Thesis (Ph.D.)--University of Delaware, 2007. / Principal faculty advisor: Errol L. Lloyd, Dept. of Computer & Info Sciences. Includes bibliographical references.

Made available in DSpace on 2014-06-12T15:49:50Z (GMT). No. of bitstreams: 1 license.txt: 1748 bytes, checksum: 8a4605be74aa9ea9d79846c1fba20a33 (MD5) Previous issue date: 2009 / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / O presente trabalho é baseada em dois aspectos fundamentais: (i) o estudo de procedimentos de normalização para sistemas de provas, especialmente para a lógica clássica com dedução natural; e (ii) a investigação de técnicas da perspectiva geométrica aplicadas em propriedades da teoria da prova. Com isso, a motivação específica deste trabalho reside principalmente na análise daqueles trabalhos que estão voltados à definição de técnicas da normalização através de mecanismos da perspectiva geométrica. Destaca-se que técnicas da perspectiva geométrica trazem o uso de arcabouços gráficos e/ou topológicos com a finalidade de representar sistemas formais de provas e suas propriedades. Dessa forma, a primeira parte do documento apresenta o uso de técnicas e arcabouços topológicos para estabelecer algumas propriedades, como, por exemplo, o critério de corretude e a normalização de sistemas de prova. Ao passo que a segunda parte do documento é inicialmente direcionada à descrição de algumas abordagens de normalização (principalmente) para a lógica clássica com dedução natural. E o complemento da segunda parte é dedicado à definição do principal objetivo do trabalho, i.e., desenvolver um procedimento de normalização para o conjunto completo de operadores dos N-Grafos, através do auxílio de algumas técnicas de perspectiva geométrica. (Destaca-se que as técnicas de perspectiva geométrica, aplicadas à normalização dos N-Grafos, não fazem uso de arcabouços topológicos). N-Grafos é um sistema de prova com múltipla conclusão definido para lógica clássica proposicional com dedução natural. Ademais, os N-Grafos possuem tanto regras lógicas como estruturais, estruturas cíclicas são permitidas e além disso as derivações são representadas como grafos direcionados. De fato, a princpal característica do procedimento de normalização aqui apresentado é fornecer um tratamento completo para as estruturas cíclicas. Ou seja, são definidas classes de ciclos válidos, critério de corretude, propriedades e ainda um algoritmo específico para normalizar os ciclos nos N-Grafos. Destaca-se que esses elementos são construídos através do auxílio de arcabouços gráficos. Além disso, o mecanismo de normalização é capaz de lidar com os diferentes papéis executados pelos operadores ?/>. Adicionalmente, apresenta-se uma prova direta da normalização fraca para os N-Grafos, bem como, a determinação das propriedades da subfórmula e da separação

<p>This PhD thesis, consisting of an introduction, four papers, and some supplementary results, studies the problem of finding an <i>optimal realization</i> of a given finite metric space: a weighted graph which preserves the metric's distances and has minimal total edge weight. This problem is known to be NP-hard, and solutions are not necessarily unique.</p><p>It has been conjectured that <i>extremally weighted</i> optimal realizations may be found as subgraphs of the <i>hereditarily optimal realization</i> Γ_d, a graph which in general has a higher total edge weight than the optimal realization but has the advantages of being unique, and possible to construct explicitly via the <i>tight span</i> of the metric.</p><p>In Paper I, we prove that the graph Γ_d is equivalent to the 1-skeleton of the tight span precisely when the metric considered is <i>totally split-decomposable</i>. For the subset of totally split-decomposable metrics known as <i>consistent</i> metrics this implies that Γ_d is isomorphic to the easily constructed <i>Buneman graph</i>.</p><p>In Paper II, we show that for any metric on at most five points, any optimal realization can be found as a subgraph of Γ_d.</p><p>In Paper III we provide a series of counterexamples; metrics for which there exist extremally weighted optimal realizations which are not subgraphs of Γ_d. However, for these examples there also exists at least one optimal realization which is a subgraph.</p><p>Finally, Paper IV examines a weakened conjecture suggested by the above counterexamples: can we always find some optimal realization as a subgraph in Γ_d? Defining <i>extremal</i> optimal realizations as those having the maximum possible number of shortest paths, we prove that any embedding of the vertices of an extremal optimal realization into Γ_d is injective. Moreover, we prove that this weakened conjecture holds for the subset of consistent metrics which have a 2-dimensional tight span</p>

This PhD thesis, consisting of an introduction, four papers, and some supplementary results, studies the problem of finding an optimal realization of a given finite metric space: a weighted graph which preserves the metric's distances and has minimal total edge weight. This problem is known to be NP-hard, and solutions are not necessarily unique. It has been conjectured that extremally weighted optimal realizations may be found as subgraphs of the hereditarily optimal realization Γd, a graph which in general has a higher total edge weight than the optimal realization but has the advantages of being unique, and possible to construct explicitly via the tight span of the metric. In Paper I, we prove that the graph Γd is equivalent to the 1-skeleton of the tight span precisely when the metric considered is totally split-decomposable. For the subset of totally split-decomposable metrics known as consistent metrics this implies that Γd is isomorphic to the easily constructed Buneman graph. In Paper II, we show that for any metric on at most five points, any optimal realization can be found as a subgraph of Γd. In Paper III we provide a series of counterexamples; metrics for which there exist extremally weighted optimal realizations which are not subgraphs of Γd. However, for these examples there also exists at least one optimal realization which is a subgraph. Finally, Paper IV examines a weakened conjecture suggested by the above counterexamples: can we always find some optimal realization as a subgraph in Γd? Defining extremal optimal realizations as those having the maximum possible number of shortest paths, we prove that any embedding of the vertices of an extremal optimal realization into Γd is injective. Moreover, we prove that this weakened conjecture holds for the subset of consistent metrics which have a 2-dimensional tight span

Topology-related issues are becoming increasingly important in Computer Graphics. This research examines the use of topological analysis for solving two important problems in 3D Graphics: surface parameterization, and vector field design on surfaces. Many applications, such as high-quality and interactive image synthesis, benefit from the solutions to these problems. Surface parameterization refers to segmenting a 3D surface into a number of patches and unfolding them onto a plane. A surface parameterization allows surface properties to be sampled and stored in a texture map for high-quality and interactive display. One of the most important quality measurements for surface parameterization is stretch, which causes an uneven sampling rate across the surface and needs to be avoided whenever possible. In this thesis, I present an automatic parameterization technique that segments the surface according to the handles and large protrusions in the surface. This results in a small number of large patches that can be unfolded with relatively little stretch. To locate the handles and large protrusions, I make use of topological analysis of a distance-based function on the surface. Vector field design refers to creating continuous vector fields on 3D surfaces with control over vector field topology, such as the number and location of the singularities. Many graphics applications make use of an input vector field. The singularities in the input vector field often cause visual artifacts for these applications, such as texture synthesis and non-photorealistic rendering. In this thesis, I describe a vector field design system for both planar domains and 3D mesh surfaces. The system provides topological editing operations that allow the user to control the number and location of the singularities in the vector field. For the system to work for 3D meshes surface, I present a novel piecewise interpolating scheme that produces a continuous vector field based on the vector values defined at the vertices of the mesh. I demonstrate the effectiveness of the system through several graphics applications: painterly rendering of still images, pencil-sketches of surfaces, and texture synthesis.

The problem of defining cycles in infinite graphs has received much attention in the literature. Diestel and Kuhn have proposed viewing a graph as 1-complex, and defining a topology on the point set of the graph together with its ends. In this setting, a circle in the graph is a homeomorph of the unit circle S^1 in this topological space. For locally finite graphs this setting appears to be natural, as many classical theorems on cycles in finite graphs extend to the infinite setting. A Hamilton circle in a graph is a circle containing all the vertices of the graph. We exhibit a necessary and sufficient condition that a countable graph contain a Hamilton circle in terms of the existence of Hamilton cycles in an increasing sequence of finite graphs. As corollaries, we obtain extensions to locally finite graphs of Zhan's theorem that all 7-connected line graphs are hamiltonian (confirming a conjecture of Georgakopoulos), and Ryjacek's theorem that all 7-connected claw-free graphs are hamiltonian. A third corollary of our main result is Georgakopoulos' theorem that the square of every two-connected locally finite graph contains a Hamilton circle (an extension of Fleischner's theorem that the square of every two-connected finite graph is Hamiltonian).