We study the problem of automatic frequency assignment for cellular telephone systems. The frequency assignment problem is viewed as the problem to minimize the unsatisfied soft constraints in a constraint satisfaction problem (CSP) over a finite domain of frequencies involving co-channel, adjacent channel, and co-site constraints. The soft constraints are automatically derived from signal strength prediction data. The CSP is solved using a generalized graph coloring algorithm. Graph-theoretical results play a crucial role in making the problem tractable. Performance results from a real-world frequency assignment problem are presented. We develop the generalized graph coloring algorithm by stepwise refinement, starting from DSATUR and augmenting it with local propagation, constraint lifting, intelligent backtracking, redundancy avoidance, and iterative deepening. Key Words: frequency assignment, constraints, graph coloring, intelligent backtracking, iterative deepening. 1 Introduction...

Data mining is the nontrivial extraction of implicit, previously unknown, and potentially useful information from data. As one of the most important background knowledge, concept hierarchy plays a fundamentally important role in data mining. It is the purpose of this thesis to study some aspects of concept hierarchy such as the automatic generation and encoding technique in the context of data mining. After the discussion on the basic terminology and categorization, automatic generation of concept hierarchies is studied for both nominal and numerical hierarchies. One algorithm is designed for determining the partial order on a given set of nominal attributes. The resulting partial order is a useful guide for users to finalize the concept hierarchy for their particular data mining tasks. Based on hierarchical and partitioning clustering methods, two algorithms are proposed for the automatic generation of numerical hierarchies. The quality and performance comparisons indicates that the ...

An important recent idea to facilitate knowledge sharing is to provide libraries of reusable components (models, ontologies) to end users. However, when libraries become large, finding the right library components is a knowledge demanding task in itself. Our suggestion therefore is that methods will be needed that help the user to gradually construct such knowledge.

This dissertation proposes a new epidemiological model to account for particular characteristics of computer worm epidemics. This new model, termed the Progressive Susceptible-Infected-Detected-Removed (PSIDR) epidemiological model, incorporates new aspects related to the availability of antivirus signatures, to the existence of direct immunization, and to the presence of a curing phase. Various costs are incorporated in the model, which allow us to determine the best strategies to fight worms. The model undergoes an extensive series of validation tests, its properties being evaluated mostly numerically. The model shows good agreement with empirical data. The paper then investigates current response strategies as well as the effect of virus throttling. The model yields both practical recommendations and new insights about the observed low prevalence of worms over the Internet

During the last two decades, many heuristic procedures for the joint replenishment problem have appeared in the literature. The only available optimal solution procedure was based on an enumerative approach and was computationally prohibitive. In this paper we present an alternative optimal approach based on global optimisation theory. By applying Lipschitz optimisation one can find a solution with an arbitrarily small deviation from an optimal value. An efficient procedure is presented which uses a dynamic Lipschitz constant and generates a solution in little time. The running time of this procedure grows only linearly in the number of items. Keywords: Inventory, joint replenishment, multi-item, global optimisation, Lipschitz optimisation 1 Introduction In an inventory system with multiple items, cost savings can be obtained when the replenishment of several items are coordinated. Each time an order is placed, a major ordering cost is incurred, independent of the number of items ord...

In this paper, we develop a queueing model for wormhole routing with finite size buffers. This model assumes the use of a deadlock-free routing scheme that guarantees no cycle of link dependency (defined in section 3). Several approximation methods for estimating the output link contention delay and buffer queueing delay are proposed. Comparing the analytical results to simulation, we show that the model is pessimistic with regard to network performance and that the difference in network throughput is less than 10 percent. 1 Introduction Wormhole routing is a simple, low-cost switching scheme often used for supercomputer interconnections. It has the merits of low latency, low cost, and simple implementation. In addition to its use for supercomputer interconnection, wormhole routing also has been applied to high-speed local area networks (LANs) [1, 2, 3] to support applications such as cluster computing that demand a very fast, high-data-rate communication media. 1.1 Wormhole Routing...

Abstract. Clustering is a widely used approach to ease implementation of various problems such as routing and resource management in mobile ad hoc networks (MANET)s. We propose a new fully distributed algorithm for clustering in MANETs that merges clusters to form higher level clusters by increasing their levels. We show the operation of the algorithm and analyze its time and message complexities and provide results in the simulation environment of ns2. Our results conform that the algorithm proposed is scalable and has a lower time and message complexities than the other algorithms. 1

The task of computer-based free-form shape design is fraught with practical and conceptual difficulties. Incorporating elements of traditional clay sculpting has long been recognised as a means of shielding a user from the complexities inherent in this form of modelling. The premise is to deform a mathematically-defined solid in a fashion that loosely simulates the physical moulding of an inelastic substance, such as modelling clay or silicone putty. Virtual sculpting combines this emulation of clay sculpting with interactive feedback. Spatial deformations are a class of powerful modelling techniques well suited to virtual sculpting. They indirectly reshape an object by warping the surrounding space. This is analogous to embedding a flexible shape within a lump of jelly and then causing distortions by flexing the jelly. The user controls spatial deformations by manipulating points, curves or a volumetric hyperpatch. Directly Manipulated Free-Form Deformation (DMFFD), in particular, me...

In this paper, we propose a scheme to identify the maximal fault-free substarring. This is the first result to derive a reconfiguration scheme with high processor utilization in the faulty n-star graph. The maximal fault-free substar-ring is connected by a ring of fault-free virtual substars with dilation 3 and maximal length of the ring is n(n \Gamma 1)(n \Gamma 2). Our proposed scheme can tolerate n \Gamma 3 faults such that the processor utilization is n 2 \Gamma2n+3 n 2 \Gamman . This is a near optimal result since the maximal fault-free substar-ring is constructed by using all of the possible fault-free (n \Gamma 2)-substars. Moreover, our algorithm can still work when number of faults exceeds n \Gamma 3. The simulation results also show that the processor utilization is more than 50% if the number of faults is less than n 2 \Gamman\Gamma1 2 in the n-star graph. Keywords: Fault tolerance, interconnection network, parallel processing, reconfiguration, star graph. 1. Intr...

When designing model-based fault-diagnostic systems, the use of consistency relations (also called e.g. parity relations) is a common choice. Different consistency relations are sensitive to different subsets of faults, and thereby isolation can be achieved. This report presents an algorithm for finding a small set of submodels that can be used to derive consistency relations with highest possible diagnosis capability. The algorithm handles differential-algebraic models and is based on graph theoretical reasoning about the structure of the model. An important step towards finding these submodels, and therefore also towards finding consistency relations, is to find all minimal structurally singular (MSS) sets of equations. These sets characterize the fault diagnosability. The algorithm is applied to a large nonlinear industrial example, a part of a paper plant. In spite of the complexity of this process, a small set of consistency relations with high diagnosis capability is