ppxscal/embedding_network huggingface dataset:
Multistage Lot Sizing Problems via Randomized Rounding
Authors: Chung-Piaw Teo, Dimitris Bertsimas
Venue: Operations Research (2001)

We study the classical multistage lot sizing problem that arises in distribution and inventory systems. A celebrated result in this area is the 94% and 98% approximation guarantee provided by power-of-two policies. In this paper, we propose a simple randomized rounding algorithm to establish these performance bounds. We use this new technique to extend several results for the capacitated lot sizing problems to the case with submodular ordering cost. For the joint replenishment problem under a fixed base period model, we construct a 95.8% approximation algorithm to the (possibly dynamic) optimal lot sizing policy. The policies constructed are stationary but not necessarily of the power-of-two type. This shows that for the fixed based planning model, the class of stationary policies is within 95.8% of the optimum, improving on the previously best known 94% approximation guarantee.
Lessons learned becoming a framework developer
Authors: James Carey, Brent Carlson
Venue: Software&mdash;Practice Experience (2002)

When we began developing frameworks we were naive about what was involved in developing a framework versus other software. We had experience in object-oriented development, but even that did not prepare us for some of what we learned as we developed frameworks. This paper captures some of the lessons that we learned as we became framework developers. If you have already developed frameworks these will validate what you have already learned, but for someone just starting out these are the areas where we believe you will be surprised. For example, are you ready to become comfortable exposing your work completely, since almost everything might be part of the framework product? Are you ready to become more disciplined so you can manage and deliver all these pieces? Other lessons will validate and enhance what you learned developing object-oriented software; for example, the value of patterns, especially to define customization points. All are part of the biggest lesson of all, that as a framework developer you are no longer independently developing an application for an end-user, instead you are on the many diverse customer teams using the framework--helping them deliver their applications.
Error estimates for a single phase quasilinear Stefan problem with a forcing term
Authors: Mi Ray Ohm, Jun Yong Shin, Hyun Young Lee
Venue: The Korean Journal of Computational Applied Mathematics (2003)

In this paper, we apply finite element Galerkin method to a single-phase quasi-linear Stefan problem with a forcing term. We consider the existence and uniqueness of a semidiscrete approximation and optimal error estimates in L2, L∞, H1 and H2 norms for semidiscrete Galerkin approximations are derived.
The Four-Day Aircraft Maintenance Routing Problem
Authors: Graeme S. Pauley, Richard J. Ormerod, Robert E. D. Woolsey, Kalyan T. Talluri
Venue: Transportation Science (1998)

Federal aviation regulations require that all aircraft undergo maintenance after flying a certain number of hours. Most major U.S. airlines observe the maintenance regulations by requiring that aircraft spend a night at a maintenance station after at most three or four days of flying. In addition, some airlines require that every aircraft goes through a special maintenance station for what is commonly called a balance check. Airlines usually schedule routine maintenance only at night so as not to cut into aircraft utilization. The maintenance routing problem is to find a routing of the aircraft that satisfies the short-term routine maintenance requirements. In Gopalan, R. and Talluri, K. T. ("The Aircraft Maintenance Routing Problem," Opns. Res. in press) we modeled this problem as one of generating an appropriate directed graph (called a line-of-flight-graph), and of finding a special Euler Tour called the k-day Maintenance Euler Tour (k-MET, for k = 3, 4,...) in that directed graph-for finding a maintenance routing in which the aircraft would spend at most k days of flying before overnighting at a maintenance station and have an opportunity for a balance-check. In the same paper we gave a polynomial-time algorithm for finding a 3-MET, if one exists, in the directed graph. In this paper we consider the routing problem when the requirement is to overnight at a maintenance station after at most four days of flying and to undergo the balance check every n days, where n is the number of planes in the fleet of the equipment type under consideration. We show that this problem is NP-complete; in fact, that the k-MET problem is NP-complete for all k &#8805; 4. When the number of maintenance stations is exactly one, we show that the 4-MET problem can be solved by solving an appropriate bipartite matching problem; and hence in polynomial time. As a corollary to this result, we show that when there is no balance check station visit requirement, the four-day routing problem, in a given LOF-graph, can be solved (without any restrictions on the number of maintenance stations) in polynomial time. We show how our polynomial-time algorithms for the 3-MET problem and the restricted 4-MET problem can be used to design effective heuristics for the 4-MET problem.
Privacy through pseudonymity in user-adaptive systems
Authors: Alfred Kobsa, Jörg Schreck
Venue: ACM Transactions on Internet Technology (TOIT) (2003)

User-adaptive applications cater to the needs of each individual computer user, taking for example users' interests, level of expertise, preferences, perceptual and motoric abilities, and the usage environment into account. Central user modeling servers collect and process the information about users that different user-adaptive systems require to personalize their user interaction.Adaptive systems are generally better able to cater to users the more data their user modeling systems collect and process about them. They therefore gather as much data as possible and "lay them in stock" for possible future usage. Moreover, data collection usually takes place without users' initiative and sometimes even without their awareness, in order not to cause distraction. Both is in conflict with users' privacy concerns that became manifest in numerous recent consumer polls, and with data protection laws and guidelines that call for parsimony, purpose-orientation, and user notification or user consent when personal data are collected and processed.This article discusses security requirements to guarantee privacy in user-adaptive systems and explores ways to keep users anonymous while fully preserving personalized interaction with them. User anonymization in personalized systems goes beyond current models in that not only users must remain anonymous, but also the user modeling system that maintains their personal data. Moreover, users' trust in anonymity can be expected to lead to more extensive and frank interaction, hence to more and better data about the user, and thus to better personalization. A reference model for pseudonymous and secure user modeling is presented that meets many of the proposed requirements.
FE analysis of large deformations of membranes with wrinkling
Authors: M. Stanuszek
Venue: Finite Elements in Analysis and Design (2003)

The numerical analysis of large deformations of flexible membrane structures is considered in this paper. Taking advantage of the natural approach (Comput. Methods Appl. Mech. Eng. 6 (1978) 369.) applied to the tension systems, complex membrane structures of arbitrary shape with wrinkling allowed are analysed. In the study, the Finite Element Method with triangular membrane elements is used. The geometrical nonlinearity as a result of large displacements, shape dependent loads (e.g. internal pressure) and unilateral static boundary conditions add considerable complexity to the analysis of such objects. In the case of wrinkling a new concept of taking wrinkles into account based on the cable analogy is proposed. The Newton-Raphson technique is used to solve the nonlinear equilibrium equations of the system and special attention is paid the assessment of the convergence of the iteration process. A professional computer code, Nonlinear Analysis by Finite Difference and Element Methods (NAFDEM), was developed and applied to solve numerous practical examples of large deformations of complex membrane structures with wrinkling.
Electronic Mail and Organizational Communication: Does Saying "Hi" Really Matter?
Authors: Marjorie Sarbaugh-Thompson, Martha Feldman
Venue: Organization Science (1998)

When people use electronic mail, they can communicate even when they are not physically or temporally proximate. Thus, it is not surprising that most studies report that the use of electronic mail increases organizational communication. In the study presented here, overall organizational communication declined as use of electronic mail increased. As we probed the nature of this decline, we discovered that much of the lost communication was greetings. This raises questions about the role that greetings, and other forms of casual conversation, play in an organization. To organize our insights about this topic we formulate a two-by-two communication matrix based on presence versus absence and availability versus unavailability. Prior research focuses on the ways being present and available and being absent but available through electronic mail affect the performance of specific communication tasks. Using our typology, we direct attention to the role of casual conversation in presence availability and to the parts that presence unavailability and absence unavailability can play in organizational communication.
Efficient Query Execution Techniques in a 4DIS Video Database System for eLearning
Authors: Chi-Wai Fung, Elvis Wai-Chung Leung, Qing Li
Venue: Multimedia Tools and Applications (2003)

In this paper, we describe our work on developing an eLearning video database system. The eLearning video database provides a temporal modeling framework for describing eLearning video data and it supports data distribution by applying vertical class partitioning techniques. Building on top of our previous work on Four Dimensional Information System (4DIS)&mdash;an object-oriented temporal modeling framework, we apply vertical class partitioning techniques onto a 4DIS eLearning video database system as a means for efficient query execution. We further describe our work on dynamic fetching of multimedia eLearning video on the Internet. A detailed cost model for query execution through vertical class partitioning is developed. Finally, we demonstrate through the use of a running example the effectiveness of our vertical class partitioning approach.
Subthreshold leakage modeling and reduction techniques
Authors: James Kao, Siva Narendra, Anantha Chandrakasan
Venue: Proceedings of the 2002 IEEE/ACM international conference on Computer-aided design (2002)

As technology scales, subthreshold leakage currents grow exponentially and become an increasingly large component of total power dissipation. CAD tools to help model and manage subthreshold leakage currents will be needed for developing ultra low power and high performance integrated circuits. This paper gives an overview of current research to control leakage currents, with an emphasis on areas where CAD improvements will be needed. The first part of the paper explores techniques to model subthreshold leakage currents at the device, circuit, and system levels. Next, circuit techniques such as source biasing, dual Vt partitioning, MTCMOS, and VTCMOS are described. These techniques reduce leakage currents during standby states and minimize power consumption. This paper also explores ways to reduce total active power by limiting leakage currents and optimally trading off between dynamic and leakage power components.
Valuation of R and D Projects Using Options Pricing and Decision Analysis Models
Authors: Robert K. Perdue, William J. McAllister, Peter V. King, Bruce G. Berkey
Venue: Interfaces (1999)

A combination of options-pricing techniques and decision-analysis tools forms a practical process for evaluating R and D projects in a way that correctly values the impact of decision flexibility and the inevitable technical and commercial uncertainties. The options perspective leads to research-funding and project-selection decisions that can be radically different from those developed using the standard net-present-value financial rule. Decision-analysis tools simplify data acquisition. We applied the process at the Westinghouse Science and Technology Center using 13 embryonic research projects as a pilot test and subsequently applied it to the center's complete portfolio of research projects. Such an approach can be cost-effective for the type of scaled-down and decentralized research efforts that increasingly characterize US industry and can help research managers to optimize the level and composition of their research portfolios.
Analysis of Lagrangian Lower Bounds for a Graph Partitioning Problem
Authors: Gajendra K. Adil, Jay B. Ghosh
Venue: Operations Research (1999)

Recently, Ahmadi and Tang (1991) demonstrated how various manufacturing problems can be modeled and solved as graph partitioning problems. They use Lagrangian relaxation of two different mixed integer programming formulations to obtain both heuristic solutions and lower bounds on optimal solution values. In this note, we point to certain inconsistencies in the reported results. Among other things, we show analytically that the first bound proposed is trivial (i.e., it can never have a value greater than zero) while the second is also trivial for certain sparse graphs. We also present limited empirical results on the behavior of this second bound as a function of graph density.
From the Editor in Chief: Do You Know How to Get to Carnegie Hall?
Authors: Robert E. Filman
Venue: IEEE Internet Computing (2003)

Service abstraction is a wonderful concept, but it provides only a painfully limiting interaction quality. Someday, we might include in our software curriculum the principle that the foundation of intermodule communications is context-based conversation.
Parallelism and Images: A Parallelization Experiment for Image Segmentation with an Application for Automatic Classification of Scenes Obtained from Orbital Platforms
Authors: Silene De Freitas Fernandes, Antônio Miguel Vieira Monteiro, Celso Luiz Mendes
Venue: Proceedings of the 13th Brazilian Symposium on Computer Graphics and Image Processing (2000)

Segmentation is an important step in image analysis for remote sensing; it is responsible for splitting the image into distinct parts. Current segmentation methods used in images of this type are usually based on an analysis of the pixel values in all image bands. This type of analysis can be computationally expensive. In order to reduce the processing time in the image segmentation process, this paper introduces a parallel approach to image segmentation. This method is based on a region-growing technique. The parallelism is done using the SPMD (single process, multiple data) paradigm and the message-passing model under MPI (Message Passing Interface). The results have been compared with the output of a sequential system executing in the same environment.
On the nonexistence of a Lobachevsky geometry model of an isotropic and homogeneous universe
Authors: Michal Křížek, Jana Pradlová
Venue: Mathematics and Computers in Simulation (2003)

According to the Einstein cosmological principle, our universe is homogeneous and isotropic, i.e. its curvature is constant at any point and in any direction. On large scales, when all local irregularities are ignored, this assumption has been confirmed by astronomers. We show that there is no reasonable hyperbolic geometry model in R4 of a homogeneous and isotropic universe for a fixed time which would fit the cosmological principle. Hence, there does not exist any model in R4 of an isotropic universe which would be represented by a three-dimensional hypersurface with the Lobachevsky geometry.
Stochastic Network Interdiction
Authors: Kelly J. Cormican, David P. Morton, R. Kevin Wood
Venue: Operations Research (1998)

Using limited assets, an interdictor attempts to destroy parts of a capacitated network through which an adversary will subsequently maximize flow. We formulate and solve a stochastic version of the interdictor's problem: Minimize the expected maximum flow through the network when interdiction successes are binary random variables. Extensions are made to handle uncertain arc capacities and other realistic variations. These two-stage stochastic integer programs have applications to interdicting illegal drugs and to reducing the effectiveness of a military force moving materiel, troops, information, etc., through a network in wartime. Two equivalent model formulations allow Jensen's inequality to be used to compute both lower and upper bounds on the objective, and these bounds are improved within a sequential approximation algorithm. Successful computational results are reported on networks with over 100 nodes, 80 interdictable arcs, and 180 total arcs.
Neural Networks for Combinatorial Optimization: a Review of More Than a Decade of Research
Authors: Kate A. Smith
Venue: INFORMS Journal on Computing (1999)

It has been over a decade since neural networks were first applied to solve combinatorial optimization problems. During this period, enthusiasm has been erratic as new approaches are developed and (sometimes years later) their limitations are realized. This article briefly summarizes the work that has been done and presents the current standing of neural networks for combinatorial optimization by considering each of the major classes of combinatorial optimization problems. Areas which have not yet been studied are identified for future research.
Integrating User Preferences and Real-Time Workload in Information Services
Authors: Prabhudev Konana, Alok Gupta, Andrew B. Whinston
Venue: Information Systems Research (2000)

We propose priority pricing as an on-line adaptive resource scheduling mechanism to manage real-time databases within organizations. These databases provide timely information for delay sensitive users. The proposed approach allows diverse users to optimize their own objectives while collectively maximizing organizational benefits. We rely on economic principles to derive priority prices by modeling the fixed-capacity real-time database environment as an economic system. Each priority is associated with a price and a delay, and the price is the premium (congestion toll resulting from negative externalities) for accessing the database. At optimality, the prices are equal to the aggregate delay cost imposed on all other users of the database. These priority prices are used to control admission and to schedule user jobs in the database system. The database monitors the arrival processes and the state of the system, and incrementally adjusts the prices to regulate the flow. Because our model ignores the operational intricacies of the real-time databases (e.g., intermediate queues at the CPU and disks, memory size, etc.) to maintain analytical tractability, we evaluate the performance of our pricing approach through simulation. We evaluate the database performance using both the traditional real-time database performance metrics (e.g., the number of jobs serviced on time, average tardiness) and the economic benefits (e.g., benefits to the organization). The simulation results, under various database workload parameters, show that our priority pricing mechanism not only maximizes organizational benefits but also outperforms in all aspects of traditional performance measures compared to frequently used database scheduling techniques, such as first-come-first-served, earliest deadline first and least slack first.
Effective Sequencing Rules for Closed Manufacturing Networks
Authors: Wendell G. Gilland
Venue: Operations Research (2001)

This paper develops a method for determining sequencing policies to effectively control a multistation closed queueing network. We assume that several job classes, with different service time distributions, share each server and should be sequenced to maximize the long-run throughput rate of the system. A Brownian control problem that approximates the original queueing network is formulated and used to develop a dynamic sequencing policy that seeks to prevent idleness, unless the system is at a face of theworkload imbalance polytope that arises in the Brownian formulation. Several examples are used to demonstrate the benefit of this policy over the static prioritization proposed by Chevalier and Wein (1993), which has previously been shown to dominate traditional scheduling policies in a closed network setting.
Methods for distributed unicast in hypercubes
Authors: Hossam M. A. Fahmy, Abu_Bakr A. ElHefnawy
Venue: Journal of Systems Architecture: the EUROMICRO Journal (2003)

Unicast algorithms in off-line routing have been used for one-to-one communication between a source node and a destination node in an n-dimensional hypercube, denoted as Hn. A node is called k-safe, where 0 ≤ k ≤ n, if it has at least k healthy neighbors, and Hn is called k-safe if every node in it is k-safe. A k-safe Hn is connected if the number of faulty nodes, |F|, does not exceed 2k(n - k) - 1. In this paper, we propose two methods for distributed routing. The first method has been presented in [Proc. 7th Int. IEEE Conf. Electron., Circ. Syst., Jounieh, Lebanon, December, 2000, p. 194]. The second method that has not been addressed before, can be used for off-line routing. In the case of off-line routing we avoid the cost of collecting global information about the faulty nodes, and the cost of getting information about Hn, whether it is k-safe or not. The minimum requirements of the proposed methods is to have the path between the source and the destination connected. Hence, they may work when Hn is disconnected, which is an important advantage. The time cost of the first method may be O(mn4), and the expected length of the routing path between source and destination may be O(mn5), where 1 ≤ m ≤ n. The time cost of the second method may be O(enn/2), the space cost may be O(enn/2), and the expected length of the routing path between source and destination may be d(s, t).
A root graph that is locally the line graph of the Petersen graph
Authors: A. E. Brouwer, J. H. Koolen, M. H. Klin
Venue: Discrete Mathematics (2003)

We construct a root graph on 192 vertices that is locally the line graph of the Petersen graph, a new distance-regular graph on 96 vertices (with intersection array {15, 10, 1; 1, 2, 15} and automorphism group 24.Sym(6)), and several new strongly regular graphs (with parameters (υ, k, λ, µ) = (96, 20, 4, 4) and (96, 19, 2, 4)) and square 2-(96, 20, 4) designs.
On a new method to T-transitive fuzzy relations
Authors: Luis Garmendia, Adela Salvador
Venue: Technologies for constructing intelligent systems: tools (2002)

This paper provides a new method to construct a T-transitive fuzzy relation that is contained in the initial fuzzy relation.
Positivity preserving finite element approximation
Authors: Ricardo H. Nochetto, Lars B. Wahlbin
Venue: Mathematics of Computation (2002)

We consider finite element, operators defined on "rough" functions in a bounded polyhedron Ω in RN. Insisting on preserving positivity in the approximations, we discover an intriguing and basic difference between approximating functions which vanish on the boundary of Ω and approximating general functions which do not. We give impossibility results for approximation of general functions to more than first order accuracy at extreme points of Ω. We also give impossibility results about invariance of positive operators on finite element functions. This is in striking contrast to the well-studied case without positivity.