High-radix switches reduce network cost and improve network performance, especially in large switch-based interconnection networks. However, there are some problems related to the integration scale to implement such s...
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High-radix switches reduce network cost and improve network performance, especially in large switch-based interconnection networks. However, there are some problems related to the integration scale to implement such switches in a single chip. An interesting alternative for building high-radix switches consists of combining several current smaller single-chip switches to obtain switches with a greater number of ports. A key design issue of this kind of high-radix switches is the internal switch configuration, specifically, the correspondence between the ports of these high-radix switches and the ports of their smaller internal single-chip switches. In this paper we use artificial intelligence and data mining techniques in order to obtain the optimal internal configuration of all the switches in the network of large supercomputers running parallel applications. Simulation results show that using the resultant switch configurations, it is possible to achieve similar performance as with single-chip switches with the same radix, which would be unfeasible with the current integration scale. (C) 2013 Elsevier Inc. All rights reserved.
searching the Web involves more than sifting through one huge graph of pages and hyperlinks. Specific association networks have emerged that serve domain-specific queries better by exploiting the principles and patter...
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searching the Web involves more than sifting through one huge graph of pages and hyperlinks. Specific association networks have emerged that serve domain-specific queries better by exploiting the principles and patterns that apply there. A technique that searches these association networks and finds nurturers-early adopters-in them can be particularly effective. Finding nurturers can improve Web search, especially when answering sticky queries-persistent searches for which a user expects frequent fresh updates. Studying the evolution of association networks offers insights that can be used for developing new forms of information retrieval and for improving searches.
Link-based information structures such as the web can be enhanced through the addition of hotlinks. Assume that each node in the information structure is associated with a weight representing the access frequency of t...
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Link-based information structures such as the web can be enhanced through the addition of hotlinks. Assume that each node in the information structure is associated with a weight representing the access frequency of the node by users. In order to access a particular node, the user must follow a path leading to it from the root. By adding new hotlinks to the tree, it may be possible to reduce the access cost of the system, namely, the expected number of steps needed to reach a leaf from the root, assuming the user can decide which hotlinks to follow in each step. The hotlink assignment problem involves finding a set of hotlinks (with at most K = O(1) hotlinks emanating from every node) maximizing the gain in the expected cost. The paper addresses this problem in two user models, namely, the traditional clairvoyant user model employed in [P. Bose, J. Czyzowicz, L. Gasieniec, E. Kranakis, D. Krizanc, A. Pelc, M.V. Martin, Strategies for hotlink assignments, in: Proc. 11th Symp. on algorithms and Computation, 2000, pp. 23-34;E. Kranakis, D. Krizanc, S. Shende, Approximating hotlink assignments, in: Proc. 12th Symp. on algorithms and Computation, 2001, pp. 756-767;P. Bose, D. Krizanc, S. Langerman, P. Morin, Asymmetrical communication protocols via hotlink assignments, in: Proc. 9th Colloq. on Structural Information and Communication Complexity, 2002, pp. 33-39;R. Matichin, D. Peleg, Approximation algorithm for hotlink assignments in web directories, in: Proc. Workshop on algorithms and Data Structures, 2003, pp. 271-280] and the more realistic greedy user model recently introduced in [O. Gerstel, S. Kutten, R. Matichin, D. Peleg, Hotlink enhancement algorithms for web directories, in: Proc. 14th Symp. on algorithms and Computation, 2003, pp. 68-77], and presents a polynomial time 2-approximation algorithm for the hotlink assignment problem on rooted directed trees. (c) 2007 Elsevier B.V. All rights reserved.
We consider several problems related to the use of resolution-based methods for determining whether a given boolean formula in conjunctive normal form is satisfiable. First, building on the work of Clegg, Edmonds, and...
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We consider several problems related to the use of resolution-based methods for determining whether a given boolean formula in conjunctive normal form is satisfiable. First, building on the work of Clegg, Edmonds, and Impagliazzo in [ Proceedings of the Twenty-Eighth Annual ACM Symposium on Theory of Computing, Philadelphia, PA, 1996, ACM, New York, 1996, pp. 174 183], we give an algorithm for unsatisfiability that when given an unsatisfiable formula of F finds a resolution proof of F. The runtime of our algorithm is subexponential in the size of the shortest resolution proof of F. Next, we investigate a class of backtrack search algorithms for producing resolution refutations of unsatisfiability, commonly known as Davis-Putnam procedures, and provide the first asymptotically tight average-case complexity analysis for their behavior on random formulas. In particular, for a simple algorithm in this class, called ordered DLL, we prove that the running time of the algorithm on a randomly generated k-CNF formula with n variables and m clauses is 2(Theta(n(n/m)1/(k-2))) with probability 1 - o(1). Finally, we give new lower bounds on res( F), the size of the smallest resolution refutation of F, for a class of formulas representing the pigeonhole principle and for randomly generated formulas. For random formulas, Chvatal and Szemeredi [J. ACM, 35 ( 1988), pp. 759 768] had shown that random 3-CNF formulas with a linear number of clauses require exponential size resolution proofs, and Fu [ On the Complexity of Proof Systems, Ph. D. thesis, University of Toronto, Toronto, ON, Canada, 1995] extended their results to k-CNF formulas. These proofs apply only when the number of clauses is Omega(n log n). We show that a lower bound of the form 2(ngamma) holds with high probability even when the number of clauses is n((k+2)-epsilon).
This paper presents an efficient synthesis algorithm and its proof of correctness for computing the controllable, nonblocking, and minimally restrictive supervisor in the supervisory control theory. Conventional synth...
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This paper presents an efficient synthesis algorithm and its proof of correctness for computing the controllable, nonblocking, and minimally restrictive supervisor in the supervisory control theory. Conventional synthesis algorithms are based on backward reachability computations, where blocking and uncontrollable states are iteratively found by searching the entire state space several times until a fixed point is reached. Many unnecessary states may be visited in this kind of searching. In this paper, we present an alternative synthesis algorithm based on forward reachability, where a number of synthesis steps are performed during the reachability computations. This approach is inspired from the search techniques in Artificial Intelligence ( AI) planning. To handle large-scale problems, the algorithm performs the computations symbolically based on binary decision diagrams. The algorithm has been developed, implemented, and applied to several large-scale benchmarks. It is shown that, on average, the on-the-fly algorithm is more efficient than the conventional synthesis algorithms, in particular for problems with many uncontrollable states.
Enriching many location-based applications, various new skyline queries are proposed and formulated based on the notion of locational dominance, which extends conventional one by taking objects' nearness to query ...
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Enriching many location-based applications, various new skyline queries are proposed and formulated based on the notion of locational dominance, which extends conventional one by taking objects' nearness to query positions into account additional to objects' nonspatial attributes. To answer a representative class of skyline queries for location-based applications efficiently, this paper presents two index-based approaches, namely, augmented R-tree and dominance diagram. Augmented R-tree extends R-tree by including aggregated nonspatial attributes in index nodes to enable dominance checks during index traversal. Dominance diagram is a solution-based approach, by which each object is associated with a precomputed nondominance scope wherein query points should have the corresponding object not locationally dominated by any other. Dominance diagram enables skyline queries to be evaluated via parallel and independent comparisons between nondominance scopes and query points, providing very high search efficiency. The performance of these two approaches is evaluated via empirical studies, in comparison with other possible approaches.
Nowadays, power system reconfiguration has received much interest and has achieved significant progress. Reconfiguration can be accomplished by modifying the status of the sectionalizing switches or tie switches. The ...
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Nowadays, power system reconfiguration has received much interest and has achieved significant progress. Reconfiguration can be accomplished by modifying the status of the sectionalizing switches or tie switches. The main objective of a network reconfiguration strategy is to reduce power loss, relieve overloading and improve load end voltage profile. This study reviews the advancement of power system reconfiguration research using graph theory including optimization-based approaches. In the context of determining the optimal radial network using graph theory-based strategies are also discussed. Network reconfiguration mechanism, which includes different graph theory analysis such as Prim's Minimal Spanning Tree, Dijkstra's Shortest Path Algorithm, Kruskal's Maximal Spanning Tree, Edmonds' Maximal Spanning Tree are presented. Four different code for the above graph theory techniques which already been implemented by previous researchers have been simulated and generate candidate solutions for 14 node system. The simulations demonstrate step by step procedure of the network reconfiguration mechanism. Moreover, simulation results verify that the graph theory approach can give good solution for Network reconfiguration with optimal radial network, less power loss and higher level of load voltage.
Most of the great success of heuristic search as an approach to AI Planning is due to the right design of domain-independent heuristics. Although many heuristic planners perform reasonably well, the computational cost...
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Most of the great success of heuristic search as an approach to AI Planning is due to the right design of domain-independent heuristics. Although many heuristic planners perform reasonably well, the computational cost of computing the heuristic function in every search node is very high, causing the planner to scale poorly when increasing the size of the planning tasks. For tackling this problem, planners can incorporate additional domain-dependent heuristics in order to improve their performance. Learning-based planners try to automatically acquire these domain-dependent heuristics using previous solved problems. In this work, we present a case-based reasoning approach that learns abstracted state transitions that serve as domain control knowledge for improving the planning process. The recommendations from the retrieved cases are used as guidance for pruning or ordering nodes in different heuristic search algorithms applied to planning tasks. We show that the CBR guidance is appropriate for a considerable number of planning benchmarks.
In this paper, process reengineering (PR) is presented as a constrained design search problem, where a solution is located using one of two alternative search algorithms. The algorithms are used to develop a framework...
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In this paper, process reengineering (PR) is presented as a constrained design search problem, where a solution is located using one of two alternative search algorithms. The algorithms are used to develop a framework for a PR decision support system (PRDSS). We believe that the result of our work lays the ground for a more orderly and structured definition and development of the PR concept.
This paper argues that computational grids can be used for far more types of applications than just trivially parallel ones. Algorithmic optimizations like latency-hiding and exploiting locality can be used effectivel...
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This paper argues that computational grids can be used for far more types of applications than just trivially parallel ones. Algorithmic optimizations like latency-hiding and exploiting locality can be used effectively to obtain high performance on grids, despite the relatively slow wide-area networks that connect the grid resources. Moreover, the bandwidth of wide-area networks increases rapidly, allowing even some applications that are extremely communication intensive to run on a grid, provided the underlying algorithms are latency-tolerant. We illustrate large-scale parallel computing on grids with three example applications that search large state spaces: transposition-driven search, retrograde analysis, and model checking. We present several performance results on a state-of-the-art computer science grid (DAS-3) with a dedicated optical network.
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