Decentralized fuzzy control of multiple nonholonomic vehicles This work considers the problem of controlling multiple nonholonomic vehicles so that they converge to a scent source without colliding with each other. Since the control is to be implemented on a simple 8-bit microcontroller, fuzzy control rules are used to simplify a linear quadratic regulator control design. The inputs to the fuzzy controllers for each vehicle are the noisy direction to the source, the distance to the closest neighbor vehicle, and the direction to the closest vehicle. These directions are discretized into four values: Forward, Behind, Left, and Right; and the distance into three values: Near, Far, and Gone. The values of the control at these discrete values are obtained based on the collision-avoidance repulsive forces and an attractive force towards the goal. A fuzzy inference system is used to obtain control values for inputs between the small number of discrete input values. Simulation results are provided which demonstrate that the fuzzy control law performs well compared to the exact controller. In fact, the fuzzy controller demonstrates improved robustness to noise. The distributed control of multiple robotic vehicles has been a subject of significant recent interest. When hundreds or thousands of such vehicles are involved, clearly to be cost effective each vehicle must be cheap. Thus, sensors are likely to be cheap, and therefore noisy, and the amount of compute power and memory on board each vehicle is likely to be small. This brings about the need to be able to have robustness to noisy sensor measurements while simultaneously using a simple controller. Kalman filters can be relatively expensive to implement, in terms of required computation power and memory. Fuzzy control provides an alternative approach.. There has been much work in multiple mobile robotic vehicle problems, much of which has not considered the use of fuzzy logic. Asama [2] intelligently points out that "an autonomous and decentralized system has two essentially contradictory characteristics, autonomy and cooperativeness, and the biggest problem in the study of distributed autonomous robotic systems is how to reconcile these two features." Reynolds [ 151 considered the formation of flocks, herds, and schools in simulations in which multiple autonomous agents were driven away from each other and other obstacles by inverse square law repulsive forces. Arkin [l] studied an approach to "cooperation without communication," for multiple mobile robots that are supposed to forage and retrieve objects in a hostile environment. Kube and Zhang [9] also considered decentralized robots performing tasks "without explicit communication.". Much of their study examined comparisons of behaviors of different social insects such as ants and bees. They considered a box-pushing task and utilized a Subsumption approach [3, 41 as well as ALN (Adaptive Logic Networks).. Noreils [ 141 conducted work toward achieving cooperation between mobile robots for indoor environment applications. He dealt with robots that were not necessarily homogeneous. That is, one subset of the robots may have capabilities that another subset does not have. His architecture consisted of three levels: functional level, control level, and planner level. The planner level was the high-level decision maker. Chen and Luh [5] examined decentralized control laws that drove a set of mobile robots into a specific formation.. In particular, a circle formation was considered. Similarly, Yamaguchi and Arai [ 171 studied line-formations, and so did Yoshida et al, [18] .. In this paper, we are interested in designing a fuzzy controller with predictable convergence characteristics. Previous work involving fuzzy control of robotic vehicles generated fuzzy rules whose convergence characteristics are not predictable (see Maeda et a1 [lo] and Marapane et a1 [ 111) . Instead, we want to create fuzzy controllers with predictable convergence characteristics.. The work herein considers the problem of controlling multiple nonholonomic robotic vehicles which converge to a scent source without collisions between vehicles, in the presence of noisy measurements and a 0-7803-4530-4198 $10.00 0 1998 AACC small amount of compute-power and memory on board each vehicle.. In Section 2, the problem statement is given. Section 3 describes the linear quadratic control law, which is then fuzzified in Section 4. Section 5 presents simulation results, and Section 6 compares the controllers to a controller that uses a Kalman estimator. Finally, conclusions are given in Section 7. This work investigated decentralized fuzzy control of multiple nonholonomic vehicles. An LQR controller was designed using a change of variables that reduced the control problem from one with three degrees of freedom to a non-singular one with only two degrees of freedom. Fuzzy control was investigated because the control is to be implemented on a simple 8-bit microcontroller in the future. The fuzzy controller exhibited a smoother response than the LQR controller in the presence of noisy measurements and its smoothness and performance compared favorably to a controller that used a Kalman estimator.

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Generalized Coincident Pulse Technique and New Addressing Schemes for Time-Division Multiplexing Optical Buses Time-division multiplexing (TDM) optical buses have applications in computer networks, high-performance routers and switches, and interprocessor communication subsystems of parallel computers. Three waveguides are used to implement the previously proposed TDM optical bus. One waveguide is used for data transmission, and the other two waveguides are used for processor addressing. The coincident pulse technique is used to implement a unary addressing scheme. This architecture has two drawbacks: the bandwidth of address waveguides is wasted and the scalability of the bus is limited due to the unary addressing. In this paper, the coincident pulse technique is generalized in order to derive compact addressing schemes for TDM optical buses. Based on this new technique, optimal addressing schemes are presented. Several general methods for designing new addressing schemes are proposed to achieve various trade-offs. Compared with the previously proposed addressing scheme, the new schemes significantly improve the utilization of the bandwidth of optical waveguides and the scalability of a TDM optical bus.Academic Press

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Co-Authorship Networks in the Digital Library Research Community The field of digital libraries (DLs) coalesced in 1994: the first digital library conferences were held that year, awareness of the World Wide Web was accelerating, and the National Science Foundation awarded $24 Million (U.S.) for the Digital Library Initiative (DLI). In this paper we examine the state of the DL domain after a decade of activity by applying social network analysis to the co-authorship network of the past ACM, IEEE, and joint ACM/IEEE digital library conferences. We base our analysis on a common binary undirectional network model to represent the co-authorship network, and from it we extract several established network measures. We also introduce a weighted directional network model to represent the co-authorship network, for which we define AuthorRank as an indicator of the impact of an individual author in the network. The results are validated against conference program committee members in the same period. The results show clear advantages of PageRank and AuthorRank over degree, closeness and betweenness centrality metrics. We also investigate the amount and nature of international participation in Joint Conference on Digital Libraries (JCDL).

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Subset construction complexity for homogeneous automata, position automata and ZPC-structures The aim of this paper is to investigate how subset construction performs on specific families of automata. A new upper bound on the number of states of the subset-automaton is established in the case of homogeneous automata. The complexity of the two basic steps of subset construction, i.e. the computation of deterministic transitions and the set equality tests, is examined depending on whether the nondeterministic automaton is an unrestricted one, an homogeneous one, a position one or a ZPC-structure, which is an implicit construction for a position automaton. Automata determinization may be exponential, whereas most of automata operations are polynomial. It is not possible to avoid this behaviour in the general case [16] . It is nevertheless important to carefully handle the implementation of the determinization algorithm when designing automata software tools, in order to preserve as well as possible the performances of the whole system. Two basic computation steps are carried on all along the determinization process: the computation of a deterministic transition, which yields a subset of the set of nondeterministic states, and set equality testing which makes it possible to decide whether a deterministic transition generates a new state or not.. Concerning the computation of the set of deterministic transitions, the choice of the data structure implementing the set of nondeterministic transitions has much influence on the complexity. Softwares such as AUTOMATE [3] , INR [6] and GRAIL [17] make use of a representation in which both transitions with the same origin and transitions with the same origin and the same symbol are contiguous. Johnson and Wood [7] have studied the efficiency of various sorting procedures applied to subsets computed from such data structures.. On the other hand, the choice of the data structure encoding subsets has a significant influence on the complexity of set equality testing. The number of integer comparisons involved by the overall set equality tests is O( √ n2 2n ) when using lists and O(n 2 log(n)2 n ) when using balanced search trees [15] . There exist investigations that are motivated by the will to improve such complexities, for instance Leslie et al. [9, 10] .. The aim of this paper is to investigate how subset construction performs on specific automata, in particular on position automata. The position automaton of a regular expression is defined by the algorithm described in [4] and in [11] . The author and his co-researchers [20, 13] have designed a linear space and time representation of the position automaton of a regular expression, which is based on two state forests connected by a set of links. The so-called ZPCstructure leads to an output sensitive implementation of the conversion of a regular expression into an automaton and to an efficient algorithm for testing the membership of a word to a regular language [15] .. The impact that the specific properties of position automata have on subset construction are analyzed. Firstly, a position automaton is homogeneous and we establish a new upper bound on the number of states of the automaton resulting from the determinization of an homogeneous automaton; this bound is much smaller in many cases than the standard 2 n − 1 bound which holds for unrestricted automata. We also give an estimation of the complexity of the transition computation and of the set equality testing in the case of an homogeneous automaton. Secondly, a position automaton can be implemented as a ZPC-structure, whose main feature is to allow the computation of disjoint unions of transition sets thanks to a specific encoding of position sets. We show how to make use of this representation in order to reduce the complexity of the two basic steps of the determinization process.. Basic definitions and useful notations are gathered together in the next section. Section 3 recalls how subset construction performs on unrestricted automata, and analyzes its complexity. Section 4 deals with homogeneous automata, section 5 with position automata and section 6 with ZPC-structures. In each of these sections, algorithmic refinements of subset construction are provided, as well as new complexity bounds. The homogeneity property significantly reduces the number of deterministic states; as a consequence, the complexity of the transition computation and of the set equality testing is generally much lower for homogeneous automata than for unrestricted automata. This complexity can be lessened still further in the case of position automata as far as computation is carried out on the ZPCstructure whose main feature is to allow the computation of transition sets via disjonctive unions.. procedure create-γ(Φ , F irsts(E), γ) /* Φ and F irsts(E) are input parameters */ /* γ is an output parameter */ /* d is a local boolean array */ function dans(ϕ, in) /* ϕ is a node of T (E) and is used as an input parameter */ /* in is a boolean array and is used as an input/output parameter */ begin if (in[ϕ] = false) or (ϕ ∈ P os(E)) then switch ϕ case '·','+' : in

B I O O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I O O O O B I O O O O O O O O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I O O B I O O O O O B O O O O O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O


Cyclic Sequence Alignments: Approximate Versus Optimal Techniques The problem of cyclic sequence alignment is considered. Most existing optimal methods for comparing cyclic sequences are very time consuming. For applications where these alignments are intensively used, optimal methods are seldom a feasible choice. The alternative to an exact and costly solution is to use a close-to-optimal but cheaper approach. In previous works, we have presented three suboptimal techniques inspired on the quadratic-time suboptimal algorithm proposed by Bunke and Bühler. Do these approximate approaches come sufficiently close to the optimal solution, with a considerable reduction in computing time? Is it thus worthwhile investigating these approximate methods? This paper shows that approximate techniques are good alternatives to optimal methods. It is often necessary to compare two or more sequences, and measure the extent to which they differ. A basic approach is to analyze the total difference between two sequences, regarding a collection of individual elementary differences, usually, substitutions, deletions and insertions. They are known as edit operations, because they operate over a source sequence by actively changing (editing) it into a target sequence. Levenshtein 5 introduced a distance from one sequence x to another sequence y, δ(x, y), defined as the smallest number of edit operations to change x into y. One widely adopted generalization to the Levenshtein metric is to weigh the edit operations. It is defined as a minimum-weighted sequence of transforming x into y. The optimization procedure for computing (weighted) edit distances falls within the framework of dynamic programming. The general algorithm, that was reported in Ref. 10 , among many others, requires a computing time that is quadratic in the length of the sequences.. An interesting extension of the previous method considers a string x as a cyclic string. A cyclic string x is an equivalence class, denoted by [x] , defined by the following equivalent relation: x ≡ x ⇔ x = σ k (x), for some k ∈ N, where σ k (x) = x k+1 x k+2 · · · x |x| x 1 · · · x k . Given two cyclic strings [x] and [y], the cyclic distance δ C between them is defined as. In the same way, the edit distance between a linear string x and a cyclic string [y] can also be defined by. The following lemma 6 presents a more efficient way to compute the edit distance between cyclic strings by requiring a cubic time computation complexity. A Divide and Conquer approach was presented in Ref. 6 (MA) to efficiently compute the optimal cyclic alignment between two strings x and y, where |x| represents the length of x, reducing the computational complexity from cubic to O(|x||y| log |y|) in the worst case. Another algorithm for cyclic string matching was introduced in Ref. 4 (GT) . It has a theoretical cubic time complexity but, its practical execution time may be significantly lower. The MA carries out an exhaustive scanning of a Divide and Conquer binary partition of the solution space. A Branch and Bound strategy based on the Maes approach was proposed in Ref. 7 , to explore only those promising branches that may lead to the optimal solution. Two lower bound functions (MB1 and MB2) are introduced for the best possible solution which can be reached from a current state. Both versions keep the worst case complexity of the Maes approach, but they always compute the optimal solution faster than MA and GT.. On the other hand, by sacrificing the strict optimality of the solution, another way to efficiently deal with this problem arises. An O(|x||y|) suboptimal method was proposed in Ref. 2 (BBA). In Refs. 8 and 9 we proposed three new approximate approaches inspired on the BBA. These previous works showed that our suboptimal methods are much more accurate than BBA, closely approaching the optimal solution. But, how much faster are the approximate solutions obtained with respect to the computation of the exact solution? Is it worthwhile to use an estimation instead of the exact distance value? This article attempts to show that approximate techniques are good alternatives to optimal methods. The experiments were limited to the cyclic use of the Levenshtein metric, i.e. unit-weight insertions, deletions and substitutions. In this contribution, the problem of cyclic sequence alignment was considered. An extensive comparison among the better known exact algorithms, and three suboptimal (but faster) methods proposed by the authors in previous works, has been carried out. Experiments on both synthetic and real data demonstrated the usefulness of our approaches regarding both, accuracy and computing time.

O O O O O O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O


On Relating Functional Specifications to Architectural Specifications: A Case Study Software architecture specifications are predominantly concerned with describing the component structure of systems and how the components interact behaviorally. Little attention has been paid to formally relating those specifications to higher levels of specification, such as the system requirements. In this paper we present our progress toward addressing an instance of this problem, namely relating state-based software architecture specifications to high-level functional specifications. Our approach is to use an intermediate specification given in terms of a set of temporal logic properties to bridge the gap between the two levels of specifications. We describe our approach in the context of a particular case study, the AEGIS GeoServer Simulation Testbed system, showing how a compact functional specification of a critical behavioral property of the system can be used to validate three alternative architectural specifications of that system. A software architecture specification describes the high-level design of a system in terms of the structural and communication relationships of its components. At this level of description, the specification focuses on the interaction behaviors exhibited by the components, not the algorithms used internally by components to carry out their functional roles.. It is believed that having such design specifications for complex systems can improve the effectiveness of the development process and the quality of the final product by permitting analyses to be performed early in the life cycle [5, 13, 23] . Consequently, much effort has been devoted to researching, experimenting with, and categorizing the kinds of analyses that can be performed and the product quality attributes that can be improved through them [1, 3, 4, 7, 8, 9, 14, 15, 17, 18, 19, 21, 22] .. Despite the significant amount of research in architectural specification, there has been little attempt to formally relate it to higher levels of specification, such as the system requirements [24] . Only recently has interest begun to emerge in this regard [16, 20] . In this paper we present our progress toward addressing an instance of this problem, namely relating high-level functional specifications to software architecture specifications. We describe our approach in the context of a particular case study, the AEGIS GeoServer Simulation Testbed (AGST) system [2, 12] , showing how a compact functional specification of a critical behavioral property of the system can be used to validate three alternative architectural specifications of that system.. The basis for the method is the construction of a set of temporal logic properties that bridge the gap between the functional specification and the architectural specification. In essence, the temporal logic properties make explicit and visible the relevant behavioral dependencies that are inherent in the functional specification and that are deeply buried within the complex state descriptions of the architectural specification. Of course, both the functional and architectural specifications are abstractions, and as such they embody simplifying assumptions. These assumptions appear both at the level of individual components (i.e., so-called "black-box" assumptions) and at the level of the global architecture. The process of relating the functional and architectural specifications helps the analyst understand the interplay of the assumptions operating at these two levels.. The temporal logic properties developed here are given using the CTL formalism [10, 11] . This is a well-known branching logic for which model checkers are available. To specify software architectures, we use the CHAM (CHemical Abstract Machine) formalism [6] . This formalism has been used extensively by us and others in previous work on architectural specification and analysis [9, 14, 15, 25] . Note, however, that the general approach we describe in this paper is not tied to the CHAM formalism. For those unfamiliar with CHAM or its use in specifying software architectures, Appendix A provides a brief review. Appendix A also provides a brief review of CTL.. In the next section of the paper we introduce the subject of our case study, AGST. We also provide the functional specification that captures the property of concern. In Section 3 we give the CHAM specifications of three architectural variants of AGST. The CTL specifications that relate the architectural variants to the functional specification are presented in Section 4. We conclude in Section 5 with a discussion of future work. The relationship between architecture and design has been a long-standing subject of discussion. What has emerged is an understanding that "architecture" should refer to high levels of design that can be related to lower levels of design through suitable refinement steps. This seems reasonable, since software architectures represent the first system abstraction in which a (high level) description of the system implementation is provided, and that its structure and behavior should be prescriptive with respect to the implementation. The relationship between architecture and requirements is, by contrast, less clear. On one side there is the awareness that requirements and architectures should be related [24] . On the other there is the difficulty of relating very different concerns, modeled in different ways.. In this paper we tackled an instance of this problem by showing how a requirement on the data coherency of a system, modeled in a functional way, can be related to three variants of a software architecture, modeled in an operational, state-based style. At a very basic level, our approach is a kind of model checking, since it considers the requirement as a property that has to be related to a model of the implementation. This is a straightforward approach and there is no new insight in and of itself. What is novel in our approach is the way we build the formula that represents the relationship between the requirement and the architecture. In particular, we translate the requirement into a form that constraints the states of the architectural model. This is the most difficult part of our work, and the way we carried it out follows a logical path that allows us to easily prove that the formula is satisfied by the model. In other words, in building the formula we also performed the bulk of the proof. In more formal terms, we performed a proof by construction.. This suggests a future line of research in the direction of (semi-)automating the approach presented here. The idea is to formalize our methodology so that, starting from a functional requirement and from a basic set of mappings (e.g., basic functionalities on components, inputs/outputs on states, etc.) it can be possible to automatically build sub-formulae by model checking. Then the formulae can be composed together as suggested in our approach by using suitable logical and temporal operators. This would ease the task of relating very different models and, thus, allow early validation of software architectures with respect to complex functional constraints.

O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B O B I O O O O O O


Adaptive Mixture Methods Based on Bregman Divergences We investigate adaptive mixture methods that linearly combine outputs of m constituent filters running in parallel to model a desired signal. We use "Bregman divergences" and obtain certain multiplicative updates to train the linear combination weights under an affine constraint or without any constraints. We use unnormalized relative entropy and relative entropy to define two different Bregman divergences that produce an unnormalized exponentiated gradient update and a normalized exponentiated gradient update on the mixture weights, respectively. We then carry out the mean and the mean-square transient analysis of these adaptive algorithms when they are used to combine outputs of m constituent filters. We illustrate the accuracy of our results and demonstrate the effectiveness of these updates for sparse mixture systems. In this paper, we study adaptive mixture methods based on "Bregman divergences" [1, 2] that combine outputs of m constituent filters running in parallel on the same task. The overall system has two stages [3] [4] [5] [6] [7] [8] . The first stage contains adaptive filters running in parallel to model a desired signal. The outputs of these adaptive filters are then linearly combined to produce the final output of the overall system in the second stage. We use Bregman divergences and obtain certain multiplicative updates [9] , [2] , [10] to train these linear combination weights under an affine constraint [11] or without any constraints [12] .. We use unnormalized [2] and normalized relative entropy [9] to define two different Bregman divergences that produce the unnormalized exponentiated gradient update (EGU) and the exponentiated gradient update (EG) on the mixture weights [9] , respectively. We then perform the mean and the meansquare transient analysis of these adaptive mixtures when they are used to combine outputs of m constituent filters. We emphasize that to the best of our knowledge, this is the first mean and mean-square transient analysis of the EGU algorithm and the EG algorithm in the mixture framework (which naturally covers the classical framework also [13, 14] ). We illustrate the accuracy of our results through simulations in different configurations and demonstrate advantages of the introduced algorithms for sparse mixture systems.. Adaptive mixture methods are utilized in a wide range of signal processing applications in order to improve the steady-state and/or convergence performance over the constituent filters [11, 12, 15] . An adaptive convexly constrained mixture of two filters is studied in [15] , where the convex combination is shown to be "universal" such that the combination performs at least as well as its best constituent filter in the steady-state [15] . The transient analysis of this adaptive convex combination is studied in [16] , where the time evolution of the mean and variance of the mixture weights is provided. In similar lines, an affinely constrained mixture of adaptive filters using a stochastic gradient update is introduced in [11] . The steady-state mean square error (MSE) of this affinely constrained mixture is shown to outperform the steady-state MSE of the best constituent filter in the mixture under certain conditions [11] .. The transient analysis of this affinely constrained mixture for m constituent filters is carried out in [17] . The general linear mixture framework as well as the steady-state performances of different mixture configurations are studied in [12] .. In this paper, we use Bregman divergences to derive multiplicative updates on the mixture weights. We use the unnormalized relative entropy and the relative entropy as distance measures and obtain the EGU algorithm and the EG algorithm to update the combination weights under an affine constraint or without any constraints. We then carry out the mean and the mean-square transient analysis of these adaptive mixtures when they are used to combine m constituent filters. We point out that the EG algorithm is widely used in sequential learning theory [18] and minimizes an approximate final estimation error while penalizing the distance between the new and the old filter weights.. In network and acoustic echo cancellation applications, the EG algorithm is shown to converge faster than the LMS algorithm [14, 19] when the system impulse response is sparse [13] . Similarly, in our simulations, we observe that using the EG algorithm to train the mixture weights yields increased convergence speed compared to using the LMS algorithm to train the mixture weights [11, 12] when the combination favors only a few of the constituent filters in the steady state, i.e., when the final steady-state combination vector is sparse. We also observe that the EGU algorithm and the LMS algorithm show similar performance when they are used to train the mixture weights even if the final steady-state mixture is sparse.. To summarize, the main contributions of this paper are as follows:. • We use Bregman divergences to derive multiplicative updates on affinely constrained and unconstrained mixture weights adaptively combining outputs of m constituent filters.. • We use the unnormalized relative entropy and the relative entropy to define two different Bregman divergences that produce the EGU algorithm and the EG algorithm to update the affinely constrained and unconstrained mixture weights.. • We perform the mean and the mean-square transient analysis of the affinely constrained and unconstrained mixtures using the EGU algorithm and the EG algorithm.. The organization of the paper is as follows. In Section II, we first describe the mixture framework. In Section III, we study the affinely constrained and unconstrained mixture methods updated with the EGU algorithm and the EG algorithm. In Section IV, we first perform the transient analysis of the affinely constrained mixtures and then continue with the transient analysis of the unconstrained mixtures. Finally, in Section V, we perform simulations to show the accuracy of our results and to compare performances of the different adaptive mixture methods. The paper concludes with certain remarks in Section VI. In this paper, we investigate adaptive mixture methods based on Bregman divergences combining outputs of m adaptive filters to model a desired signal.. We use the unnormalized relative entropy and relative entropy as distance measures that produce the exponentiated gradient update with unnormalized weights (EGU) and the exponentiated gradient update with positive and negative weights (EG) to train the mixture weights under the affine constraints or without any constraints. We provide the transient analysis of these methods updated with the EGU and EG algorithms. In our simulations, we compare performances of the EG, EGU and LMS algorithms and observe that the EG algorithm performs better than the EGU and LMS algorithms when the combination vector in steady-state is sparse. We observe that the EGU and LMS algorithms show similar performance when they are used to train the mixture weights. We also observe a close agreement between the simulations and our theoretical results.

B I O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O


Complexity of manipulation, bribery, and campaign management in Bucklin and fallback voting Abstract A central theme in computational social choice is to study the extent to which voting systems computationally resist manipulative attacks seeking to influence the outcome of elections, such as manipulation (i.e., strategic voting), control, and bribery. Bucklin and fallback voting are among the voting systems with the broadest resistance (i.e., NP-hardness) to control attacks. However, only little is known about their behavior regarding manipulation and bribery attacks. We comprehensively investigate the computational resistance of Bucklin and fallback voting for many of the common manipulation and bribery scenarios; we also complement our discussion by considering several campaign-management problems for these two voting rules. We have given an in-depth study of the complexity of manipulation, bribery, and campaign management for Bucklin and fallback voting. Our results complement those regarding control, campaign management, and possible/necessary winner problems and, in effect, we now have an almost complete picture of the (worst-case) complexity of Bucklin and fallback voting for all the standard election problems (there is only a single result missing for one of the control problems). Having this complete picture is particularly useful for Bucklin and fallback voting: For control problems they are among the hardest voting rules, but for bribery and manipulation-together with k-approval voting-they often lay on the edge of (in)tractability. It is thus interesting to see their complexity for each of the problems separately.

O O B B O B I O O O B I O O O O O B I I O O O O O O O O O O O O O O O O O O O O O O B O O O O O B O O B I O O O O O O O O O O O O O O O O O O O O O O O B O B O O O O O O O O O O B I O O O O O B O B O O O O O O O O O O O O O O O O O O O O O O O O O O B B O B I O O O B I O O O O O O B I O O O O O O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O O


Outlier Modeling in Image Matching Abstract-We address the question of how to characterize the outliers that may appear when matching two views of the same scene. The match is performed by comparing the difference of the two views at a pixel level aiming at a better registration of the images. When using digital photographs as input, we notice that an outlier is often a region that has been occluded, an object that suddenly appears in one of the images, or a region that undergoes an unexpected motion. By assuming that the error in pixel intensity generated by the outlier is similar to an error generated by comparing two random regions in the scene, we can build a model for the outliers based on the content of the two views. We illustrate our model by solving a pose estimation problem: the goal is to compute the camera motion between two views. The matching is expressed as a mixture of inliers versus outliers, and defines a function to minimize for improving the pose estimation. Our model has two benefits: First, it delivers a probability for each pixel to belong to the outliers. Second, our tests show that the method is substantially more robust than traditional robust estimators (M-estimators) used in image stitching applications, with only a slightly higher computational complexity. I N image matching, a function finds corresponding pixels in two images. It enables, for example, to extract some information from the scene, to construct a 3D model, or to stitch a panorama. At some level of the computation, the matching function compares the pixel values of both images at matching positions, with the goal of iteratively refining the estimation. Even if there is a perfect geometrical match between the images, the pixel values will differ, either because of noise, or because there is something that violates the assumption made to do the match; in other words, an outlier. An outlier in an (photographic) image pair is often a region that has been occluded, an object that suddenly appears in one of the images, or a region that undergoes an unexpected motion. The fundamental problem of outlier rejection or robust estimation is to distinguish between noise, slight misregistrations, and outliers. In practice, given a difference between two pixel values, one should be able to decide whether, or to which extent, the pixel needs to be considered or discarded from the computation.. In this paper, we address this problem by extracting as much information as we can from the images prior to any matching computation. The key idea of this paper is to predict the outlier statistical characteristics as follows: We assume that, by comparing two arbitrary parts of each image, the resulting error pattern is similar to the one generated by an outlier. From this assumption, we can compute the expected error distribution generated by the outliers, which leads us to the outlier model. This model is very general and can be applied to any image matching application. The second part of this paper shows how to apply the outlier model to a particular case of image matching, namely, to camera pose estimation.. The outlier model enables us to express a pose estimation problem as a mixture of inlier versus outliers, and to handle outlier rejection like a standard mixture problem [1] , [2] . The performance of the model is demonstrated using two different types of experiments. The first experiment shows two aligned pictures, one of them containing an outlier. The proportion of the image covered by the outlier is varied by framing the images of the pair differently. The goal is to see when the model breaks down. The second experiment compares the pose estimator derived from our outlier model-which is an M-estimator-to a standard robust M-estimator.. After a brief discussion of the state-of-the-art in Section 2, the paper starts by presenting the outlier model in Section 3. In Section 4, we discuss how to apply the model to the pose estimation problem. We show two types of results. The first is how to discriminate inliers from outliers given a set of registered images. The second addresses the robustness of the pose estimation in the presence of an increasing number of outliers. In both cases, the model shows substantial improvement compared to existing techniques. Section 5 briefly discusses the limitations of the model, followed by the conclusion in Section 6. In this paper, we present a new way of calculating outliers in image pairs. The method differs from the traditional approach by characterizing the outliers with a distribution computed from the initial images. This restriction in the outlier characterization allows the description of a new motion estimator that treats the pose estimation as a mixture of inliers versus outliers and is able to handle outlier percentages that exceed 50 percent of the image. The model has been tested using two kinds of experiments: The first experiment tests the ability of the model to discriminate the outliers from the inliers using two pictures taken with a fixed camera. The second experiment tests the performance of the motion estimator derived from the During his undergraduate studies, he was an exchange student at the Carnegie Mellon University in Pittsburgh, Pennsylvania, and did his master's thesis at Daimler-Chrysler research, in Ulm, Germany, working on sensor simulation. He then joined the graduate school in Communication Systems at EPFL where he was awarded with a three year PhD fellowship. During his studies, he also worked at NASA Ames, California, on a mobile robot field test, and at Sony Research, California, on highdynamic range imaging. In early 2002, he joined a startup companyGenimedia SA-and worked on perceptual image quality metrics. His main research area is computer vision and digital photography, with emphasis on color. He is a member of the IEEE.. Luciano Sbaiz received the "Laurea in Ingegneria Elettronica" degree from the University of Padova in 1993 (score 110/110 with honors). The object of his graduation thesis was the implementation and testing of an image coder based on the wavelet transform and using an efficient prediction technique of the wavelet coefficients. In 1994, he obtained a fellowship from Seleco S.p.A., Pordenone, Italy. From 1994 to 1997, he has worked on the Doctorate degree in electronics and telecommunications in the Departimento di Elettronica e Informatica, University of Padova, with advisor Professor Gian Antonio Mian. The topic of his research concerned the application of computer vision motion estimation algorithms to object oriented and model based video coders. The algorithm that has been developed is based on a representation of the scene by means of objects that undergo rigid motion. The motion equations are arranged in the form of a dynamic system whose state, which contains the motion parameters, is estimated by means of an extended implicit Kalman filter. The parameterization of the model allows for a very efficient coding of motion information in comparison to more common block-based schemes. Moreover, the structure imposed by the model implies that the reconstructed motion is very natural. During the years from 1997 to 1999, he worked as assistant at the Laboratory of Audio Visual Communications (LCAV) of the Swiss Federal Institute of Technology (EPFL) of Lausanne. His research concerned the development of computer vision techniques with application to the creation of video special effects. Since Semptember 1999, he works with Dartfish SA, Fribourg, Switzerland. His tasks concern the development of algorithms for video processing and motion estimation. ETHZ (1990) and Stanford (1998) . He is a fellow of the IEEE, a member of SIAM, and was the area editor for speech, image, video, and signal processing of the He is a member of the Swiss Council on Science and Technology. He was a plenary speaker at various conferences (e.g., 1992 IEEE International Conference on Acoustics, Speech and Signal Processing) and is the coauthor, with J. Kovacevic, of the book Wavelets and Subband Coding, (Prentice-Hall, 1995). He has published more than 85 journal papers on a variety of topics in signal/image processing and communications and holds seven patents. His research interests include sampling, wavelets, multirate signal processing, computational complexity, signal processing for communications, digital video processing, and joint source/channel coding.. . For more information on this or any other computing topic, please visit our Digital Library at http://computer.org/publications/dlib. To illustrate the behavior of each fitting method, two pictures of a pedestrian street are shown. The outliers are the pedestrians along with their shades and the inliers are the background regions of the scene. The outlier proportion is varied by extracting from the image in Figs. 5a and 5b several subimages, which contain less and less background information, as illustrated in Figs. 5c, 5d, 5e, and 5f. Table 1 shows the result of fitting the OutlierMix model to the error histogram. The sensitive parameter is the inlier scale since the background is similar for every image pair, the inlier scale value should not change within the table. 4 The L 2 estimator differs slightly from the maximum likelihood, but gave also very satisfactory results. Although the relative differences between the estimates of the inlier scale appears to be large, its absolute value is very small compared to the dynamic range of the error ( À1; 1 ½ ). The outlier modeling is also compared to the UniformMix model, which assumes that the outliers can be represented by a uniform distribution. The results shown in Table 2 are not as good as the ones using the OutlierMix modeling, but are still better than the traditional median-based approach.. The modeling fit is shown in Fig. 10 for the OutlierMix model using the maximum likelihood estimator. The fit is only shown for the maximum-likelihood estimator because, graphically, there is hardly a difference with the L 2 estimator. Fig. 11 shows the outlier mask. The outlier mask represents, for each pixel, the probability to belong to the outliers-defined by (14) -where the gray scale is linearly related to the probability to be an outlier (black is used for high probability of outliers). We can see that the mask is able to discriminate the inliers from the outliers even in the presence of more than 95 percent outliers.

O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O


Extracting collective expectations about the future from large text collections News articles often contain information about the future. Given the huge volume of information available nowadays, an automatic way for extracting and summarizing futurerelated information is desirable. Such information will allow people to obtain a collective image of the future, to recognize possible future scenarios and be prepared for the future events. We propose a model-based clustering algorithm for detecting future events based on information extracted from a text corpus. The algorithm takes into account both textual and temporal similarity of sentences. We demonstrate that our algorithm can be used to discover future events and estimate their probabilities over time. Future-related information can be found in textual documents such as newspapers, books and Web pages. They usually contain information such as plans, speculations, predictions and expectations and constitute an excellent source of what may happen in the future. However, the huge volume of information available makes it difficult for any person to detect all important future-related information manually, not to mention obtaining a clear picture of possible future scenarios.. In view of this challenge, we propose a framework for analyzing future-related information in a text corpus. Our goal is a system that can automatically extract future-related information from a large number of text documents, group related events and topics together and estimate the probabilities of these events based on the evidence found in the documents. We consider a query such as the name of a country, an enterprise, a celebrity or a well-known topic as the input of the system. To inform the design of our framework we first perform simple analysis of selected characteristics of future-related information (Section 3.3).. Our framework helps users understand the possible future scenarios associated with the entity given in the query based on the collective image of the future constructed from large textual collections. It should be noted however that our objective is not to predict the future per se. Instead, we propose a framework that can be used to provide the current view of the future that the society collectively expresses in large text collections.. Future forecasting has always been an important activity of humans and thus there should be many potential use cases for such a framework. In particular, a collective image of the future will be useful in various decision making scenarios. To name just a few, users wishing to invest in certain companies may be interested in their future perspectives and plans; fans of celebrities may want to know the schedules related to these persons; those who are considering moving to a certain city may want to know more about the development plans of the local government.. In the next section, we review related research works. Section 3 describes our dataset and presents some statistical analysis. In Section 4 we explain in detail our proposed framework. We describe several case studies and experiments in Section 5. Finally, we discuss some important issues regarding our work in Section 6, and conclude the paper in Section 7. Given the large amount of future-related information in text documents, it is possible to harness such data to construct a collective image of the future. We proposed a modelbased framework for portraying collective images of the future, constructed based on numerous future-related information expressed in text collections. The framework supports users in understanding the currently planned or expected future events for a given query, be it a person, a company, a city or a country. We demonstrated its effectiveness on several examples of real world entities. Besides considering the additional factors mentioned in the previous section, we plan to improve our clustering algorithm and perform evaluation of larger scale in the future. Our work is related to a number of areas including information extraction, information retrieval and data mining. While a lot of work has been done to process temporal information found in documents (e.g. [1] [9]), relatively little research has been done specifically on future-related information. Baeza-Yates [2] is the first to talk about "future retrieval." He presents the idea of constructing a search engine that extracts future temporal expressions from news articles and represents documents using tuples of time segments and confidence probabilities of future events.. Jatowt et al. [4] summarizes future-related information in both Web pages and news articles. Two methods are proposed to generate summaries of future events. Firstly, information about a certain entity is agglomerated by issuing queries containing object names and future dates (e.g. 2020, 2030) to search engines. Secondly, news articles mentioning a periodical event are analyzed in order to discover its periodicity, which can be then used to predict the future occurrence of the event. This work further develops the above concepts by taking into account the uncertainty in a piece of future-related information, and by establishing a unified and model-based approach to cluster and summarize future-related information.. Kanhabua et al. [6] propose ranking model for predictions that takes into consideration their relevance. Time Explorer [8] is a search engine that lets users search in the future and analyze future evolution of topics. Kanazawa et al. [5] describe methods for retrieval and validity analysis of future-related information which is not associated with explicit future dates. Our task is different from the above works as we focus on estimating the probability of events based on the aggregated evidence of future-related expressions found in text collections. Evaluating our proposed method is a challenging task because no benchmark dataset or ground truth is available. The results contain information about events or plans that were not yet realized at the time the news articles are published. Hence, it is difficult to perform quantitative evaluation. Instead, we carry out a set of case studies in order to demonstrate the effectiveness and some characteristics of our proposed method. We select three queries, namely "Germany", "Toyota" and "NASA", representing different categories of queries.. To perform the experiments, we extract news articles from our datasets that contain temporal expressions referring to a date or a period of time in or after 2011. Due to limited space here, we only present results with number of topics |Z| = 50 and λ = 0.5, by which we obtain reasonable results. Note that the output events are generated on the basis of 20-year old (1990-2010) collection of news articles, hence they are major events that have been usually "long-awaited" and are also scheduled in relatively far future.

O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O


Numerical study of stream-function formulation governing flows in multiply-connected domains by integrated RBFs and Cartesian grids This paper describes a new numerical procedure, based on point collocation, integrated multiquadric functions and Cartesian grids, for the discretisation of the stream-function formulation for flows of a Newtonian fluid in multiply-connected domains. Three particular issues, namely (i) the derivation of the stream-function values on separate boundaries, (ii) the implementation of cross derivatives in irregular regions, and (iii) the treatment of double boundary conditions, are studied in the context of Cartesian grids and approximants based on integrated multiquadric functions in one dimension. Several test problems, i.e. steady flows between a rotating circular cylinder and a fixed square cylinder and also between eccentric cylinders maintained at different temperatures, are investigated. Results obtained are compared well with numerical data available in the literature. The motion of a Newtonian fluid is governed by the Navier-Stokes equations which can be written in terms of different dependent variables, including the velocitypressure formulation, the stream-function -vorticity formulation and the streamfunction formulation. The velocity -pressure formulation is able to work for twoand three-dimension flows in a similar manner. One main concern is that there are no explicit transport equation and boundary conditions for the pressure variable.. The resultant algebraic system could be solved iteratively where the pressure value is corrected using the continuity equation. For two-dimensional (2D) problems, by introducing the stream-function variable, one can eliminate the pressure and reduce the number of unknowns, i.e. from three (the velocity -pressure formulation) to two (stream-function and vorticity) and only one (stream-function). However, the last two formulations have some drawbacks. Special attention should be given to the handling of the vorticity boundary condition for the stream-function -vorticity formulation and the double boundary conditions as well as high-order derivatives including the cross ones for the stream-function formulation. Furthermore, the pressure field needs be computed after solving the governing equations, which is generally regarded as a complicated process. In the case of multiply-connected domains, an added difficulty is that the stream-function variable generally has different values, which are unknown, on separate boundaries. It is noted that advantages of the stream-function -vorticity formulation presented above are restricted to 2D problems.. The governing differential equations can be transformed into sets of algebraic equations by means of discretisation. To support the approximations, the problem domain needs be represented by a set of finite elements, a Cartesian grid or a collection of discrete points. For problems with complicated geometries such as flows in multiply-connected domains, it has been recognised that the task of dividing the spatial domain into a number of finite elements can be the most time-consuming part of the solution process. Generating a Cartesian grid or a set of discrete points is clearly much more economical. Over the last twenty years, radial-basis-function networks (RBFNs) have been developed to solve different types of differential problems encountered in applied mathematics, science and engineering (e.g. [1, 2, 3, 4, 5, 6, 7, 8, 9] ).. These approximators can work well with gridded and scattered points. As shown in [10, 11, 12] , there is the relation between the RBF collocation method and the finite difference method (FDM). For 1D approximations, the standard RBF interpolant converges to the Lagrange interpolating polynomial as the RBF width goes to infinity, which means that all classical FD formulas can be recovered by the limiting RBF interpolant. In the case of two and higher dimensions, the situation is not clear due to the fact that multivariate polynomial interpolations are not well-posed.. In [4, 5, 6, 7, 8] , the RBF approximations are constructed using integration (integrated RBFNs (IRBFNs)) rather than the usual differentiation. This approach has the ability to overcome the problem of reduced convergence rates caused by differentiation and to provide effective ways to implement derivative boundary values. IRBFNs have been developed for the simulation of flows in simply-connected domains governed by the stream-function formulation and the stream-function -vorticity formulation (e.g. [6] ) as well as natural convection in regions between concentric cylinders governed by the stream-function -vorticity formulation (symmetrical flows) (e.g. [4] ).. This study is concerned with the simulation of unsymmetrical flows of a Newtonian fluid in multiply-connected domains using the stream-function formulation, Cartesian grids and 1D-IRBFNs. Unlike the symmetrical case, the stream-function variable has different values on separate boundaries. These values can be found using the single-value condition for the pressure, whose implementations are known to be difficult (e.g. [13] ). Further difficulties include the implementation of cross derivatives in regions bounded by irregular surfaces as the boundary points do not generally coincide with the grid nodes. New treatments for these difficulties and their 1D-IRBF-based implementations are the focal point of this study.. An outline of the paper is as follows. The stream-function formulation and 1D-IRBFNs are briefly reviewed in Section 2 and Section 3, respectively. The proposed procedure is described in Section 4 and then numerically verified through the simulation of steady flows between a rotating circular cylinder and a fixed square cylinder and also between eccentric cylinders maintained at different temperatures in Section 5. Section 6 concludes the paper. In this article, flows in multiply-connected domains are studied using the stream-

O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O


A denial-of-service resistant intrusion detection architecture As the capabilities of intrusion detection systems (IDSs) advance, attackers may disable organizationsÕ IDSs before attempting to penetrate more valuable targets. To counter this threat, we present an IDS architecture that is resistant to denial-of-service (DOS) attacks. The architecture frustrates attackers by making IDS components invisible to attackersÕ normal means of``seeing'' in a network. Upon a successful attack, the architecture allows IDS components to relocate from attacked hosts to operational hosts thereby mitigating the attack. These capabilities are obtained by using mobile agent technology, utilizing network topology features, and by restricting the communication allowed between dierent types of IDS components. Ó While not yet seen in the wild, intrusion detection systems (IDSs) may become a primary target for attackers. As IDSs become more widely deployed, and as their automated response capability increases, attackers may ®nd it necessary to disable an organizationÕs IDS before carrying out their nefarious activity. Furthermore, such attacks may be easy to launch against the new breed of distributed IDSs with hierarchical, interdependent components. In such systems, IDSs often have command and control or analysis components that, if disabled, render the IDS useless over a large portion of the protected network. We call these critical components and the hosts on which they reside critical hosts.. To counter the threat of attackers ®nding and disabling critical IDS components, IDS vendors devote many resources towards designing IDS such that they cannot be penetrated. For the most part, these eorts have been successful and standalone intrusion detection hosts have shown a strong resistance to penetration attacks. Less eort has been spent securing IDSs from¯ooding denialof-service (DOS) attacks. In part, this is because it is widely thought that nothing can be done about this type of attack.. However, it is a common misconception that systems in general cannot avoid the consequences of a¯ooding DOS attack. To demonstrate this, our paper describes an IDS architecture that enables IDSs to become resistant to¯ooding DOS attacks. Furthermore, the model does not require IDSs to operate in an ineective or obscure manner, but rather builds upon the traditional distributed hierarchical model used by the majority of IDSs today.. Computer Networks 34 (2000) 641±658 www.elsevier.com/locate/comnet Our IDS architecture resists¯ooding DOS attacks using a combination of techniques. First, critical IDS components are made invisible to an attackerÕs normal means of seeing in a network: active network scanning and passive packet monitoring. Second, critical IDS components are made adaptive to¯ooding DOS attacks in that they can automatically relocate to another host in the event of an attack. The relocation is invisible to the attacker who then cannot persist in the attack. Our model does not prevent an attacker from launching attacks but instead makes the important targets invisible which forces the attacker to ®re blindly. Random attacks may actually hit a critical IDS host, but the ability of IDS components to move between hosts in the event of an attack mitigates the damage. The area of creating IDSs that are resistant tō ooding DOS attacks is neither well researched nor understood. Many believe that nothing can be done to prevent¯ooding DOS attacks and so they do not expend resources investigating this area. However, our model is a counter-example to this argument and proves that at least one eective method exists for designing distributed IDSs that are resistant to¯ooding DOS attacks.. Our model resists¯ooding DOS attacks using a passive response system. Instead of actively trying to stop an attacker's actions, our IDS model attempts to hide IDS components and move them away from harm. Thus, our IDS components become invisible to an attackerÕs normal means of seeing in a network: passive sning, active network monitoring, and host penetration and analysis. IDS components become invisible by using assumptions about the network topology and by restricting the communication allowed between certain types of components. In the event that a critical component is attacked, then the component moves to an operational host. While it may appear impossible for an agent to move from an attacked host, we use mobile agent technology to enable a type of backup system for processes. Thus, the agents on attacked hosts can become disabled and mobile agents on other hosts will automatically pick up the disabled componentÕs duties.. The passive nature of this solution gives our model several advantages. Unlike other existing solutions, to implement this defensive technique, one does not have to control all the routers in an organization or to degrade the ecacy of those routers for the sake of security. There is no concept of responding to an attack other than to evade or hide components, which means that there is no concern that the IDS could launch responses that might harm legitimate network trac. Also, since our model prevents attacks by making IDS components invisible, there is no issue of how quickly our IDS can respond to and mitigate an attack against itself.. Despite these advantages and other provable characteristics, our model is not a silver bullet solution as revealed by the weaknesses described in Section 18. More research needs to be done to explore dierent passive resistance models and to compare them with the active resistance models presented in Section 6.. In conclusion, we envision IDSs of the future playing an increasingly prominent role in securing organizationsÕ networks, both from the detection and response arena. Due to this, attackers will attempt to disable IDSs before penetrating more valuable resources. We see¯ooding DOS attacks as the primary threat, since future IDS back end systems are likely to be highly resistant to penetration attacks. Therefore, researchers need to explore and compare system models for resisting these attacks and vendors need to implement them beforē ooding DOS attacks become a serious problem.

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Lattice rule algorithms for multivariate approximation in the average case setting We study multivariate approximation for continuous functions in the average case setting. The space of d variate continuous functions is equipped with the zero mean Gaussian measure whose covariance function is the reproducing kernel of a weighted Korobov space with the smoothness parameter α > 1 and weights γ d,j for j = 1, 2, . . . , d. The weight γ d,j moderates the behavior of functions with respect to the jth variable, and small γ d,j means that functions depend weakly on the jth variable. We study lattice rule algorithms which approximate the Fourier coefficients of a function based on function values at lattice sample points. The generating vector for these lattice points is constructed by the component-by-component algorithm, and it is tailored for the approximation problem.Our main interest is when d is large, and we study tractability and strong tractability of multivariate approximation. That is, we want to reduce the initial average case error by a factor ε by using a polynomial number of function values in ε −1 and d in the case of tractability, and only polynomial in ε −1 in the case of strong tractability. Necessary and sufficient conditions on tractability and strong tractability are obtained by applying known general tractability results for the class of arbitrary linear functionals and for the class of function values. Strong tractability holds for the two classes in the average case setting iff sup d≥1 We provide a construction in this paper and prove tractability and strong tractability error bounds for lattice rule algorithms. This paper can be viewed as a continuation of our previous paper where we studied multivariate approximation for weighted Korobov spaces in the worst case setting. Many technical results from that paper are also useful for the average case setting. The exponents of ε −1 and d corresponding to our error bounds are not sharp. However, for α close to 1 and for slow decaying weights, we obtain almost the minimal exponent of ε −1 . We also compare the results from the worst case and the average case settings in weighted Korobov spaces. We are interested in approximating real-valued continuous functions defined on the cube [0, 1] d . The number of variables is d, and d = 1, 2, . . . . Our main interest is when d is large, even in the hundreds or thousands, as is the case for many applications in mathematical finance, quantum physics and chemistry, see [16] .. We assume that the space of continuous functions is equipped with a zero mean Gaussian measure µ d whose covariance function is the reproducing kernel of a weighted Korobov space with the smoothness parameter α > 1. In particular, the µ d -measure of the classical Korobov space with smoothness parameter β is 1 as long as β < α − 1, see Section 7. Hence, with probability 1, all functions have partial derivatives up to the order (α−1)/2 with respect to each variable.. The reproducing kernel depends on the non-negative weights γ d,j for j = 1, 2, . . . , d. The classical Korobov space corresponds to γ d,j = 1 in which case all variables play the same role. As long as d is relatively small, this is a reasonable assumption. If, however, d is large, the role of successive variables or groups of variables may be quite different. This corresponds to more general weights. In this paper we study the so-called product weights, leaving the case of general weights for future research. For product weights, we have 1. , and each weight γ d,j moderates the behavior of functions with respect to the jth variable. Small γ d,j means that functions depend weakly on the jth variable, and the limiting case when γ d,j = 0 means that functions are constant with respect to the jth variable.. In this paper we study lattice rule algorithms. Lattice rules are traditionally used for multivariate integration, see [10] . Recently there has been a significant progress in the efficient construction of generating vectors of lattice rules for multivariate integration. The generating vectors can be constructed by the component-by-component algorithm, which works for arbitrarily large d, see [3, [11] [12] [13] . The essence of this algorithm is that each component of the generating vector is computed by a one-dimensional search, with all the previous components kept unchanged. The cost of constructing an n-point lattice rule for d variables is proportional to d n log n, see [8] .. Lattice rules may also be used for multivariate approximation, see [4] and papers cited there. This paper can be viewed as a continuation of [4] . We study lattice rule algorithms which approximate the Fourier coefficients of functions based on function values at lattice sample points. The generating vector for these lattice points is constructed by the component-by-component algorithm, and is especially suited for multivariate approximation. The paper [4] considered the approximation problem in the worst case setting for functions from weighted Korobov spaces, while here we study the problem in the average case setting for a much larger class of functions -the space of continuous functions equipped with a zero mean Gaussian measure. Due to the assumption that the covariance function of the Gaussian measure is the reproducing kernel of the weighted Korobov space, many technical results from [4] can be applied to the average case analysis.. The second major theme of this paper is tractability and strong tractability of multivariate approximation in the average case setting. Tractability has recently become a popular research subject in information-based complexity, see [7] and papers cited there. The essence of this study is to find necessary and sufficient conditions for which the minimal number of information evaluations needed to reduce the initial error by a factor ε is polynomial in ε −1 and d in the case of tractability, and only polynomial in ε −1 in the case of strong tractability. When these conditions hold we want to find algorithms enjoying tractability or strong tractability error bounds.. Two classes of information evaluations are typically studied. The first class Λ all consists of all continuous functionals, whereas the second class Λ std consists of only function values. The initial error is defined as the smallest error which can be achieved without sampling the functions. Tractability and strong tractability can be studied in various settings including the worst case and the average case settings. Most papers on tractability have been devoted to the worst case setting. The average case setting has been studied in [2] , where only strong tractability is addressed, and in [1] , where both strong tractability and tractability are addressed. Necessary and sufficient conditions on tractability and strong tractability are typically expressed in terms of weights of the underlying problem. Classical spaces correspond to equal weights, γ d,j = 1, and in this case tractability does not hold, and, even worse, the minimal number of information evaluations depends exponentially on d. This is referred to as the curse of dimensionality.. Tractability can usually be obtained for sufficiently decaying weights. For multivariate approximation in the average case setting, necessary and sufficient conditions on tractability and strong tractability can be obtained from [1, 2] . , there is a trade-off between the exponents a and p. Indeed, let τ ∈ (max(1/α, t γ ), 1), where t γ is the infimum of the positive numbers t for which (2) holds. Then the exponents a and p can be equal to (for the class Λ Now let τ go to max(1/α, t γ ). Then the exponent p is minimized and goes to. but the exponent a goes to infinity when 1/α ≥ t γ or when 1/α < t γ and R τ goes to infinity. Obviously for given d and ε we should choose τ such that d. is minimized. We stress that in the case of tractability, the minimal exponent p can be arbitrarily large if α or t γ is close to 1.. The results for the class Λ all are constructive, whereas the proof presented in [2] for the class Λ std uses a non-constructive argument and therefore the results are non-constructive. We provide a construction for the class Λ std in this paper. This construction is based on lattice rule algorithms. We prove that the average case errors of lattice rule algorithms achieve tractability or strong tractability error bounds. We have the following results.. For lattice rule algorithms with the generating vector especially constructed for multivariate approximation in the average case setting, we prove in Theorem 10 that the number of function values required to reduce the average case error from its initial value by a factor of ε is of order. in the case of strong tractability,. in the case of tractability, with the factors in the big O notation independent of ε and d but dependent on p, and on a and p, respectively. Here p can be, as before, arbitrarily close to p * or p * * , depending on whether strong tractability or tractability holds, and there is a trade-off between p and a, see the second part of Theorem 10.. Clearly these bounds are not optimal. As already mentioned p can be very large when α, s γ or t γ is close to 1. In this case, the extra term 2p/(2 + p), which is always less than 2, is insignificant since p + 2p/(2 + p). On the other hand, p is small for large α and small s γ and t γ . In this case, the extra term is more important but does not cause serious concern since p + 2p/(2 + p) = p[1 + 2/(2 + p)] ≤ 2p. In other words, for a hard problem we have essentially the (already large) minimal exponent of ε −1 . When a problem is easy we are at worst doubling the (small) minimal exponent of ε. As a comparison we also consider the generating vector constructed for multivariate integration. We prove in Theorem 14 that the number of function values required is of order. in the case of strong tractability,. in the case of tractability, with the factors in the big O notation independent of ε and d but dependent on p, and on a and p, respectively. Here p can be arbitrarily close to p * or p * * , depending on whether strong tractability or tractability holds, and again there is a trade-off between p and a, see the second part of Theorem 14. The essence of these estimates is that we roughly double the exponent of ε −1 as compared to the minimal one. Thus not surprisingly the generating vector constructed especially for approximation is better than the vector constructed for integration.. In Section 7 we compare the worst case and the average case settings for multivariate approximation defined over weighted Korobov spaces. We show how much easier the average case setting is, and show that much smaller tractability and strong tractability exponents can be obtained in the average case setting, compared to the worst case setting. Finally in Section 8 we discuss the implementation issues associated with the construction of generating vectors and present numerical results.

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