36819476
Efficient Parallel Algorithms on Distance Hereditary Graphs
Distance hereditary graphs are graphs in which every two vertices have the same distance in every connected induced subgraph containing them. In this paper, we study properties of distance hereditary graphs from the view point of parallel computations. We present efficient parallel algorithms for finding a minimum weighted connected dominating set, a minimum weighted Steiner tree, which take O(log n) time using O(n + m) processors on CRCW PRAM, where n and m are the number of vertices and edges of a given graph, respectively. We also find a maximum weighted clique of a distance hereditary graph in O(log2 n) time using O(n + m) processors on a CREW PRAM.
1980858
Edge and Node Searching Problems on Trees
In this paper, we show that there is a natural correspondence between a tree's edge-search strategy and its node-search strategy. By doing so, we simplify the previous linear time algorithm for determining the edge-search number of a tree, and improve the running time of a previous algorithm for constructing an edge-search strategy (or plan) for a tree containing n vertices from O(n log n) to O(n) time.
16976049
Efficient Broadcasting in Wormhole-Routed Multicomputers: A Network-Partitioning Approach
In this paper, a network-partitioning approach for one-to-all broadcasting on wormhole-routed networks is proposed. To broadcast a message, the scheme works in three phases. First, a number of data-distributing networks (DDNs), which can work independently, are constructed. Then the message is evenly divided into submessages, each being sent to a representative node in one DDN. Second, the submessages are broadcast on the DDNs concurrently. Finally, a number of data-collecting networks (DCNs), which can work independently too, are constructed. Then, concurrently on each DCN, the submessages are collected and combined into the original message. Our approach, especially designed for wormhole-routed networks, is conceptually similar but fundamentally very different from the traditional approach of using multiple edge-disjoint spanning trees in parallel for broadcasting in store-and-forward networks. One interesting issue is on the definition of independent DDNs and DCNs, in the sense of wormhole routing. We show how to apply this approach to tori, meshes, and hypercubes. Thorough analyses and comparisons based on different system parameters and configurations are conducted. The results do confirm the advantage of our scheme, under various system parameters and conditions, over other existing broadcasting algorithms.
12861854
The Recognition of Geodetically Connected Graphs
Abstract Let G = ( V , E ) be a graph with vertex set V of size n and edge set E of size m . A vertex υ ϵ V is called a hinge vertex if the distance of any two vertices becomes longer after v is removed. A graph without hinge vertex is called a hinge-free graph. In general, a graph G is k -geodetically connected or k -GC for short if G can tolerate any k − 1 vertices failures without increasing the distance among all the remaining vertices. In this paper, we show that recognizing a graph G to be k -GC for the largest value of k can be solved in O ( nm ) time. In addition, more efficient algorithms for recognizing the k -GC property on some special graphs are presented. These include the O ( n + m ) time algorithms on strongly chordal graphs (if a strong elimination ordering is given), ptolemaic graphs, and interval graphs, and an O ( n 2 ) time algorithm on undirected path graphs (if a characteristic tree model is given). Moreover, we show that if the input graph G is not hinge-free then finding all hinge vertices of G can be solved in the same time complexity on the above classes of graphs.
17202338
Fault-Free Hamiltonian Cycles in Faulty Arrangement Graphs
The arrangement graph A/sub n,k/, which is a generalization of the star graph (n-k=1), presents more flexibility than the star graph in adjusting the major design parameters: number of nodes, degree, and diameter. Previously, the arrangement graph has proved Hamiltonian. In this paper, we further show that the arrangement graph remains Hamiltonian even if it is faulty. Let |F/sub e/| and |F/sub v/| denote the numbers of edge faults and vertex faults, respectively. We show that A/sub n,k/ is Hamiltonian when 1) (k=2 and n-k/spl ges/4, or k/spl ges/3 and n-k/spl ges/4+[k/2]), and |F/sub e/|/spl les/k(n-k)-2, or 2) k/spl ges/2, n-k/spl ges/2+[k/2], and |F/sub e/|/spl les/k(n-k-3)-1, or 3) k/spl ges/2, n-k/spl ges/3, and |F/sub e/|/spl les/k, or 4) n-k/spl ges/3 and |F/sub v/|/spl les/n-3, or 5) n-k/spl ges/3 and |F/sub v/|+|F/sub e/|/spl les/k. Besides, for A/sub n,k/ with n-k=2, we construct a cycle of length at least 1) [n!/(n-k!)]-2 if |F/sub e/|/spl les/k-1, or 2) [n!/(n-k)!]-|F/sub v/|-2(k-1) if |F/sub v/|/spl les/k-1, or 3) [n!/(n-k)!]-|F/sub v/|-2(k-1) if |F/sub e/|+|F/sub v/|/spl les/k-1, where [n!/(n-k)!] is the number of nodes in A/sub n,k/.
44408883
Hamiltonian-laceability of star graphs
8958554
Nested mappings: schema mapping reloaded
Many problems in information integration rely on specifications, called schema mappings, that model the relationships between schemas. Schema mappings for both relational and nested data are well-known. In this work, we present a new formalism for schema mapping that extends these existing formalisms in two significant ways. First, our nested mappings allow for nesting and correlation of mappings. This results in a natural programming paradigm that often yields more accurate specifications. In particular, we show that nested mappings can naturally preserve correlations among data that existing mapping formalisms cannot. We also show that using nested mappings for purposes of exchanging data from a source to a target will result in less redundancy in the target data. The second extension to the mapping formalism is the ability to express, in a declarative way, grouping and data merging semantics. This semantics can be easily changed and customized to the integration task at hand. We present a new algorithm for the automatic generation of nested mappings from schema matchings (that is, simple element-to-element correspondences between schemas). We have implemented this algorithm, along with algorithms for the generation of transformation queries (e.g., XQuery) based on the nested mapping specification. We show that the generation algorithms scale well to large, highly nested schemas. We also show that using nested mappings in data exchange can drastically reduce the execution cost of producing a target instance, particularly over large data sources, and can also dramatically improve the quality of the generated data.
44418101
Degree-constrained minimum spanning tree
Abstract In this paper the problem of a degree-constrained minimum spanning tree (DCMST) is defined. The problem is formulated as a linear 0–1 integer programming problem. A primal and a dual heuristic (construction) procedure and a branch-and-bound algorithm are proposed to construct a DCMST. These procedures are illustrated with a simple example. Some computational experience with these algorithms is also reported.
13524203
Haptic discrimination of force direction and the influence of visual information
Despite a wealth of literature on discrimination thresholds for displacement, force magnitude, stiffness, and viscosity, there is currently a lack of data on our ability to discriminate force directions. Such data are needed in designing haptic rendering algorithms where force direction, as well as force magnitude, are used to encode information such as surface topography. Given that haptic information is typically presented in addition to visual information in a data perceptualization system, it is also important to investigate the extent to which the congruency of visual information affects force-direction discrimination. In this article, the authors report an experiment on the discrimination threshold of force directions under the three display conditions of haptics alone (H), haptics plus congruent vision (HVcong), and haptics plus incongruent vision (HVincong). Average force-direction discrimination thresholds were found to be 18.4°, 25.6°, and 31.9° for the HVcong, H and HVincong conditions, respectively. The results show that the congruency of visual information significantly affected haptic discrimination of force directions, and that the force-direction discrimination thresholds did not seem to depend on the reference force direction. The implications of the results for designing haptic virtual environments, especially when the numbers of sensors and actuators in a haptic display do not match, are discussed.
34381900
Using spatial warning signals to capture a driver's visual attention
This study was designed to assess the potential benefits of using spatial auditory or vibrotactile warning signals in the domain of driving performance, using a simulated driving task. Across six experiments, participants had to monitor a rapidly presented stream of distractor letters for occasional target digits (simulating an attention-demanding visual task, such as driving). Whenever participants heard an auditory cue (E1-E4) or felt a vibration (E5-E6), they had to check the front and the rearview mirror for the rapid approach of a car from in front or behind and respond accordingly (either by accelerating or braking). The efficacy of various auditory and vibrotactile warning signals in directing a participant's visual attention to the correct environmental position was compared (see Table 1). The results demonstrate the potential utility of semantically-meaningful or spatial auditory, and/or vibrotactile warning signals in interface design for directing a driver's, or other interface-operator's, visual attention to time-critical events or information.
1145137
Agent-assisted collaborative concept map
Merlin is a collaborative concept map that enables students to discuss their ideas. The agent in Merlin aims to monitor the students' content of discussion in order to provide context-sensitive help. Keywords in the students' discussion in a chat box are compared to the knowledge domain and appropriate support material is adapted to the student model. Instructional media is generated using design patterns.