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67
A Simple Algorithm for Nearest Neighbor Search in High Dimensions
 IEEE Transactions on Pattern Analysis and Machine Intelligence
, 1997
"... Abstract—The problem of finding the closest point in highdimensional spaces is common in pattern recognition. Unfortunately, the complexity of most existing search algorithms, such as kd tree and Rtree, grows exponentially with dimension, making them impractical for dimensionality above 15. In ne ..."
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Cited by 126 (1 self)
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Abstract—The problem of finding the closest point in highdimensional spaces is common in pattern recognition. Unfortunately, the complexity of most existing search algorithms, such as kd tree and Rtree, grows exponentially with dimension, making them impractical for dimensionality above 15. In nearly all applications, the closest point is of interest only if it lies within a userspecified distance e. We present a simple and practical algorithm to efficiently search for the nearest neighbor within Euclidean distance e. The use of projection search combined with a novel data structure dramatically improves performance in high dimensions. A complexity analysis is presented which helps to automatically determine e in structured problems. A comprehensive set of benchmarks clearly shows the superiority of the proposed algorithm for a variety of structured and unstructured search problems. Object recognition is demonstrated as an example application. The simplicity of the algorithm makes it possible to construct an inexpensive hardware search engine which can be 100 times faster than its software equivalent. A C++ implementation of our algorithm is available upon request to search@cs.columbia.edu/CAVE/.
The computational complexity of decentralized discreteevent control problems
, 1993
"... Computational complexity results are obtained for decentralized discreteevent system problems. These results generalize the earlier work of Tsitsiklis, who showed that for centralized supervisory control problems (under partial observation), solution existence is decidable in polynomial time for a ..."
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Cited by 42 (4 self)
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Computational complexity results are obtained for decentralized discreteevent system problems. These results generalize the earlier work of Tsitsiklis, who showed that for centralized supervisory control problems (under partial observation), solution existence is decidable in polynomial time for a special type of problem but becomes computationally intractable for the general class. As in the case of centralized control, there is no polynomialtime algorithm for producing supervisor solutions.
Experience with distributed programming in Orca
 in Proc. IEEE CS International Conference on Computer Languages
, 1990
"... Orca is a language for programming parallel applications on distributed computing systems. Although processors in such systems communicate only through message passing and not through shared memory, data types and create instances (objects) of these types, which may be shared among processes. All op ..."
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Cited by 40 (10 self)
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Orca is a language for programming parallel applications on distributed computing systems. Although processors in such systems communicate only through message passing and not through shared memory, data types and create instances (objects) of these types, which may be shared among processes. All operations on shared objects are executed atomically. Orca’s shared objects are implemented by replicating them in the local memories of the processors. Read operations use the local copies of the object, without doing any interprocess communication. Write operations update all copies using an efficient reliable broadcast protocol. In this paper, we briefly describe the language and its implementation and then report on our experiences in using Orca for three parallel applications: the Traveling Salesman Problem, the Allpairs Shortest Paths problem, and Successive Overrelaxation. These applications have different needs for shared data: TSP greatly benefits from the support for shared data; ASP benefits from the use of broadcast communication, even though it is hidden in the implementation; SOR merely requires pointtopoint communication, but still can be implemented in the language by simulating message passing.
A Davidson program for finding a few selected extreme eigenpairs of a large, sparse, real, symmetric matrix
"... A program is presented for determining a few selected eigenvalues and their eigenvectors on either end of the spectrum of a large, real, symmetric matrix. Based on the Davidson method, which is extensively used in quantum chemistry/physics, the current implementation improves the power of the origin ..."
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Cited by 26 (11 self)
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A program is presented for determining a few selected eigenvalues and their eigenvectors on either end of the spectrum of a large, real, symmetric matrix. Based on the Davidson method, which is extensively used in quantum chemistry/physics, the current implementation improves the power of the original algorithm by adopting several extensions. The matrixvector multiplication routine that it requires is to be provided by the user. Different matrix formats and optimizations are thus feasible. Examples of an efficient sparse matrix representation and a matrixvector multiplication are given. Some comparisons with the Lanczos method demonstrate the efficiency of the program. PROGRAM SUMMARY Title of program: DVDSON Catalogue Number: To be assigned Program obtainable from: CPC Program Library, Queen's University of Belfast, N. Ireland (see application form in this issue). Licensing provisions: none Computer: Sun3/80, Sun SPARCstation IPC, Intel iPSC/860. Operating system: SunOS Rele...
Equalization Concepts for EDGE
 IEEE TRANSACTIONS ON WIRELESS COMMUNICATIONS
, 1999
"... In this paper, an equalization concept for the novel radio access scheme EDGE (Enhanced Data Rates for GSM Evolution) is proposed, by which high performance can be obtained at moderate computational complexity. Because highlevel modulation is employed in EDGE, optimum equalization as usually perfor ..."
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Cited by 25 (9 self)
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In this paper, an equalization concept for the novel radio access scheme EDGE (Enhanced Data Rates for GSM Evolution) is proposed, by which high performance can be obtained at moderate computational complexity. Because highlevel modulation is employed in EDGE, optimum equalization as usually performed in GSM (Global System for Mobile Communications) receivers is too complex, and suboptimum schemes have to be considered. It is shown that delayed decisionfeedback sequence estimation (DDFSE) and reducedstate sequence estimation (RSSE) are promising candidates. For various channel profiles, approximations for the bit error rate of these suboptimum equalization techniques are given and compared with simulation results for DDFSE. It turns out that a discretetime prefilter creating a minimumphase overall impulse response is indispensible for a favourable tradeoff between performance and complexity. Additionally, the influence of channel estimation and of the receiver input filter is investigated, and the reasons for performance degradation compared to the additive white Gaussian noise channel are indicated. Finally, the overall system performance attainable with the proposed equalization concept is determined for transmission with channel coding.
Automated Parallelization of Discrete Statespace Generation
 Journal of Parallel and Distributed Computing
, 1997
"... We consider the problem of generating a large statespace in a distributed fashion. Unlike previously proposed solutions that partition the set of reachable states according to a hashing function provided by the user, we explore heuristic methods that completely automate the process. The first step ..."
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Cited by 21 (2 self)
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We consider the problem of generating a large statespace in a distributed fashion. Unlike previously proposed solutions that partition the set of reachable states according to a hashing function provided by the user, we explore heuristic methods that completely automate the process. The first step is an initial random walk through the state space to initialize a search tree, duplicated in each processor. Then, the reachability graph is built in a distributed way, using the search tree to assign each newly found state to classes assigned to the available processors. Furthermore, we explore two remapping criteria that attempt to balance memory usage or future workload, respectively. We show how the cost of computing the global snapshot required for remapping will scale up for system sizes in the foreseeable future. An extensive set of results is presented to support our conclusions that remapping is extremely beneficial. 1 Introduction Discrete systems are frequently analyzed by genera...
On Indexing Sliding Windows over Online Data Streams
 In EDBT
, 2004
"... Abstract. We consider indexing sliding windows in main memory over online data streams. Our proposed data structures and query semantics are based on a division of the sliding window into subwindows. By classifying windowed operators according to their method of execution, we motivate the need for ..."
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Cited by 18 (4 self)
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Abstract. We consider indexing sliding windows in main memory over online data streams. Our proposed data structures and query semantics are based on a division of the sliding window into subwindows. By classifying windowed operators according to their method of execution, we motivate the need for two types of windowed indices: those which provide a list of attribute values and their counts for answering setvalued queries, and those which provide direct access to tuples for answering attributevalued queries. We propose and evaluate indices for both of these cases and show that our techniques are more efficient than executing windowed queries without an index. 1
On Crossing Minimization Problem
, 1998
"... In this paper we consider a problem related to global routing postoptimization: the crossing minimization problem (CMP). Given a global routing representation, the CMP is to minimize redundant crossings between every pair of nets. In particular, there are two kinds of CMP: constrained CMP (CCMP) an ..."
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Cited by 17 (4 self)
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In this paper we consider a problem related to global routing postoptimization: the crossing minimization problem (CMP). Given a global routing representation, the CMP is to minimize redundant crossings between every pair of nets. In particular, there are two kinds of CMP: constrained CMP (CCMP) and unconstrained CMP (UCMP). These problems have been studied previously in [Groe89], where an O(m 2 n) algorithm was proposed for CCMP, and in [MS95], where an (mn 2 +¸ 2 ) algorithm was proposed for UCMP, where m is the total number of modules, n is the number of nets, and ¸ is the number of crossings defined by an initial global routing topology. We present a simpler and faster O(mn) algorithm for CCMP and an O(n(m + ¸)) time algorithm for UCMP. Both algorithms improve over the time bounds of the previously proposed algorithms. The novel part of our algorithm is that it uses the plane embedding information of globally routed nets in the routing area to construct a graphbased framewo...
Cache Investment: Integrating Query Optimization and Distributed Data Placement
 ACM TODS
, 2000
"... Emerging distributed query processing systems support... In this paper, we propose Cache Investment mechanisms and policies and analyze their performance. The analysis uses results from both an implementation on the SHORE storage manager and a detailed simulation model. Our results show that Cache I ..."
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Cited by 17 (2 self)
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Emerging distributed query processing systems support... In this paper, we propose Cache Investment mechanisms and policies and analyze their performance. The analysis uses results from both an implementation on the SHORE storage manager and a detailed simulation model. Our results show that Cache Investment can significantly improve the overall performance of a system and demonstrate the tradeoffs among various alternative policies.
Efficient construction of pipelined multibittrie RouterTables
 IEEE Trans. Comput
, 2003
"... Efficient algorithms to construct multibit tries suitable for pipelined routertable applications are developed. We first enhance the 1phase algorithm of Basu and Narlikar [1] obtaining a 1phase algorithm that is 2.5 to 3 times as fast. Next we develop 2phase algorithms that not only guarantee to ..."
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Cited by 15 (1 self)
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Efficient algorithms to construct multibit tries suitable for pipelined routertable applications are developed. We first enhance the 1phase algorithm of Basu and Narlikar [1] obtaining a 1phase algorithm that is 2.5 to 3 times as fast. Next we develop 2phase algorithms that not only guarantee to minimize the maximum perstage memory but also guarantee to use the least total memory subject to the former constraint. Our 2phase algorithms not only generate better pipelined trees than generated by the 1phase algorithm but they also take much less time. A node pullup scheme that guarantees no increase in maximum perstage memory as well as a partitioning heuristic that generates pipelined multibit tries requiring less maximum perstage memory than required by the tries obtained using the 1phase and 2phase algorithms also are proposed.