work by Conforti, Cornu6jols, Fisher, Jenkyns, Nemhauser, Wolsey and others, we analyze a greedy algorithm that incrementally augments the current solution by adding subsets of arbitrary variable cardinality. This generalizes the standard best-in greedy
by Amr Farahat.
Ph.D.
39
Schrödl, Stefan J. "Operator valued reproducing kernels and their application in approximation and statistical learning." Aachen Shaker, 2009. http://d-nb.info/99654559X/04.
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Hildebrandt, Klaus [Verfasser]. "Discretization and approximation of the shape operator, the Laplace-Beltrami operator, and the Willmore energy of surfaces / Klaus Hildebrandt." Berlin : Freie Universität Berlin, 2013. http://d-nb.info/1031106448/34.
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Hocine, Farida. "Approximation spectrale d'opérateurs." Saint-Etienne, 1993. http://www.theses.fr/1993STET4007.
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Il est bien connu que la convergence fortement stable est une condition suffisante de convergence des éléments spectraux approchées, i. E. Les valeurs propres non nulles, isolées et de multiplicité algébrique finie et les sous-espaces invariants maximaux qui leur sont associés, d'opérateurs linéaires bornés définis sur des espaces de Banach complexes. Dans ce travail, nous commençons par proposer une nouvelle notion de convergence : la convergence spectrale, que l'on montre être une condition nécessaire de convergence fortement stable et suffisante de convergence des éléments spectraux approchés. Nous donnons ensuite des conditions suffisantes de convergence spectrale moins restrictives que celles habituellement utilisées. Nous montrons également la convergence de quelques schémas de raffinement itératif pour l'approximation des bases de sous-espaces invariants maximaux, dans le cadre des méthodes de Newton inexactes et des séries de Rayleigh-Schrodinger, sous certaines des conditions suffisantes de convergence spectrale proposées. Nous donnons ensuite les résultats de quelques essais numériques
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Gaim, Wolfgang [Verfasser]. "Higher Order Semiclassical Approximations for Hamiltonians with Operator-Valued Symbols / Wolfgang Gaim." Tübingen : Universitätsbibliothek Tübingen, 2021. http://d-nb.info/1235399141/34.
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Lee, Howoo. "A diffusion approximation for multi-server finite-capacity bulk queues /." The Ohio State University, 1986. http://rave.ohiolink.edu/etdc/view?acc_num=osu1487265143146895.
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Karlsson, Ulf. "Semi-classical approximations of Quantum Mechanical problems." Doctoral thesis, KTH, Mathematics, 2002. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-3440.
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Alekseev, Vadim [Verfasser], Andreas [Gutachter] Thom, Thomas [Gutachter] Schick, and Alain [Gutachter] Valette. "Groups, operator algebras and approximation / Vadim Alekseev ; Gutachter: Andreas Thom, Thomas Schick, Alain Valette." Dresden : Technische Universität Dresden, 2021. http://nbn-resolving.de/urn:nbn:de:bsz:14-qucosa2-761277.
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Schell, Kevin E. "Virtual pooling approximation using longest path network optimization." Thesis, Massachusetts Institute of Technology, 2018. http://hdl.handle.net/1721.1/118702.
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Thesis: S.M., Massachusetts Institute of Technology, Department of Mechanical Engineering, in conjunction with the Leaders for Global Operations Program at MIT, 2018.Thesis: M.B.A., Massachusetts Institute of Technology, Sloan School of Management, in conjunction with the Leaders for Global Operations Program at MIT, 2018.
Cataloged from PDF version of thesis.
Includes bibliographical references (pages 94-95).
Abstract This thesis proposes a network swapping mechanism to approximate a virtual finished goods inventory pool under the constraint of fragmented commercial channel ownership. Globally, Caterpillar sells its product through a network of independently owned dealers which own their equipment inventory. These dealers are selling a product which has significant configuration complexity, a high coefficient of variation in demand, and long factory lead times - these three factors conspire to create a situation in which dealers must either maintain high levels of on-hand inventory or sacrifice customer service level. Virtual pooling can be a powerful technique for reducing held inventory and improving customer service level. In such a system, physical inventory is maintained in multiple locations, but a strong transshipment network allows inventory to be continuously rebalanced and effectively managed as a single pool. At Caterpillar, however, this is constrained by the fact that dealers are unwilling to unilaterally give up equipment that they own and which represents a potential sale, even if that equipment could be more effectively used by another dealer. This thesis proposes that a robust dealer swapping network that allows for multilateral swaps can generate universally beneficial inventory movement which lowers inventory and accelerates sales across the network. The mathematical formulation of this problem involves solving a longest path problem over a suitably defined network. In order to demonstrate the efficacy of this technique, a commercial network model was developed which allows for the simulation of multi-period equipment ordering, inventory management, and sales across a sample dealer network with and without network swapping implemented. Baseline simulation results conducted for a single vehicle class (Medium Wheel Loaders) suggest that network swapping has the potential to reduce on-hand inventory by more than 12% and decrease customer back orders by more than 17%. The swapping mechanism yields an NPV uplift of approximately USD 3 to 4M to the dealer network. This thesis concludes by proposing important extensions of the work conducted in this thesis to improve the practicality and financial impact of the proposed network swapping system.
by Kevin E. Schell.
S.M.
M.B.A.
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Escande, Paul. "Compression et inférence des opérateurs intégraux : applications à la restauration d’images dégradées par des flous variables." Thesis, Toulouse, ISAE, 2016. http://www.theses.fr/2016ESAE0020/document.
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Le problème de restauration d'images dégradées par des flous variables connaît un attrait croissant et touche plusieurs domaines tels que l'astronomie, la vision par ordinateur et la microscopie à feuille de lumière où les images sont de taille un milliard de pixels. Les flous variables peuvent être modélisés par des opérateurs intégraux qui associent à une image nette u, une image floue Hu. Une fois discrétisé pour être appliqué sur des images de N pixels, l'opérateur H peut être vu comme une matrice de taille N x N. Pour les applications visées, la matrice est stockée en mémoire avec un exaoctet. On voit apparaître ici les difficultés liées à ce problème de restauration des images qui sont i) le stockage de ce grand volume de données, ii) les coûts de calculs prohibitifs des produits matrice-vecteur. Ce problème souffre du fléau de la dimension. D'autre part, dans beaucoup d'applications, l'opérateur de flou n'est pas ou que partialement connu. Il y a donc deux problèmes complémentaires mais étroitement liés qui sont l'approximation et l'estimation des opérateurs de flou. Cette thèse a consisté à développer des nouveaux modèles et méthodes numériques permettant de traiter ces problèmesThe restoration of images degraded by spatially varying blurs is a problem of increasing importance. It is encountered in many applications such as astronomy, computer vision and fluorescence microscopy where images can be of size one billion pixels. Variable blurs can be modelled by linear integral operators H that map a sharp image u to its blurred version Hu. After discretization of the image on a grid of N pixels, H can be viewed as a matrix of size N x N. For targeted applications, matrices is stored with using exabytes on the memory. This simple observation illustrates the difficulties associated to this problem: i) the storage of a huge amount of data, ii) the prohibitive computation costs of matrix-vector products. This problems suffers from the challenging curse of dimensionality. In addition, in many applications, the operator is usually unknown or only partially known. There are therefore two different problems, the approximation and the estimation of blurring operators. They are intricate and have to be addressed with a global overview. Most of the work of this thesis is dedicated to the development of new models and computational methods to address those issues
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Xu, Guanglin. "Optimization under uncertainty: conic programming representations, relaxations, and approximations." Diss., University of Iowa, 2017. https://ir.uiowa.edu/etd/5881.
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In practice, the presence of uncertain parameters in optimization problems introduces new challenges in modeling and solvability to operations research. There are three main paradigms proposed for optimization problems under uncertainty. These include stochastic programming, robust optimization, and sensitivity analysis. In this thesis, we examine, improve, and combine the latter two paradigms in several relevant models and applications. In the second chapter, we study a two-stage adjustable robust linear optimization problem in which the right-hand sides are uncertain and belong to a compact, convex, and tractable uncertainty set. Under standard and simple assumptions, we reformulate the two-stage problem as a copositive optimization program, which in turns leads to a class of tractable semidefinite-based approximations that are at least as strong as the affine policy, which is a well studied tractable approximation in the literature. We examine our approach over several examples from the literature and the results demonstrate that our tractable approximations significantly improve the affine policy. In particular, our approach recovers the optimal values of a class of instances of increasing size for which the affine policy admits an arbitrary large gap. In the third chapter, we leverage the concept of robust optimization to conduct sensitivity analysis of the optimal value of linear programming (LP). In particular, we propose a framework for sensitivity analysis of LP problems, allowing for simultaneous perturbations in the objective coefficients and right-hand sides, where the perturbations are modeled in a compact, convex, and tractable uncertainty set. This framework unifies and extends multiple approaches for LP sensitivity analysis in the literature and has close ties to worst-case LP and two-stage adjustable linear programming. We define the best-case and worst-case LP optimal values over the uncertainty set. As the concept aligns well with the general spirit of robust optimization, we denote our approach as robust sensitivity analysis. While the best-case and worst-case optimal values are difficult to compute in general, we prove that they equal the optimal values of two separate, but related, copositive programs. We then develop tight, tractable conic relaxations to provide bounds on the best-case and worst case optimal values, respectively. We also develop techniques to assess the quality of the bounds, and we validate our approach computationally on several examples from—and inspired by—the literature. We find that the bounds are very strong in practice and, in particular, are at least as strong as known results for specific cases from the literature. In the fourth chapter of this thesis, we study the expected optimal value of a mixed 0-1 programming problem with uncertain objective coefficients following a joint distribution. We assume that the true distribution is not known exactly, but a set of independent samples can be observed. Using the Wasserstein metric, we construct an ambiguity set centered at the empirical distribution from the observed samples and containing all distributions that could have generated the observed samples with a high confidence. The problem of interest is to investigate the bound on the expected optimal value over the Wasserstein ambiguity set. Under standard assumptions, we reformulate the problem into a copositive programming problem, which naturally leads to a tractable semidefinite-based approximation. We compare our approach with a moment-based approach from the literature for two applications. The numerical results illustrate the effectiveness of our approach.
Finally, we conclude the thesis with remarks on some interesting open questions in the field of optimization under uncertainty. In particular, we point out that some interesting topics that can be potentially studied by copositive programming techniques.
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