Browsing Doctoral Dissertations by Title
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Dražić, Zorica (Beograd , 2014)[more][less]
Abstract: The Variable neighborhood search method proved to be very successful for solving discrete and continuous optimization problems. The basic idea is a systematic change of neighborhood structures in search for the better solution. For optimiza- tion of multiple variable functions, methods for obtaining the local minimum starting from certain initial point are used. In case when the continuous function has many local minima, nding the global minimum is usually not an easy task since the obta- ined local minima in most cases are not optimal. In typical implementations with bounded neighborhoods of various diameters it is not possible, from arbitrary point, to reach all points in solution space. Consequently, the strategy of using the nite number of neighborhoods is suitable for problems with solutions belonging to some known bounded subset of IRn. In order to overcome the previously mentioned limitation the new variant of the method is proposed, Gaussian Variable neighborhood search method. Instead of de ning the sequence of di erent neighborhoods from which the random point will be chosen, all neighborhoods coincide with the whole solution space, but with di e- rent probability distributions of Gaussian type. With this approach, from arbitrary point another more distant point is theoretically reachable, although with smaller probability. In basic version of Variable neighborhood search method one must de ne in advance the neighborhood structure system, their number and size, as well as the type of random distribution to be used for obtaining the random point from it. Gaussian Variable neighborhood search method has less parameters since all the neighborhoods are theoretically the same (equal to the solution space), and uses only one distribution family - Gaussian multivariate distribution with variable dispersion. File transfer scheduling problem (FTSP) is an optimization problem widely appli- cable to many areas such as Wide Area computer Networks (WAN), Local Area Ne- v tworks (LAN), telecommunications, multiprocessor scheduling in a MIMD machines, task assignments in companies, etc. As it belongs to the NP-hard class of problems, heuristic methods are usually used for solving this kind of problems. The problem is to minimize the overall time needed to transfer all les to their destinations for a given collection of various sized les in a computer network, i.e. to nd the le transfer schedule with minimal length. In order to obtain the exact solution of the FTS problem, integer linear pro- gramming formulations are proposed and their correctness is proved. In this way optimal solutions can be found for small and medium size test instances. For large test instances, the Variable neighborhood search method is proposed using the "permutation" representation and typical neighborhood structures. More- over, the same method is used for obtaining the upper bounds of the solutions which are used in proposed integer linear programming formulations. For obtaining be- tter solutions in the small neighborhood of the current solution, three di erent local search procedures are implemented: 2-swap, 2-swap adjacent and variable neighbo- rhood descent. In order to apply the continuous optimization methods for solving FTSP, the weighted solution representation is developed. Such representation enables the co- ntinuous optimization methods to be used, which do not require the di erentiability of objective function. Since Gauss Variable neighborhood search method proved to be successful in continuous optimization problems, it was applied to FTSP. Pre- viously described local search procedures can also be used with weighted solution representation. Using the proposed methods optimal solutions for all small and medium size test instances are found. For large size instances, which are beyond the reach of exact methods, metaheuristic methods obtained good solutions in reasonable time. URI: http://hdl.handle.net/123456789/4246 Files in this item: 1
phdDrazic_Zorica.pdf ( 4.739Mb ) -
Mihajlović, Borivoje (Belgrade , 1964)[more][less]
URI: http://hdl.handle.net/123456789/227 Files in this item: 1
phdBorivojeMihajlovic.pdf ( 2.509Mb ) -
Manojlović, Vesna (Beograd , 2008)[more][less]
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Nikolić, Silvana (Belgrade)[more][less]
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Marjanović, Miroslav (Belgrade)[more][less]
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Kamberi, Qerim (Priština)[more][less]
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Tanasijević, Ivana (Beograd , 2020)[more][less]
Abstract: The motivation for writing this doctoral dissertation is a multimedia col-lection that is the result of many years of field research conducted by researchers from the Institute for Balkan studies of the Serbian Academy of Sciences and Arts. The collection consists of materials in the form of recorded interviews, various recorded customs, associated textual descriptions (protocols) and numerous other documents.The subject of research of this dissertation is the study of possibilities and the development of new methods that could be used as a starting point in solving the problem of managing the intangible cultural heritage of the Balkans. The subtasksthat emerge in this endeavor are the development of adequate design and implemen-tation of a multimedia database of intangible cultural heritage that would meet the needs of different types of users, automatic semantic annotation of protocols using natural language processing methods, as a basis for semi-automatic annotation of the multimedia collection, and successful search by metadata which comply with the CIDOC CRM standard, study of additional search possibilities of this collection in order to gain new knowledge, as well as development of selected methods.The main problem with the available methods is that there is still not enough developed infrastructure in the context of natural language processing, organization and management in the field of cultural heritage in the Balkans and especially for the Serbian language, which could be effectively used to solve the proposed problem.There is thus a strong need to develop methods to reach an appropriate solution.For the semi-automatic annotation of multimedia materials, automatic semantic annotation of the protocols associated with the materials was used. It was carriedout by methods of information extraction, recognition of named entities and topicextraction, using rule-based techniques with the help of additional resources suchas electronic dictionaries, thesauri and vocabularies from a specific domain.To classify textual protocols in relation to the topic, research was conducted onmethods that can be used to solve the problem of classifying texts in the Serbianlanguage, and a method was offered that is adapted to the specific domain beingprocessed (intangible cultural heritage), to the specific problems being solved (clas-sification of protocols in relation to the topic) and to the Serbian language, as one of the morphologically rich languages.To work with spatial data, a spatial model has been developed that is suitable for displaying results on a map, as well as for creating spatial queries through an interactive graphical display of a map of locations.The results of experiments conducted on the developed methods show that the use of a rule-based approach in combination with additional language resources an dwith putting in a reasonable amount of effort gives very good results for the task of information extraction. An F measure of 0.87 was reached for the extraction of named entities, while an F measure of 0.90 was reached for the extraction of topics,which is in the range of measures from published research from similar problem sand domains.The results of the text classification indicate that the selected statistical methods of machine learning in their basic form when applied to the protocols, although generally successful, give a bad F measure, 0.44, while significant improvement is achieved with the use of semantic techniques, in which case an F measure of 0.88 is reached.Some of the results presented in this dissertation are contained in the papers[266], [265], [94], [264], [267], which have been published or accepted for publication.The conclusion drawn from the research is that to solve the given problem it is necessary to engage experts from several fields, that the needs of different groups of users are complex, which complicates the task of organizing and managing them ultimedia collection, that the domain of cultural heritage is very rich in semantics,that context plays a major role in the tasks of information extraction and text classification, and finally that for these tasks the developed rule-based methods of natural language processing as well as statistical techniques of machine learning prove to be successful. URI: http://hdl.handle.net/123456789/5093 Files in this item: 1
IvanaTanasijevicdr.pdf ( 4.674Mb ) -
Džamić, Dušan (Beograd , 2021)[more][less]
Abstract: The theory of complex networks has proven to be very important inthe study of the characteristics and structure of various complex systems. In thelast two decades, a large number of researches have been directed towards thedevelopment of methods for clustering in complex networks. In 2012, Center forDiscrete Mathematics and Theoretical Computer Science (DIMACS), which is awell-known consortium of prestigious academic institutions (Rutgers University,Princeton, Colombia) and research laboratories (Microsoft, IBM, AT & T, NEC),included the problem of clustering in complex networks on the list of the mostimportant problems and challenges in computer science. Clustering in complexnetworks can be applied in a variety of contexts to achieve different goals, andtherefore, there is no generally accepted definition of a cluster. For this reason,different approaches are used in developing clustering methods. An approach thathas attracted the most attention of researchers involves two subproblems: defininga function to determine the quality of a partition and constructing methods to finda partition that has the maximum value of the defined quality function. In thisapproach, the problem of clustering is formulated as the problem of combinatorialoptimization and various methods of mathematical optimization can be used tosolve it. One of the most commonly used quality function is the modularity.Clustering by modularity maximization, i.e., finding a partition with the max-imum value of modularity, is NP-hard problem. Thus, only heuristic algorithmsare suitable of processing large datasets. In this dissertation, a novel method formodularity maximization based on the variable neighborhood search heuristic isproposed. For the purpose of efficient application in large-scale complex networks,a procedure for decomposition of the problem into smaller subproblems is devel-oped. In addition, a mechanism for overcoming local maxima of modularity isimproved using criteria for occasional acceptance of solution which is worse thanthe current one. DIMACS instances are used to test the proposed method, and theobtained results are compared with the best ones presented in the literature, ob-tained by two methods developed in DIMACS implementation challenge in 2012.In addition, the obtained results are compared with the results of six methodsdeveloped after 2012, from the literature. A comparative analysis of the resultsshows that the proposed method outperforms the existing methods for modularitymaximization and improves the best known solutions on 9 out of 13 hard instances. Clustering by modularity maximization is not suitable for detecting small clus-ters in large networks. For this reason, a new function for measuring the qualityof a partition has been proposed in the dissertation. Through three theorems, itis shown that the new measure, called E-function, has the potential to identifyclusters in the network and overcome limits of modularity. For testing the pro-posed E-function and comparison with the modularity function, a generic variableneighborhood method is developed to optimize the considered quality function.Computational experiments are performed on generated and real instances fromthe literature for which the correct division into clusters is known. The resultsshow that the expected clusters can be identified, both on artificial and real in-stances, by maximizing the E-function. URI: http://hdl.handle.net/123456789/5214 Files in this item: 1
teza_dzamic.pdf ( 3.074Mb ) -
Janković, Slobodan (Beograd , 1979)[more][less]
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Marković, Marijan (Belgrade , 2013)[more][less]
Abstract: This work consists of three chapters. The first one contains some well known facts about Hardy classes of harmonic, analytic, and logarithmically subharmonic functions in the unit disk, as well as their applications. Then we briefly talk about the harmonic and minimal surfaces, the classical isoperimetric inequality, and the more recent results related to this inequality. One of the most elegant way to establish the isoperimetric inequality is via Carleman’s inequality for analytic functions in disks. In the second chapter we present the results from our recent work [29] for harmonic mappings of a disc onto a Jordan surface. In this chapter we establish the versions of classical theorems of Carath´eodory and Smirnov for mappings of the previous type. At the end of the head we apply these results to prove the isoperimetric inequality for Jordan harmonic surfaces bounded by rectifiable curves. In the third chapter, according to the author paper [35], we prove an inequality of the isoperimetric type, similar to Carleman’s, for functions of several variables. The first version of this inequality is for analytic functions in a Reinhardt domain. The second one concerns the functions that belong to Hardy spaces in polydiscs. URI: http://hdl.handle.net/123456789/2586 Files in this item: 1
Markovic_Marijan.pdf ( 709.3Kb ) -
Lazarević, Milan (Beograd , 2020)[more][less]
Abstract: ist of already known and recently established Cauchy-Schwarz inequalities fore lementary operators,σ-elementary transformers and inner product type transformers iscomplemented by the next variant of Cauchy-Schwarz inequality in Schatten-von Neumann ideals: ZΩAtA∗tdμ(t) 12q−12ZΩAtXBtdμ(t) ZΩB∗tBtdμ(t) 12r−12p6 ZΩA∗tAtdμ(t) 12qX ZΩBtB∗tdμ(t) 12rpfor allX2Cp(H)and for allp, q, r>1which satisfies2p=1q+1r,if families of operatorsfAtgt∈Ω,fA∗tgt∈Ω,fBtgt∈Ω,fB∗tgt∈Ωare strongly square integrabile, such thatRΩAtA∗tdμ(t)andRΩB∗tBtdμ(t)are (boundedly) invertible operators.Enabled by some additional conditions of commutativity and normality for operator fami-liesfAng∞n=1,fBng∞n=1,fAtgt∈ΩandfBtgt∈Ω,as well as by the degree ofp-modifications ofunitary invariant norms, some others variants of those inequalities will also be considered,including their applications to the certain problems in operator theory, norm inequalities forgeneralized function derivations of Pick operator values functions and operator values Fouriertransformations of complex measures, as well as some Grüss-Landau type inequalities. URI: http://hdl.handle.net/123456789/5092 Files in this item: 1
disertacija_Lazarevic_Milan_dorada.pdf ( 1.868Mb ) -
Kovačević, Ilija (Belgrade)[more][less]
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Gilezan, Koriolan (Belgrade)[more][less]
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Jovanović, Boško (Belgrade)[more][less]
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Hoxha, Isak (Priština)[more][less]
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Mihajlović, Bojana (Beograd , 2016)[more][less]
Abstract: The subject of this dissertation belongs to scientific field of spectral graph theory, a young branch of mathematical combinatorics, i.e. graph theory, which finds important applications in many areas, such as chemistry, physics, computer science, telecommunications, sociology, etc., and various fields of mathematics. Spectral graph theory connects basic properties and the structure of a graph with characteristics of the spectra of its matrices (adjacency matrix, Laplacian matrix, etc.). In this dissertation we only work with the adjacency matrix. The second largest eigenvalue of the adjacency matrix of a graph (or, simply, second largest eigenvalue of a graph), as well as its distance from the largest eigenvalue, are very important especially in applications of spectral graph theory in computer science. The property of a graph that one of its eigenvalues does not exceed some given value is a hereditary one; therefore, many of the investigations of this kind have been directed at finding the maximal allowed graphs, or minimal forbidden graphs for that property. In this dissertation we determine some classes of graphs whose second largest eigenvalue does not exceed some given value, and, for that purpose, we develop some very useful tools. In methodological sense, investigations in this dissertation represent a combined approach consisting of application of the algebraic apparatus and methods of spectral graph theory and combinatorial reasoning, whilst at some stages the expert system newGRAPH has been used. The dissertation consists of eight chapters, each of which is divided into subchapters. In the beginning, some important previous work is shown, and afterwards we present some original elements of the algebraic and combinatorial apparatus that speed up and simplify the further work. We define some mappings between certain families of graphs, some of which preserve the sign of the expression 2 2 , and, using them, we describe and systematize some (already known) results in a new way. Further on we completely determine all maximal reflexive tricyclic cacti which are not RS-decidable and whose cycles do not form a bundle, from the classes 1 R and 3 R , and we give some partial results about the class 2 R , using previously induced mappings (until now only the graphs from the remaining class 4 R have been completely determined [40], [46]). Next, we completely describe all minimal forbidden graphs in the class of bicyclic graphs with a bridge, and all minimal forbidden graphs in the class 3 R - the approach that so far has never been used with reflexive graphs. Then we determine the maximal number of the cycles for RS-undecidable reflexive cacti whose cycles do form a bundle, and, therefore, generally for RS-undecidable reflexive cacti and we describe three classes of maximal reflexive RS-undecidable reflexive cacti that contain a bundle. Further on, some of the previous results are generalized: the generalized RS-theorem is stated and proved (so-called GRS-theorem) for any r , r 0 ; previously induced mappings are generalized, their properties are proved and various examples of classes of graphs with the property 2 r (for r 0 ) are given. Based on this, we describe all GRS-undecidable maximal graphs for the property 2 2 in the class of unicyclic and multicyclic graphs, and also all RS-undecidable maximal θ-graphs for this property as well as all GRS-undecidable maximal trees with the property 2 5 1 2 . Furthermore, we investigate the limit 3 (as in [28]) and we describe all trees with the diameter 3 and the diameter larger than 8, with the property 2 3 , as well as all GRSundecidable multicyclic cacti with the same property. Finally, we introduce and apply so-called σ-modifications of Smith trees. We describe seven σ-modifications and corresponding extensions, and we notice the appearance in (already known) results in the class of multicyclic reflexive cacti with 4 cycles. Applying some extensions to certain families of tricyclic cacti, we obtained the results in the class of multicyclic reflexive cacti with 4 cycles, using a different approach [48]. Finally, in the conclusion, we suggest some possible directions of further investigations. URI: http://hdl.handle.net/123456789/4445 Files in this item: 1
Mihailovic_Bojana.pdf ( 6.960Mb ) -
Acketa, Dragan (Novi Sad , 1984)[more][less]
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Vučemilović, Ante (Belgrade)[more][less]
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Cerović, Blagoje (Novi Sad , 1982)[more][less]
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Crvenković, Siniša (Novi Sad , 1981)[more][less]
Abstract: Teorija semigrupa razvija se kao samostalna °blast savremene algebre, Predmet izu6avanja teorije semigrupa su razne kiase semigrupa tj. semigrupe koje zadovoljavaju dati uslov. U ovom radu razmatramo semigrupe iz nekih podklasa kiase regularnih semigrupa. Pojam regularnosti, koji je uveo J. von Neumann [31] za prstene, su Thierrin i BarHep preneli u teoriju semigrupa 6to se pokazalo zna6ajnim za razvoj teorije semigrupa umAte. Ovde se posebno ispituje jedna podklasa kiase kompletno regularnih semigrupa tzv. klasa (m,n)*-anti-inverznih semigrupa. Ova klasa obuhvata klasu anti-inverznih semigrupa ill Pojam bazisne kiase, neke klase semigrupa, uveo je E.C. JThnHH [25]. U radu odredjujemo bazisne kiase za razne kiase semigrupa. Zna6ajnu klasu semigrupa 6ine polumr0e. P.M. Cohn [9] i C. Pe6aHe su 1965. godine pokazali da je svaka algebra podalgebra neke semigrupe. U Glavi IV opisujemo klasu algebri koje su podalgebre polumrea. U Glavi I su navedeni elementarni pojmovi o semigrupama, grupama, algebrama, idealima, kongruencijama, itd. Dati Virtual Library of Faculty of Mathematics - University of Belgrade elibrary.matf.bg.ac.rs ii su dokazi nekih teorema koje se koriste u radu. Ovaj materijal uzet je iz [7] i [22]. Takodje, dat je dokaz G. upone za teoremu Cohn-Pe6aHe. U Glavi II ispituju se (m,n)*-anti-inverzne semigrupe. Materijal ove glave preuzet je iz [ 61, [11] i [12]. U ta6ki 2. date su neke dekompozicije (m,n)*-anti-inverznih semigrupa. Teorema 2.3. glavni je rezultat ove glave. Green-ove relacije razmatraju se u ta6ki 3. Dobija se niz karakterizaci - ja semigrupa iz klase m,n . Na kraju Glave II navedena su tvrdjenja Eiji dokazi su izostavljeni jer su sli6ni dokazima teorema u [ 21. U Glavi III ispituju se bazisne klase raznih klasa semigrupa. Dat je algoritam kojim odredjujemo bazisnu klasu bilo koje klase (m,n)*-anti-inverznih semigrupa. Primeri bazisnih klasa za razne semigrupe dati su u ta6ki 2. Materim, n jal za take 1. i 2. uzet je iz [121. U ta6ki 3. razmatraju se QS* (OS ) semigrupe tj. semigrupe nje sve prave podsemi - m,n m,n grupe pripadaju klasi m,n (Sm,n ). Teoremom 3.1. data je karakterizacija semigrupa klase QS*m,n (QS m,n ). Problem egzistencije bazisne klase semigrupa ije sve prave podsemigrupe zadovoljavaju uslov oblika (Vx)(By)4)(x,y) re§en je u ta6ki 4. Na kraju 4. data je nekoliko primera. Materijal iz ta6aka 3. i 4. ovde je prvi put izloen. U Glavi IV opisane su podalgebre polumr0a. Potreban i dovoljan uslov da neka algebra bude podalgebra polumree dat je u taCki 1. Lema 1.3. je kljufta lema u dokazu teoreme 1.1. Virtual Library of Faculty of Mathematics - University of Belgrade elibrary.matf.bg.ac.rs iii Dokaz ove leme izvodi se koristedi pojam transformacije U tadki 2. navedeni su neki specijalni sludajevi koji su neposredna posledica teoreme 1.1. Materijal za ovu glavu uzet je iz [18]. Literatura koja je korigdena u ovom radu navedena je na kraju i 6ine je 44 bibliografske jedinice. Dr Stojan Bogdanovid svojim idejama i savetima pornogao mi je pri izradi ovog rada zbog 6eqa mu dugujem trajnu zahvalnost. Akademik profesor (op(- 11 HynoHa velikodugno je pristao na saradnju sa autorom ovog rada. Zahvaljujem se profesoru 6to je prihvatio moju saradnju i omogudio mi da rezultato zajedni6kocr rada izlo2im u Glavi IV. Profesor Svetozar Milid prihvatio se da bude mentor pri izradi ove disertacije. Imam prijatnu du2nost da se zahvalim profesoru Milidu za nesebi6nu pa2nju koju posvedije mom radu. URI: http://hdl.handle.net/123456789/4094 Files in this item: 1
Neke_klase_semigrupa.PDF ( 10.42Mb )