Procedia Computer Science

Simulation-based optimization combines simulation experiments used to evaluate the objective and/or constraint functions with an optimization algorithm. Compared with classical optimization, simulation based optimization brings its specific problems and restrictions. These are discussed in the paper. Evaluation of the objective function is based on time consuming, typically repeated simulation experiments. So we believe that the main objective in selecting the optimization algorithm is minimization of the number of objective function evaluations. In this paper we concentrate on integer optimization that is typical in simulation context. Local search algorithms that try to minimize the number of objective function evaluations are described. Examples with both analytical and simulation-based objective functions are used to demonstrate the performance of the algorithms.peer-reviewe

Simulating Population Protocols in Sub-Constant Time per Interaction

We consider the efficient simulation of population protocols. In the population model, we are given a system of n agents modeled as identical finite-state machines. In each step, two agents are selected uniformly at random to interact by updating their states according to a common transition function. We empirically and analytically analyze two classes of simulators for this model. First, we consider sequential simulators executing one interaction after the other. Key to the performance of these simulators is the data structure storing the agents\u27 states. For our analysis, we consider plain arrays, binary search trees, and a novel Dynamic Alias Table data structure. Secondly, we consider batch processing to efficiently update the states of multiple independent agents in one step. For many protocols considered in literature, our simulator requires amortized sub-constant time per interaction and is fast in practice: given a fixed time budget, the implementation of our batched simulator is able to simulate population protocols several orders of magnitude larger compared to the sequential competitors, and can carry out 2^50 interactions among the same number of agents in less than 400s

Transient responses of dynamical systems with random uncertainties

International audienceA new approach is presented for modeling random uncertainties by a nonparametric model allowing transient responses of mechanical systems submitted to impulsive loads to be predicted in the context of linear structural dynamics. The probability model is deduced from the use of the entropy optimization principle whose available information involves the algebraic properties related to the generalized mass, damping and stiffness matrices which have to be positive-definite symmetric matrices, and the knowledge of these matrices for the mean reduced matrix model. An explicit construction and representation of the probability model have been obtained and are very well suited to algebraic calculus and to Monte Carlo numerical simulation in order to compute the transient responses of structures submitted to impulsive loads. Finally, a simple example is presented

The role and use of sketchpad as a modeling tool in secondary schools.

Thesis (Ph.D.)-University of Durban-Westville, 2004.Over the last decade or two, there has been a discernible move to include modeling in the mathematics curricula in schools. This has come as the result of the demand that society is making on educational institutions to provide workers that are capable of relating theoretical knowledge to that of the real world. Successful industries are those that are able to effectively overcome the complexities of real world problems they encounter on a daily basis. This research study focused, to some extent, on the different definitions of modeling and some of the processes involved. Various examples are given to illustrate some of the methods employed in the process of modeling. More importantly, this work attempted to build on existing research and tested some of these ideas in a teaching environment. This was done in order to investigate the feasibility of introducing mathematical concepts within the context of dynamic geometry. Learners, who had not been introduced to specific concepts, such as concurrency, equidistant, and so on, were interviewed using Sketchpad and their responses were analyzed. The research focused on a few aspects. It attempted to determine whether learners were able to use modeling to solve a given real world problem. It also attempted to establish whether learners developed a better understanding when using Sketchpad. Several useful implications have evolved from this work that may influence both the teaching and learning of geometry in school. Initially these learners showed that, to a large extent, they could not relate mathematics to the real world and vice versa. But a pertinent finding of this research showed that, with guidance, these learners could apply themselves creatively. Furthermore it reaffirmed the idea that learners can be taught from the general to the more specific, enabling them to develop a better understanding of concepts being taught. Perhaps the findings and suggestions may be useful to pre-service and in-service educators, as well as curriculum developers

Simulation of automated negotiation

Durch die Automatisierung von Verhandlungen sollen bessere Verhandlungsergebnisse erzielt werden können als bei Verhandlungen zwischen Menschen und neue Koordinationsformen für autonome Agentensysteme ermöglicht werden. Diese Arbeit beschäftigt sich mit der Simulation solcher Systeme für automatisierte Verhandlungen, da operative Systeme zur Zeit noch nicht verfügbar sind. Die Arbeit basiert auf einer Erhebung und Diskussion der aktuellen Literatur im Bereich der Simulation automatisierter Verhandlungen. Existierende Ansätze weisen einige Unzulänglichkeiten bezüglich deren praktischer Umsetzbarkeit in einer offenen Umgebung wie dem Internet auf, wo automatisierte Verhandlungen nicht nur sehr schnell durchgeführt werden sondern sich auch Software-Agenten und Verhandlungsprobleme ändern können. Diese Defizite thematisierend werden Verhandlungssysteme für automatisierte Verhandlungen vorgeschlagen. Diese bestehen zum einen aus Software-Agenten, die generische Angebots- und Konzessionsstratgien verfolgen, zum anderen aus Interaktionsprotokollen, die es Agenten erlauben ihre Strategien vorübergehend oder permanent auszusetzen. Ergebnisse der Simulation dieser Systeme, mit Verhandlungsproblemen aus Verhandlungsexperimenten mit menschlichen Probanden als Input, werden für unterschiedliche Ergebnisdimensionen -- Übereinkunftshäufigkeit, Fairness, individuelle und kollektive Effizienz -- zwischen Systemen und auch mit den Ergebnissen der Experimente verglichen. Trotz fundamentaler Zielkonflikte zwischen den einzelnen Ergebnisdimensionen erzielen einige Systeme konsistent bessere Ergebnisse sowohl im Systemvergleich als auch verglichen mit den Ergebnissen der Experimente. Diese Systeme bestehen aus Software-Agenten die systematisch Angebote mit monoton abnehmendem Nutzen unterbreiten und erste Konzessionensschritte tätigen solange der Opponent bisherige Konzessionen erwidert hat. Das verwendete Interaktionsprotokoll zeichnet sich dadurch aus, dass es den Agenten erlaubt ungünstige Angebote zurückzuweisen und damit neue Angebote des Opponenten einzufordern, durch diese Unterbrechung der eigenen Angebotsstrategie können ungünstige Verhandlungsergebnisse vermieden werden.Automated negotiation is argued to improve negotiation outcomes by replacing humans and to enable coordination in autonomous systems. As operative systems do not yet exist scholars rely on simulations to evaluate potential systems for automated negotiation. This dissertation reviews the state of the art literature on simulation of automated negotiation along its main components - negotiation problem, interaction protocol, and software agents. Deficiencies of existing approaches concerning the practical application in an open environment as the Internet - where automated negotiation proceeds fast, with changing opponents, and for various negotiation problems - are identified. To address these deficiencies we develop and simulate automated negotiation systems, consisting of software agents that follow generic offer generation and concession strategies and protocols that allow these agents to interrupt their strategy to avoid exploitation and unfavorable agreements. Outcomes of simulation runs are compared across systems and to human negotiation along various outcome dimensions - proportion of agreements, dyadic and individual performance, and fairness - for various negotiation problems derived from negotiation experiments with human subjects. Though there exist trade-offs between the different outcome dimensions, systems consisting of software agents, that systematically propose offers of monotonically decreasing utility and make first concession steps if the opponent reciprocated previous concessions, and an interaction protocol that enables to reject unfavorable offers - without immediately aborting negotiations - in order to elicit new offers from the opponent, performed best. These systems performed very well in all outcome dimensions when compared with other systems and were the only that outperformed negotiation between humans in all dimensions