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Graphs
Kinds of Graphs Terms modified by Graphs Selected AbstractsELICITING A DIRECTED ACYCLIC GRAPH FOR A MULTIVARIATE TIME SERIES OF VEHICLE COUNTS IN A TRAFFIC NETWORKAUSTRALIAN & NEW ZEALAND JOURNAL OF STATISTICS, Issue 3 2007Catriona M. Queen Summary The problem of modelling multivariate time series of vehicle counts in traffic networks is considered. It is proposed to use a model called the linear multiregression dynamic model (LMDM). The LMDM is a multivariate Bayesian dynamic model which uses any conditional independence and causal structure across the time series to break down the complex multivariate model into simpler univariate dynamic linear models. The conditional independence and causal structure in the time series can be represented by a directed acyclic graph (DAG). The DAG not only gives a useful pictorial representation of the multivariate structure, but it is also used to build the LMDM. Therefore, eliciting a DAG which gives a realistic representation of the series is a crucial part of the modelling process. A DAG is elicited for the multivariate time series of hourly vehicle counts at the junction of three major roads in the UK. A flow diagram is introduced to give a pictorial representation of the possible vehicle routes through the network. It is shown how this flow diagram, together with a map of the network, can suggest a DAG for the time series suitable for use with an LMDM. [source] BONDSYM: SIMULINK-based educational software for analysis of dynamic systemCOMPUTER APPLICATIONS IN ENGINEERING EDUCATION, Issue 2 2010J.A. Calvo Abstract This article presents an educational software called BONDSYM developed to allow engineering students to learn easily and quickly about the analysis of dynamic systems through the Bond Graph method. This software uses the SIMULINK library of MATLAB, which has proven to be an excellent choice in order to implement and solve the dynamic equations involved. The application allows for the representation of the behavior of a dynamic system analyzed through the Bond Graph theory in order to understand the dynamic equations and the physical phenomena involved. Based on block diagram of SIMULINK, the different "bonds" of Bond Graph can be integrated as SIMULINK blocks in order to generate the dynamic model. A few simple models are analyzed through this application. © 2009 Wiley Periodicals, Inc. Comput Appl Eng Educ 18: 238,251, 2010; Published online in Wiley InterScience (www.interscience.wiley.com); DOI 10.1002/cae.20246 [source] Scene Graph and Frame Update Algorithms for Smooth and Scalable 3D Visualization of Simulated Construction OperationsCOMPUTER-AIDED CIVIL AND INFRASTRUCTURE ENGINEERING, Issue 4 2002Vineet R. Kamat One of the prime reasons inhibiting the widespread use of discrete-event simulation in construction planning is the absence of appropriate visual communication tools. Visualizing modeled operations in 3D is arguably the best form of communicating the logic and the inner working of simulation models and can be of immense help in establishing the credibility of analyses. New software development technologies emerge at incredible rates that allow engineers and scientists to create novel, domain-specific applications. The authors capitalized on a computer graphics technology based on the concept of the scene graph to design and implement a general-purpose 3D visualization system that is simulation and CAD-software independent. This system, the Dynamic Construction Visualizer, enables realistic visualization of modeled construction operations and the resulting products and can be used in conjunction with a wide variety of simulation tools. This paper describes the scene graph architecture and the frame updating algorithms used in designing the Dynamic Construction Visualizer. [source] Scheduling dense linear algebra operations on multicore processorsCONCURRENCY AND COMPUTATION: PRACTICE & EXPERIENCE, Issue 1 2010Jakub Kurzak Abstract State-of-the-art dense linear algebra software, such as the LAPACK and ScaLAPACK libraries, suffers performance losses on multicore processors due to their inability to fully exploit thread-level parallelism. At the same time, the coarse,grain dataflow model gains popularity as a paradigm for programming multicore architectures. This work looks at implementing classic dense linear algebra workloads, the Cholesky factorization, the QR factorization and the LU factorization, using dynamic data-driven execution. Two emerging approaches to implementing coarse,grain dataflow are examined, the model of nested parallelism, represented by the Cilk framework, and the model of parallelism expressed through an arbitrary Direct Acyclic Graph, represented by the SMP Superscalar framework. Performance and coding effort are analyzed and compared against code manually parallelized at the thread level. Copyright © 2009 John Wiley & Sons, Ltd. [source] Analysis by DC,EPG of the resistance to Bemisia tabaci on an Mi -tomato lineENTOMOLOGIA EXPERIMENTALIS ET APPLICATA, Issue 3 2001Y.X. Jiang Abstract The tomato Mi gene confers resistance to nematodes, Meloidogyne spp., and to the potato aphid, Macrosiphum euphorbiae (Thomas). Previous greenhouse choice assays with Bemisia tabaci (Gennadius) showed that tomato commercial varieties carrying this gene had significantly lower values of host suitability and whitefly reproduction than varieties lacking Mi. This indicated that Mi, or another gene in its region, could regulate partial resistance. In order to characterise this resistance, probing and feeding behaviour of Bemisia tabaci B-biotype was studied with DC Electrical Penetration Graph (EPG) technique on the near-isogenic tomato lines Moneymaker (without Mi) and Motelle (carrying Mi). Significant differences (P < 0.05) between tomato lines were found in EPG parameters related to epidermis and/or mesophyll tissues. On Motelle, a lower percentage of whiteflies achieved phloem phase and they made more probes before attaining first phloem phase, had a higher ratio (number of probes before first phloem phase)/(total number of probes), had a longer total duration of non-probing time, and a longer time before making the first intracellular puncture and before making the first phloem phase. In contrast, most of the parameters related to phloem phase were found not to differ significantly between these near-isogenic lines. The behavioural data strongly suggest that the partial resistance in the variety Motelle is due to factors in the epidermis and/or mesophyll that inhibit the whiteflies from reaching phloem sieve elements. However, once the stylets reach a sieve element, whitefly behaviour did not differ between the two varieties. Thus, phloem sap of the two varieties appears to be equally acceptable to the whiteflies. Further studies are necessary to provide a better understanding of these mechanisms of resistance to whiteflies in tomatoes. [source] Extension of Vedernikov's Graph for Seepage from CanalsGROUND WATER, Issue 2 2001Bhagu R. Chahar In this investigation, using previously derived equations by Vedernikov and Morel-Seytoux, closed-form solutions have been obtained to compute the seepage from a slit and a strip. Also, a graphical solution as an extension of Vedernikov's graph has been presented for computing quantity of seepage from triangular, rectangular, and trapezoidal canals. The solution replaces approximately the cumbersome evaluation of improper integrals with unknown implicit transformation variables. [source] Graph-based interaction in a fuzzy object oriented databaseINTERNATIONAL JOURNAL OF INTELLIGENT SYSTEMS, Issue 7 2001Gloria Bordogna In this paper, the definition of graph-based operations to select and browse a fuzzy object oriented database which manages both crisp and fuzzy information is proposed. The underlying data model is a fuzzy graph-based model (FOOD), previously defined by Bordogna et al., within fuzzy set theory and possibility theory. The evaluation mechanism of the graph-based operations is formalized in terms of graph transformations and fuzzy pattern matching. © 2001 John Wiley & Sons, Inc. [source] Nonlinear wave function expansions: A progress reportINTERNATIONAL JOURNAL OF QUANTUM CHEMISTRY, Issue 15 2007Ron Shepard Abstract Some recent progress is reported for a novel nonlinear expansion form for electronic wave functions. This expansion form is based on spin eigenfunctions using the Graphical Unitary Group Approach and the wave function is expanded in a basis of product functions, allowing application to closed and open shell systems and to ground and excited electronic states. Each product basis function is itself a multiconfigurational expansion that depends on a relatively small number of nonlinear parameters called arc factors. Efficient recursive procedures for the computation of reduced one- and two-particle density matrices, overlap matrix elements, and Hamiltonian matrix elements result in a very efficient computational procedure that is applicable to very large configuration state function (CSF) expansions. A new energy-based optimization approach is presented based on product function splitting and variational recombination. Convergence of both valence correlation energy and dynamical correlation energy with respect to the product function basis dimension is examined. A wave function analysis approach suitable for very large CSF expansions is presented based on Shavitt graph node density and arc density. Some new closed-form expressions for various Shavitt Graph and Auxiliary Pair Graph statistics are presented. © 2007 Wiley Periodicals, Inc. Int J Quantum Chem, 2007 [source] Graph-based tools for re-engineeringJOURNAL OF SOFTWARE MAINTENANCE AND EVOLUTION: RESEARCH AND PRACTICE, Issue 4 2002Katja Cremer Abstract Maintenance of legacy systems is a challenging task. Often, only the source code is still available, while design or requirements documents have been lost or have not been kept up-to-date with the actual implementation. In particular, this applies to many business applications which are run on a mainframe computer and are written in COBOL. Many companies are confronted with the difficult task of migrating these systems to a client/server architecture with clients running on PCs and servers running on the mainframe. REforDI (REengineering for DIstribution) is a graph-based environment supporting this task. REforDI provides integrated code analysis, re-design, and code transformation for COBOL applications. To prepare the application for distribution, REforDI assists in the transition to an object-based architecture, according to which the source code is subsequently transformed into Object COBOL. Internally, REforDI makes heavy use of generators to reduce the implementation effort and thus to enhance adaptability. In particular, graph-based tools for re-engineering are generated from a formal specification which is based on programmed graph transformations. Copyright © 2002 John Wiley & Sons, Ltd. [source] Abscheidung von Palladium und Palladiumlegierungen mit hohen Schichtdicken für die MikrosystemtechnikMATERIALWISSENSCHAFT UND WERKSTOFFTECHNIK, Issue 2 2007E. Günther Palladium and palladium alloys; Heavy deposits are used; Microsystems technology; Internal stress; Graph of current density vs. potential Abstract Die Abscheidung von Metallen und Legierungen in Mikrostrukturen erfordert meist eine Schichtdicke größer als 100 ,m, die der Strukturhöhe entspricht. Für die Nutzung von Edelmetallen in Mikrosystemen ist die Abscheidung von spannungsarmen, rissfreien, porenfreien und duktilen Schichten notwendig. Da die kommerziell abgeschiedenen Edelmetallschichten nur bis etwa 10 ,m qualitätsgerecht abgeschieden werden können, sind geeignete Zusätze und Variation der Abscheidungsbedingungen erforderlich, um mikrosystemtaugliche Elektrolyte zu entwickeln. Charakterisierung der Schichteigenschaften, Parameter der Abscheidungstechnologie und Anwendungsbeispiele werden aufgeführt. Erste Ergebnisse werden vorgestellt und diskutiert. Deposition of Thick Palladium and Palladium Alloy Layers for Microsystems Technology Layers of metals and alloys deposited in microstructures usually require to be thicker than the 100 ,m which is the approximate height of the structure. The deposited form of noble metals used in microsystems must be non-stressed, ductile and free of cracks and pores. As the thickness of layers deposited from commercial noble metal electrolytes will rarely exceed 10 ,m without loss of quality, developing an electrolyte system suitable for microsystems involves finding appropriate additives and deposition parameters. Details are given of deposit characterisation, the parameters of the deposition technology and some practical examples. Initial results are presented and discussed. [source] Ionothermal Synthesis of Extra-Large-Pore Open-Framework Nickel Phosphite 5,H3O,[Ni8(HPO3)9Cl3],1.5,H2O: Magnetic Anisotropy of the Antiferromagnetism,ANGEWANDTE CHEMIE, Issue 13 2010Hongzhu Xing Mikroporöse Magnete: Die Struktur der Titelverbindung (siehe Einschub) weist zweidimensionale Nickel-Sauerstoff/Chlorid-18-Ring-Schichten auf, die entlang der c -Achse gestapelt und durch HPO3 -Einheiten verknüpft sind. Nach Messungen der magnetischen Anisotropie an ausgerichteten Einkristallen (siehe Graph) ist die leichte magnetische Achse senkrecht zur Schichtebene. [source] Ein Kalium-modifiziertes Mg(NH2)2/2,LiH-System für die Wasserstoffspeicherung,ANGEWANDTE CHEMIE, Issue 32 2009Jianhui Wang Die Wasserstoffdesorption wird durch Zugabe von KH zu Mg(NH2)2/LiH drastisch beschleunigt. Die Abgabe von Wasserstoff aus dem Kalium-modifizierten System setzt bei ca. 80,°C ein (siehe Graph). Etwa 5,Gew.-% Wasserstoff können bei ca. 107,°C umkehrbar de- und absorbiert werden. Die Gegenwart von Kalium im reagierenden System schwächt die Amid-N-H- und die Imid-Li-N-Bindungen und führt so zu einer verbesserten Reaktionskinetik. [source] The Readability of Path-Preserving Clusterings of GraphsCOMPUTER GRAPHICS FORUM, Issue 3 2010Daniel Archambault Abstract Graph visualization systems often exploit opaque metanodes to reduce visual clutter and improve the readability of large graphs. This filtering can be done in a path-preserving way based on attribute values associated with the nodes of the graph. Despite extensive use of these representations, as far as we know, no formal experimentation exists to evaluate if they improve the readability of graphs. In this paper, we present the results of a user study that formally evaluates how such representations affect the readability of graphs. We also explore the effect of graph size and connectivity in terms of this primary research question. Overall, for our tasks, we did not find a significant difference when this clustering is used. However, if the graph is highly connected, these clusterings can improve performance. Also, if the graph is large enough and can be simplified into a few metanodes, benefits in performance on global tasks are realized. Under these same conditions, however, performance of local attribute tasks may be reduced. [source] Motorcycle Graphs: Canonical Quad Mesh PartitioningCOMPUTER GRAPHICS FORUM, Issue 5 2008David Eppstein Abstract We describe algorithms for canonically partitioning semi-regular quadrilateral meshes into structured submeshes, using an adaptation of the geometric motorcycle graph of Eppstein and Erickson to quad meshes. Our partitions may be used to efficiently find isomorphisms between quad meshes. In addition, they may be used as a highly compressed representation of the original mesh. These partitions can be constructed in sublinear time from a list of the extraordinary vertices in a mesh. We also study the problem of further reducing the number of submeshes in our partitions,we prove that optimizing this number is NP-hard, but it can be efficiently approximated. [source] Centrality Based Visualization of Small World GraphsCOMPUTER GRAPHICS FORUM, Issue 3 2008F. Van Ham Abstract Current graph drawing algorithms enable the creation of two dimensional node-link diagrams of huge graphs. However, for graphs with low diameter (of which "small world" graphs are a subset) these techniques begin to break down visually even when the graph has only a few hundred nodes. Typical algorithms produce images where nodes clump together in the center of the screen, making it hard to discern structure and follow paths. This paper describes a solution to this problem, which uses a global edge metric to determine a subset of edges that capture the graph's intrinsic clustering structure. This structure is then used to create an embedding of the graph, after which the remaining edges are added back in. We demonstrate applications of this technique to a number of real world examples. [source] Changing Graph Use in Corporate Annual Reports: A Time-Series AnalysisCONTEMPORARY ACCOUNTING RESEARCH, Issue 2 2000VIVIEN A. BEATTIE Abstract Graphs in corporate annual reports form part of a powerfully designed annual report package that offers considerable potential for "impression management." The primary purpose of this paper is to determine whether graph use depends on corporate performance. Time-series analysis, not previously used in the financial graphs literature, allows discretionary changes in graph use by companies to be identified and related to changes in individual companies' corporate performance over time. Based on the prior financial graphs and accounting choice literature, we develop two hypotheses that relate changes in graph use to changes in corporate performance. These hypotheses focus on the aggregate and individual company levels. We base our analysis on the corporate annual reports of 137 top UK companies that were in continued existence during the five-year period from 1988 to 1992. At both the aggregate and individual company levels, we find the decision to use key financial variable (KFV) graphs, the primary graphical choice, to be associated positively with corporate performance measures. This finding is consistent with the manipulation hypothesis - that is, that financial graphs in corporate annual reports are used to "manage" favorably the reader's impression of company performance, and hence that there is a reporting bias. [source] Estimating Background and Threshold Nitrate Concentrations Using Probability GraphsGROUND WATER, Issue 5 2006S.V. Panno Because of the ubiquitous nature of anthropogenic nitrate () in many parts of the world, determining background concentrations of in shallow ground water from natural sources is probably impossible in most environments. Present-day background must now include diffuse sources of such as disruption of soils and oxidation of organic matter, and atmospheric inputs from products of combustion and evaporation of ammonia from fertilizer and livestock waste. Anomalies can be defined as derived from nitrogen (N) inputs to the environment from anthropogenic activities, including synthetic fertilizers, livestock waste, and septic effluent. Cumulative probability graphs were used to identify threshold concentrations separating background and anomalous NO3 -N concentrations and to assist in the determination of sources of N contamination for 232 spring water samples and 200 well water samples from karst aquifers. Thresholds were 0.4, 2.5, and 6.7 mg/L for spring water samples, and 0.1, 2.1, and 17 mg/L for well water samples. The 0.4 and 0.1 mg/L values are assumed to represent thresholds for present-day precipitation. Thresholds at 2.5 and 2.1 mg/L are interpreted to represent present-day background concentrations of NO3 -N. The population of spring water samples with concentrations between 2.5 and 6.7 mg/L represents an amalgam of all sources of in the ground water basins that feed each spring; concentrations >6.7 mg/L were typically samples collected soon after springtime application of synthetic fertilizer. The 17 mg/L threshold (adjusted to 15 mg/L) for well water samples is interpreted as the level above which livestock wastes dominate the N sources. [source] Resolution errors associated with gridded precipitation fieldsINTERNATIONAL JOURNAL OF CLIMATOLOGY, Issue 15 2005C. J. Willmott Abstract Spatial-resolution errors are inherent in gridded precipitation (P) fields,such as those produced by climate models and from satellite observations,and they can be sizeable when P is averaged spatially onto a coarse grid. They can also vary dramatically over space and time. In this paper, we illustrate the importance of evaluating resolution errors associated with gridded P fields by investigating the relationships between grid resolution and resolution error for monthly P within the Amazon Basin. Spatial-resolution errors within gridded-monthly and average-monthly P fields over the Amazon Basin are evaluated for grid resolutions ranging from 0.1° to 5.0°. A resolution error occurs when P is estimated for a location of interest within a grid-cell from the unbiased, grid-cell average P. Graphs of January, July and annual resolution errors versus resolution show that, at the higher resolutions (<3° ), aggregation quickly increases resolution error. Resolution error then begins to level off as the grid becomes coarser. Within the Amazon Basin, the largest resolution errors occur during January (summer), but the largest percentage errors appear in July (winter). In January of 1980, e.g., resolution errors of 29, 52 and 65 mm,or 11, 19 and 24% of the grid-cell means,were estimated at resolutions of 1.0°, 3.0° and 5.0°. In July of 1980, however, the percentage errors at these three resolutions were considerably larger, that is, 15%, 27% and 33% of the grid-cell means. Copyright © 2005 Royal Meteorological Society [source] Growth of Self-Similar GraphsJOURNAL OF GRAPH THEORY, Issue 3 2004B. Krön Abstract Locally finite self-similar graphs with bounded geometry and without bounded geometry as well as non-locally finite self-similar graphs are characterized by the structure of their cell graphs. Geometric properties concerning the volume growth and distances in cell graphs are discussed. The length scaling factor , and the volume scaling factor , can be defined similarly to the corresponding parameters of continuous self-similar sets. There are different notions of growth dimensions of graphs. For a rather general class of self-similar graphs, it is proved that all these dimensions coincide and that they can be calculated in the same way as the Hausdorff dimension of continuous self-similar fractals: . © 2004 Wiley Periodicals, Inc. J Graph Theory 45: 224,239, 2004 [source] Price Dynamics in the International Wheat Market: Modeling with Error Correction and Directed Acyclic GraphsJOURNAL OF REGIONAL SCIENCE, Issue 1 2003David A Bessler In this paper we examine dynamic relationships among wheat prices from five countries for the years 1981,1999. Error correction models and directed acyclic graphs are employed with observational data to sort,out the dynamic causal relationships among prices from major wheat producing regions: Canada, the European Union, Argentina, Australia, and the United States. An ambiguity related to the cyclic or acyclic flow of information between Canada and Australia is uncovered. We condition our analysis on the assumption that information flow is acyclic. The empirical results show that Canada and the U.S. are leaders in the pricing of wheat in these markets. The U.S. has a significant effect on three markets excluding Canada. [source] Activation energy of thermally grown silicon dioxide layers on silicon substratesPHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 10 2009G. Gerlach Abstract A detailed numerical consideration is used as basic approach for calculating profiles of activation energy versus oxide thickness for various temperatures between 780 and 930,°C. Results presented here are intentionally not based on models of diffusion and reaction kinetics to avoid introducing correction terms due to the expansion of theory still under discussion. The statistical calculation gives the mean activation energy of 2.01,eV with standard deviation of 0.10,eV, very close to the overall activation energy of 2.05,eV [M. A. Rabie, Y. M. Haddara, and J. Carette, J. Appl. Phys. 98, 074904 (2005)]. More instructive features of the thermal oxidation of silicon have been disclosed directly from measurements of oxide thickness with time [M. A. Hopper, R. A. Clarke, and L. Young, J. Electrochem. Soc. 122, 1216 (1975) and J. Blanc, Philos. Mag. B 55, 685 (1987)]. Graphs of the natural logarithm of the growth rate versus oxide thickness, in the range between 2 and 65,nm, show that the oxide thickness influences the activation energy EA between 1.4 and 2.7,eV. [source] Distributions of error correction tests for cointegrationTHE ECONOMETRICS JOURNAL, Issue 2 2002Neil R. Ericsson Summary This paper provides densities and finite sample critical values for the single-equation error correction statistic for testing cointegration. Graphs and response surfaces summarize extensive Monte Carlo simulations and highlight simple dependencies of the statistic's quantiles on the number of variables in the error correction model, the choice of deterministic components, and the sample size. The response surfaces provide a convenient way for calculating finite sample critical values at standard levels; and a computer program, freely available over the Internet, can be used to calculate both critical values and p -values. Two empirical applications illustrate these tools. [source] Diffusion and NOE NMR Studies on Multicationic DAB-Organoruthenium Dendrimers: Size-Dependent Noncovalent Self-Assembly to Megamers and Ion Pairing,CHEMISTRY - A EUROPEAN JOURNAL, Issue 21 2009Stefania Pettirossi Dr. Abstract Supra-mega ion pairing: Multicationic organoruthenium dendrimers show a notable tendency to self-aggregate when the concentration is increased, leading to megamers. This tendency increases with the generation. The self-aggregation of dendrimers to megamers is coupled with a decrease in the extent of ion pairing, as illustrated. New multicationic organoruthenium dendrimers (RuPF6 -Dabn, n=2, 4, 8, 16) have been synthesized by coupling of [Ru(,6 - p -cymene)(,3 -dpk-OCH2CH2OH)]X (1PF6, dpk=2,2,-dipyridyl ketone, X=PF6) with 1,4-diaminobutane (DAB) and polypropylenimine dendrimer DAB- dendr -(NH2)n {n=4, 8, 16} mediated by 1,1,-carbonyldiimidazole (CDI). The intermediate in the synthesis, [Ru(,6 - p -cymene)(,3 -dpk-OCH2CH2OC(O)Im]X (2PF6, Im=imidazole, X=PF6) has been isolated and characterized by single-crystal XRD. The intra- and supramolecular structures in a solution of RuPF6 -Dabn dendrimer have been investigated by multidimensional and multinuclear NMR techniques. Diffusion NMR experiments on dilute solutions indicated that the linear distance between two metal centers (14.9,22.1,Å depending on the dendrimer generation) is much greater than the diameter of 1PF6 (9.9,Å). 19F,1H-HOESY NMR experiments (HOESY= heteronuclear Overhauser effect spectroscopy) showed that the counterion is positioned on the surface of the dendrimers and assumes the same relative anion,cation orientation as in 2PF6. Diffusion NMR experiments on RuPF6 -Dabn dendrimers in CD2Cl2 at different concentrations revealed a process of supramolecular assembly of dendrimers to megamers that is strongly favored for the highest generations. Megamer formation is coupled with an increased fraction of free ions (,) and a consequent reduction in ion-paired ruthenium centers. Graphs of , versus CRu (the concentration of ruthenium centers) showed a minimum for RuPF6 -Dab4, RuPF6 -Dab8, and RuPF6 -Dab16 at a position coinciding with the significant presence of supramolecular dendritic dimers. The tendency to ion pairing decreases as the dendrimer generation increases. [source] PREPROCESSING RULES FOR TRIANGULATION OF PROBABILISTIC NETWORKS,COMPUTATIONAL INTELLIGENCE, Issue 3 2005Hans L. Bodlaender Currently, the most efficient algorithm for inference with a probabilistic network builds upon a triangulation of a network's graph. In this paper, we show that pre-processing can help in finding good triangulations for probabilistic networks, that is, triangulations with a maximum clique size as small as possible. We provide a set of rules for stepwise reducing a graph, without losing optimality. This reduction allows us to solve the triangulation problem on a smaller graph. From the smaller graph's triangulation, a triangulation of the original graph is obtained by reversing the reduction steps. Our experimental results show that the graphs of some well-known real-life probabilistic networks can be triangulated optimally just by preprocessing; for other networks, huge reductions in their graph's size are obtained. [source] New Concepts in Evolutionary Search for Boolean Functions in CryptologyCOMPUTATIONAL INTELLIGENCE, Issue 3 2004William Millan In symmetric cryptology the resistance to attacks depends critically on the nonlinearity properties of the Boolean functions describing cipher components like Substitution boxes (S-boxes). Some of the most effective methods known to generate functions that satisfy multiple criteria are based on evolutionary heuristics. In this paper, we improve on these algorithms by employing an adaptive strategy. Additionally, using recent improvements in the understanding of these combinatorial structures, we discover essential properties of the graph formed by affine equivalence classes of Boolean functions, which offers several advantages as a conceptual model for multiobjective seeking evolutionary heuristics. Finally, we propose the first major global cooperative effort to discover new bounds for cryptographic properties of Boolean functions. [source] Myriad: scalable VR via peer-to-peer connectivity, PC clustering, and transient inconsistencyCOMPUTER ANIMATION AND VIRTUAL WORLDS (PREV: JNL OF VISUALISATION & COMPUTER ANIMATION), Issue 1 2007Benjamin Schaeffer Abstract Distributed scene graphs are important in virtual reality, both in collaborative virtual environments and in cluster rendering. Modern scalable visualization systems have high local throughput, but collaborative virtual environments (VEs) over a wide-area network (WAN) share data at much lower rates. This complicates the use of one scene graph across the whole application. Myriad is an extension of the Syzygy VR toolkit in which individual scene graphs form a peer-to-peer network. Myriad connections filter scene graph updates and create flexible relationships between nodes of the scene graph. Myriad's sharing is fine-grained: the properties of individual scene graph nodes to share are dynamically specified (in C++ or Python). Myriad permits transient inconsistency, relaxing resource requirements in collaborative VEs. A test application, WorldWideCrowd, demonstrates collaborative prototyping of a 300-avatar crowd animation viewed on two PC-cluster displays and edited on low-powered laptops, desktops, and over a WAN. We have further used our framework to facilitate collaborative educational experiences and as a vehicle for undergraduates to experiment with shared virtual worlds. Copyright © 2006 John Wiley & Sons, Ltd. [source] On-line motion blending for real-time locomotion generationCOMPUTER ANIMATION AND VIRTUAL WORLDS (PREV: JNL OF VISUALISATION & COMPUTER ANIMATION), Issue 3-4 2004Sang Il Park Abstract In this paper, we present an integrated framework of on-line motion blending for locomotion generation. We first provide a novel scheme for incremental timewarping, which always guarantees that the time goes forward. Combining the idea of motion blending with that of posture rearrangement, we introduce a motion transition graph to address on-line motion blending and transition simultaneously. Guided by a stream of motion specifications, our motion synthesis scheme moves from node to node in an on-line manner while blending a motion at a node and generating a transition motion at an edge. For smooth on-line motion transition, we also attach a set of example transition motions to an edge. To represent similar postures consistently, we exploit the inter-frame coherency embedded in the input motion specification. Finally, we provide a comprehensive solution to on-line motion retargeting by integrating existing techniques. Copyright © 2004 John Wiley & Sons, Ltd. [source] Winding Roads: Routing edges into bundlesCOMPUTER GRAPHICS FORUM, Issue 3 2010A. Lambert Abstract Visualizing graphs containing many nodes and edges efficiently is quite challenging. Drawings of such graphs generally suffer from visual clutter induced by the large amount of edges and their crossings. Consequently it is difficult to read the relationships between nodes and the high-level edge patterns that may exist in standard node-link diagram representations. Edge bundling techniques have been proposed to help solve this issue, which rely on high quality edge rerouting. In this paper, we introduce an intuitive edge bundling technique which efficiently reduces edge clutter in graphs drawings. Our method is based on the use of a grid built using the original graph to compute the edge rerouting. In comparison with previously proposed edge bundling methods, our technique improves both the level of clutter reduction and the computation performance. The second contribution of this paper is a GPU-based rendering method which helps users perceive bundles densities while preserving edge color. [source] The Readability of Path-Preserving Clusterings of GraphsCOMPUTER GRAPHICS FORUM, Issue 3 2010Daniel Archambault Abstract Graph visualization systems often exploit opaque metanodes to reduce visual clutter and improve the readability of large graphs. This filtering can be done in a path-preserving way based on attribute values associated with the nodes of the graph. Despite extensive use of these representations, as far as we know, no formal experimentation exists to evaluate if they improve the readability of graphs. In this paper, we present the results of a user study that formally evaluates how such representations affect the readability of graphs. We also explore the effect of graph size and connectivity in terms of this primary research question. Overall, for our tasks, we did not find a significant difference when this clustering is used. However, if the graph is highly connected, these clusterings can improve performance. Also, if the graph is large enough and can be simplified into a few metanodes, benefits in performance on global tasks are realized. Under these same conditions, however, performance of local attribute tasks may be reduced. [source] Scalable, Versatile and Simple Constrained Graph LayoutCOMPUTER GRAPHICS FORUM, Issue 3 2009Tim Dwyer Abstract We describe a new technique for graph layout subject to constraints. Compared to previous techniques the proposed method is much faster and scalable to much larger graphs. For a graph with n nodes, m edges and c constraints it computes incremental layout in time O(n log n+m+c) per iteration. Also, it supports a much more powerful class of constraint: inequalities or equalities over the Euclidean distance between nodes. We demonstrate the power of this technique by application to a number of diagramming conventions which previous constrained graph layout methods could not support. Further, the constraint-satisfaction method,inspired by recent work in position-based dynamics,is far simpler to implement than previous methods. [source] | ||||||||||||||||||||||||||||