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Item Open Access Iterative algorithms for solution of large sparse systems of linear equations on hypercubes(IEEE, 1988) Aykanat, Cevdet; Özgüner, F.; Ercal, F.; Sadayappan, P.Show more Finite-element discretization produces linear equations in the form Ax=b, where A is large, sparse, and banded with proper ordering of the variables x. The solution of such equations on distributed-memory message-passing multiprocessors implementing the hypercube topology is addressed. Iterative algorithms based on the conjugate gradient method are developed for hypercubes designed for coarse-grained parallelism. The communication requirements of different schemes for mapping finite-element meshes onto the processors of a hypercube are analyzed with respect to the effect of communication parameters of the architecture. Experimental results for a 16-node Intel 80386-based iPSC/2 hypercube are presented and discussed.Show more Item Open Access Continuous processing of images through user sketched functional blocks(Wiley-Blackwell, 1988) Kaya, A.; Ozguc, B.Show more Our aim is to implement an image processing system with previously defined algorithms through the use of functional blocks connected together to form a diagram that we call a schematic. A functional block means the representation of a routine or function by a visual object in our intent. The arc connecting two blocks is the path and direction through which an image is transferred. In the development of the system we relied on the usage of new developments in software providing for the construction of better interfaces. Most important of these are the object oriented style of programming, iconic interfacing, multiple window and multi-tasking operating systems.Show more Item Open Access A simple animation package(Pergamon Press, 1988) Coşar, A.; Özgüç, B.Show more This paper discusses a simple animation package that animates sketches drawn by the user through a simple set of operations. The purpose of the animation package is to demonstrate various computer graphics principles to those who are not experienced in the subject. Furthermore, it is an education tool for both art and undergraduate students. An expanded set of utilities allows for journaling for playback as well as a single level undo. This provides for an easy modification or correction of the errors that can be made during any session. The system is written in C language on a Unix workstation environment. User input is handled through a menu driven system and the benefits of an event driven window environment are fully made use of [6]. This obviously simplifies the usage of the package by the merits of such an environment.Show more Item Open Access Dynamic congestion control in interconnected computer networks(IEEE, 1988-10) Ulusoy, Özgür; Baray, MehmetShow more The authors evaluate a window-based congestion control mechanism in an internetwork environment. They also propose and study two dynamic-window congestion-control algorithms. These algorithms provide further control to the window mechanism by adjusting the window size in accordance with the availability of the network resources at the destination. A comparison of dynamic algorithms with fixed window control is provided in terms of throughput and delay performance. It is shown that dynamic algorithms have considerable performance advantages over fixed-window control.Show more Item Open Access The power of physical representations(AAAI Press, 1989) Akman, V.; ten Hagen, P. J. W.Show more Commonsense reasoning about the physical world, as exemplified by 'Iron sinks in water' or 'If a ball is dropped it gains speed,' will be indispensable in future programs. We argue that to make such predictions (namely, envisioning), programs should use abstract entities (such as the gravitational field), principles (such as the principle of superposition), and laws (such as the conservation of energy) of physics for representation and reasoning. These arguments are in accord with a recent study in physics instruction where expert problem solving is related to the construction of physical representations that contain fictitious, imagined entities such as forces and momenta. We give several examples showing the power of physical representations.Show more Item Open Access Design and implementation of a tool for teaching programming(1989) Göktepe, Mesut; Özgüç, Bülent; Baray, MehmetShow more Recently, computers have been widely used in almost all fields of education. Our approach to computer aided education is mainly concerned with programming. Here, it is intended to teach the Pascal language for problem solving in a visual manner. In this project, we have used an object oriented approach for the implementation of an educational tool for programming. The paper mainly discusses the topics related to computer aided education, user interface, object oriented programming and ongoing research related to the project.Show more Item Open Access Geometric computing and uniform grid technique(Elsevier, 1989) Akman, W.; Franklin, W. R.; Kankanhalli, M.; Narayanaswami, C.Show more If computational geometry should play an important role in the professional environment (e.g. graphics and robotics), the data structures it advocates should be readily implemented and the algorithms efficient. In the paper, the uniform grid and a diverse set of geometric algorithms that are all based on it, are reviewed. The technique, invented by the second author, is a flat, and thus non-hierarchical, grid whose resolution adapts to the data. It is especially suitable for telling efficiently which pairs of a large number of short edges intersect. Several of the algorithms presented here exist as working programs (among which is a visible surface program for polyhedra) and can handle large data sets (i.e. many thousands of geometric objects). Furthermore, the uniform grid is appropriate for parallel processing; the parallel implementation presented gives very good speed-up results. © 1989.Show more Item Open Access Ray representation for k-trees(Elsevier, 1989) Akman, V.; Franklin, Wm. R.Show more k-trees have established themselves as useful data structures in pattern recognition. A fundamental operation regarding k-trees is the construction of a k-tree. We present a method to store an object as a set of rays and an algorithm to convert such a set into a k-tree. The algorithm is conceptually simple, works for any k, and builds a k-tree from the rays very fast. It produces a minimal k-tree and does not lead to intermediate storage swell. © 1989.Show more Item Open Access Representing objects as rays, or how to pile up an octree?(Elsevier, 1989) Akman, V.; Franklin, Wm. R.Show more Quadtrees, octrees, and in general k-trees have established themselves as useful hierarchical data structures in computer graphics, image processing, and solid modeling. A fundamental operation in a system based on k-trees is the construction of a k-tree. Here, we review a new way of doing this operation. Basically, we have invented a method to store an object as a set of rays and an algorithm for converting such a set into a k-tree. (For example, in 3D a ray is a thin parallelepiped.) The algorithm is conceptually simple, works for any k, and piles up, using an approach we call stacking, a k-tree from the rays very fast. It produces a minimal k-tree and does not lead to intermediate storage swell. For large-scale realistic objects, which consist of many thousands of rays, the algorithm debunks the "expensive octree creation" myth. © 1989.Show more Item Open Access Time-by-example query language for historical databases(IEEE, 1989) Tansel, A. U.; Arkun, M. E.; Ozsoyoglu, G.Show more Time-by-Example (TBE) is a user-friendly query language designed specifically for historical relational databases. It follows the graphical structure and the example query concept of QBE, and employs the hierarchical arrangement of subqueries of Abe and STBE. Similar to STBE, TBE handles set- and simple-valued attributes. In addition, to handle time, TBE is capable of manipulating triplet- and set-triplet-valued attributes. The underlying data model used in TBE is an extended relational data model in which nonfirst normal form relations and attribute time stamping (in contrast to tuple time stamping) are used. A triplet is a 3-tuple whose components are the lower and upper bounds of a time interval and a value valid over the interval. A triplet is used as a timestamped value of a time-dependent attribute. Set-valued time-dependent attributes are modeled by sets of triplets. To process TBE queries and to define a historical relational algebra (HRA), standard operators of the relational algebra and the packlunpack operators of [Zl] are augmented by triplet-decomposition, tripletformation, slice, and drop-time operators. Methodologies for translating TBE queries into HRA expressions and for constructing their parse trees are presented.Show more Item Open Access Task allocation onto a hypercube by recursive mincut bipartitioning(Elsevier, 1990) Ercal, F.; Ramanujam, J.; Sadayappan, P.Show more An efficient recursive task allocation scheme, based on the Kernighan-Lin mincut bisection heuristic, is proposed for the effective mapping of tasks of a parallel program onto a hypercube parallel computer. It is evaluated by comparison with an adaptive, scaled simulated annealing method. The recursive allocation scheme is shown to be effective on a number of large test task graphs-its solution quality is nearly as good as that produced by simulated annealing, and its computation time is several orders of magnitude lessShow more Item Open Access Vectorization and parallelization of the conjugate gradient algorithm on hypercube-connected vector processors(Elsevier, 1990) Aykanat, Cevdet; Özgüner, F.; Scott, D. S.Show more Solution of large sparse linear systems of equations in the form constitutes a significant amount of the computations in the simulation of physical phenomena [1]. For example, the finite element discretization of a regular domain, with proper ordering of the variables x, renders a banded N × N coefficient matrix A. The Conjugate Gradient (CG) [2,3] algorithm is an iterative method for solving sparse matrix equations and is widely used because of its convergence properties. In this paper an implementation of the Conjugate Gradient algorithm, that exploits both vectorization and parallelization on a 2-dimensional hypercube with vector processors at each node (iPSC-VX/d2), is described. The implementation described here achieves efficient parallelization by using a version of the CG algorithm suitable for coarse grain parallelism [4,5] to reduce the communication steps required and by overlapping the computations on the vector processor with internode communication. With parallelization and vectorization, a speedup of 58 over a μVax II is obtained for large problems, on a two dimensional vector hypercube (iPSC-VX/d2).Show more Item Open Access Free-form solid modeling using deformations(Pergamon Press, 1990) Güdükbay, Uğur; Özgüç, B.Show more One of the most important problems of available solid modeling systems is that the range of shapes generated is limited. It is not easy to model objects with free-form surfaces in a conventional solid modeling system. Such objects can be defined arbitrarily, but then operations on them are not transparent and complications occur. A method for achieving free-form effect is to define regular objects or surfaces, then deform them. This keeps various properties of the model intact while achieving the required visual appearance. This paper discusses a number of geometric modeling techniques with deformations applied to them in attempts to combine various approaches developed so far.Show more Item Open Access A fundamental and theoretical framework for an intelligent CAD system(Pergamon Press, 1990) Akman, V.; Hagen, P. J. W. T.; Tomiyama, T.Show more Currently, there exists a line of research in mechanical CAD that is directed towards using AI and knowledge engineering ideas, but truly unifying approaches in this respect are lacking. The authors hope to fill this gap via a logic-based, theoretical approach. A formulation is given for how a designer's apprentice (or a design workbench) can be established. The relevance of naive physics and commonsense reasoning in machine design are demonstrated. As for the software development methodology several aspects of software engineering are considered. A design base language which is built upon logic programming and object-oriented programming paradigm is proposed. © 1990.Show more Item Open Access Architectural sketch recognition(1990) Durgun, Fatoş Bengi; Özgüç, BülentShow more Sketch recognition is applied to freehand architectural drawings. The purpose is to recognize the architect’s intentions from a quick sketch and generate a detailed drawing. The system can also calibrate itself to interpret the peculiar styles of each individual architect using it. © 1990 Taylor and Francis Group, LLC.Show more Item Open Access Learning problem solving strategies using refinement and macro generation(Elsevier BV, 1990) Güvenir, H. A.; Ernst, G. W.Show more In this paper we propose a technique for learning efficient strategies for solving a certain class of problems. The method, RWM, makes use of two separate methods, namely, refinement and macro generation. The former is a method for partitioning a given problem into a sequence of easier subproblems. The latter is for efficiently learning composite moves which are useful in solving the problem. These methods and a system that incorporates them are described in detail. The kind of strategies learned by RWM are based on the GPS problem solving method. Examples of strategies learned for different types of problems are given. RWM has learned good strategies for some problems which are difficult by human standards. © 1990.Show more Item Open Access An extended user interface for CAL systems(1990) Davenport, DavidShow more This paper examines the problems of complexity in human-computer interaction from the perspective of CAL systems. By considering the very special demands of young, pre-reading age children, it shows how pointing type interfaces can be extended in a simple and natural manner based on the notion that the position of, and spatial relationship between objects, is of significance. Various examples based on this extended interface concept are introduced to demonstrate its functionality.Show more Item Open Access The role of location of traffic control in internetwork gateways(IEEE, 1990-03) Ulusoy, Özgür; Baray, MehmetShow more Summary form only given. An evaluation of window-based gateway-to-gateway-level congestion control in an interconnected network environment is reported. Two dynamic control algorithms proposed by the author are intended to operate the system below the critical internetwork load that gives rise to congestion at gateways and connected networks. In one of the algorithms, source gateways regulate the traffic flow, whereas in the other, destination gateways provide the control. The algorithms provide further control to static window protocol by adjusting the window size in accordance with the availability of network resources at the destination. A comparison of the two algorithms has shown that controlling the internetwork messages at the destination gateway produces better performance results than control at the source gateway.Show more Item Open Access Unification-based approach for knowledge base verification(1991) Polat, F.; Guvenir, H. A.Show more Knowledge base verification, a part of the validation process in expert system development, includes checking the knowledge base for completeness and consistency to guard against a variety of errors that can arise during the process of transferring expertise from a human expert to a computer system. Regardless of how an expert system is developed, its developers can profit from a systematic check of the knowledge base without gathering extensive data for test runs, even before the full reasoning mechanism is functioning. Until recently knowledge base verification has been largely ignored, which has led to expert systems with knowledge base errors and no safety factors for correctness. We propose a unification-based approach for verification of a knowledge base represented in the form of production rules and facts. This approach can determine conflicting, redundant, subsumed and circular rules; redundant if-conditions in rules; dead-end rules; and cycles and contradiction in rules.Show more Item Open Access Fast ray tracing 3D models(1991) İşler, Veysi; Özgüç, BülentShow more In many computer graphics applications such as CAD, realistic displays have very important and positive effects on the users of the system. There are several techniques to generate realistic images with the computer. Ray tracing gives the most effective results by simulating the interaction of light with its environment. However, it may require an excessive amount of time to generate an image. In this article, we present a survey of methods developed to speed up the ray tracing algorithm and introduce a fast ray tracer to process a 3D scene that is defined by interactive 3D modeling software.Show more