Publications, papers published in July 1999/communications publiées en juillet 1999

Bibliography

1

D. Alazard, P. Apkarian, and S. Mauffrey.
Exact observer based structures for arbitrary full order compensators.
In IFAC 99 - 14th World Congress, Beijing (Chine), 5 - 7 July 1999. IFAC.
In this paper, some new techniques for determining the observer-based or LQG form of any full-order compensator, that is, a compensator whose order is the same as the plant's order, are discussed. The practical appeal of such techniques is that they allow for a simplified implementation and reduced memory storage of general controllers and offer additional flexibility for handling gain-scheduling and input saturation constraints. The derived observer-based controllers are input-output equivalent to the original controller but with an explicit separated estimation/control structure and an extra Youla parameter. Necessary conditions to apply this general controller equivalence principle are derived. The interest and practicality of such techniques are then investigated with regards to the LQG implementation of and controllers, classes of controllers that does not generally enjoy ease of implementation. In particular, these aspects have revealed to be of crucial importance for the applicability of the technique to attitude control of launchers.

2

P. Fabiani and J. C. Latombe.
Dealing with geometric constraints in game-theoretic planning.
In IJCAI'99, Stockholm (Sweden), 31 July-6 August 1999. Sponsored by IJCAII and the Scandinavian AI Societies.
Tracking a partially predictable moving object in a workspace cluttered by obstacles is a challenging combination of two planning problems. The planner must take into account on the one hand the visibility and motion constraints imposed by the obstacles and on the other hand the uncertainties in both the robot's position and the future trajectory of the target. Game theory is proposed as an appropriate framework to solve this twofold problem. At each time step, a probability distribution models the positioning uncertainties of the robot and the target and a utility function represents the reward associated with the possible goal states of the motion decision problem. This approach allows the simple modeling of different tracking strategies, one of which has been implemented and tested successfully with two mobile robots. By considering simultaneously target visibility and position uncertainty, the tracking robot can take advantage of landmarks scattered in the workspace to better localize itself so as to better track the target afterward. Future extensions seem possible in order to introduce useful symbolic inferences within the game-theoretic framework.

3

D. Martinez, G. Verfaillie, and C. Bessière.
A generic customizable framework for inverse local consistency.
In Sixteenth National Conference on Artificial Intelligence (AAAI-99), pages 169-174, Orlando, Florida (USA), 18 - 22 July 1999. AAAI.
Local consistency enforcing is at the core of CSP (Constraint Satisfaction Problem) solving. Although arc consistency is still the most widely used level of local consistency, researchers are going on investigating more powerful levels, such as path consistency, k-consistency, (i,j)-consistency. Recently, more attention has been turned to inverse local consistency levels, such as path inverse consistency, k-inverse consistency, neighborhood inverse consistency, which do not suffer from the drawbacks of the other local consistency levels (changes in the constraint definitions and in the constraint graph, prohibitive memory requirements). In this paper, we propose a generic framework for inverse local consistency, which includes most of the previously defined levels and allows a rich set of new levels to be defined. The first benefit of such a generic framework is to allow a user to define and test many different inverse local consistency levels, in accordance with the problem or even the instance he/she has to solve. The second benefit is to allow a generic algorithm to be defined. This algorithm, which is parameterized by the chosen inverse local consistency level, generalizes the AC7 algorithm used for arc consistency, and produces from any instance its locally consistent closure at the chosen level.

4

L. Chaudron and M. Boyer.
Mocou : un nouvel outil de modélisation de la gêne sonore.
Acoustique et Techniques, (18):43-47, juillet 1999.
Dans cet article, nous présentons une démarche visant à concevoir un outil générique de corrélation entre les bruits générés par les mouvements d'avions d'un aéroport et la gêne qu'ils occasionnent aux riverains. L'étude s'inscrit dans le cadre de l'intelligence artificielle et plus particulièrement sur le thème des relations entre des systèmes artificiels et des utilisateurs involontaires. Il s'agit dans une première étape de poser correctement l'ensemble des problèmes qui s'imposent aux différents acteurs en présence (avions, compagnies, aéroports, riverains, collectivités locales...) afin de contribuer à l'expression de résolutions adaptées ; bien au delà d'une simple fonction croissante "niveau de bruit" -> "gêne", on cherche à détailler l'expression interne de relations de causalités entre certaines caractéristiques précisément déterminées des bruits et les paramètres correspondant de la gêne effectivement ressentie. Ceci suppose l'élaboration progressive de modèles cognitifs de gêne, mais aussi des modèles de couplages entre systèmes artificiels et êtres humains. Pour conserver une sémantique aussi riche que possible les modèles définis et utilisés visent à être aussi simples, génériques et expressifs que possible, d'où le recours privilégié aux formalismes symboliques. La présente étude doit donc être comprise comme un programme à long terme. Nous en présentons ici les éléments de base : i) le programme expérimental, ii) le modèle théorique utilisé, iii) les étapes en cours.

5

L. Chaudron and C. Tessier.
AAAI'99 workshop "agents conflicts".
In C. Tessier and AAAI Press L. Chaudron, editors, Papers from the AAAI Workshop, ISBN 1-57735-092-8, Orlando, Florida (USA), 18 - 18 July 1999. American Association for Artificial Intelligence.
Agents' conflicts arise for different reasons, involve different concepts, and are dealt with in different ways, depending on the kind of agents and on the domain where they are considered. For example, agents may have conflicting beliefs, conflicting goals, or may have to share limited resources. Conflicts can be expressed as mere differences, or as contradictions, or even as social conflicts (e.g. aggression, fighting). They may be avoided, solved, kept, or even created deliberately. Since more and more concern is attached to agents' teamwork and agents' dialogue, conflicts naturally arise as a key issue to be dealt with, not only with application dedicated techniques, but also with more formal and generic tools. The aim of the workshop is therefore to focus on definitions of agents' conflicts and on their roles within a multiagent system, i.e. how this system may evolve thanks to, despite, or because of conflicts.

6

J.-F. Magni, B. Girouart, C. Chiappa, C. Döll, and C. Chiappa.
Mixed mu-analysis for flexible structures. part 2: Application to the SPOT family of earth observation satellites.
In Proceeding of 14th IFAC World Congress, volume P, pages 325-360, Beijing (Chine), 5 - 9 July 1999. IFAC.
This paper presents new tools for computing upper and lower bounds of mu without frequency gridding. The proposed techniques for computing lower bounds of the peaks of the mu-curve, are divided into two steps. The first one consists of finding the perturbation with minimum Frobenius norm that leads to the limit of stability. Using this result as an initialization, the second algorithm finds the perturbation with minimum sigma-max norm such that the system remains at the limit of stability. The limit of stability is considered both from a state space and from a transfer matrix point of view, which leads to two classes of techniques. The lower bounds are validated by using an upper-bound analysis technique that considers standard scalings over a range of frequencies instead of at an isolated frequency.

7

C. Cossart and C. Tessier.
Filtering vs revision and update: let us debate!
In ECSQARU'99 -Fifth european Conference on Symbolic & Quantitative Approches to Reasoning with Uncertainty, Londres (UK), 5 - 9 July 1999. University College London.
Recent extensions of classical belief change processes tend to get closer to numerical estimation techniques. A thorough investigation is proposed, in which Kalman filtering is confronted to classical AGM revision and KM update and to more recent approaches. The aim is to identify common aspects and differences, and to highlight the progressive evolution of belief change processes towards what would be a symbolic transposition of numerical estimation tools.

8

H. Fiorino and C. Tessier.
Common belief elaboration by cooperating agents.
In IJCAI'99 - 16th International Joint Conference on Artificial Intelligence, Stockholm, Sweden., 31 July-6 August 1999.
Within the context of a team of agents having individual beliefs, our goal is to characterize and define the team's common belief, without considering such parameters as agents' reliabilities. This enables us to make the most of the agents' own beliefs and to account for the team's intrinsic uncertainty, especially when some agents disagree.
The agents' beliefs are defined as a preference relation. Conflicts are formally defined and the common belief, which is considered as a fusion of the preference relations, is characterized. A pragmatic operator to elaborate the common belief is proposed. Finally, properties of the common belief are highlighted, especially when the agents' preferences are based on Hamming's distance.

9

J.-F. Magni, C. Döll, C. Chiappa, B. Frappard, and B. Girouart.
Mixed mu-analysis for flexible structures. part 1 :theory.
In Proceeding 14th IFAC World Congress, volume P, pages 325-360, Beijing (Chine), 12 - 17 July 1999. IFAC.
JeanFrançois à toi de mettre coller le résumé merci.

10

B. Frapard, B. Girouart, C. Döll, J.-F. Magni, and C. Chiappa.
Mixed mu-analysis for flexible structures. part 2: Application to the SPOT family of earth observation satellites.
In IEEE, editor, Proceeding of 14th IFAC World Congress, volume P, pages 361-366, Beijing (Chine), 5 - 9 July 1999.
Mixed-mu-analysis of the companion paper (magni, ifac 99) is a new tool introduced to support the control system design process on complex, multivariable flexible dynamic systems. In the present paper the transfer from research to application is described. The example retained is the SPOT satellite developed at MMS for earth imagery. The specificities of flexible large Space structures are correctly accounted for by the new tools, as they offer the capacity to track very narrow resonant peaks. All known worst case combinations of modal characteristics of the flexible structure were obtained in a very reliable way, requiring less than 10 to 20 minutes on a Sparc 5 station, for a 70th order system and a 20th order uncertain vector with repeated terms. Large variations of up to some 50 % in the real uncertainties were dealt with, thus covering what can be experienced in a 5 years on-orbit lifetime. as well as non-intuitive though meaningful worst-case combinations were discovered constituting for the SPOT project team a source of useful information for control improvement.

11

M. Lemaître, G. Verfaillie, and N. Bataille.
Exploiting a common property resource under a fairness constraint: a case study.
In Sixteenth International Joint Conference on Artificial Intelligence (IJCAI-99), pages 206-211, Stockholm (Sweden), 31 July-6 August 1999. Sponsored by IJCAII and the Scandinavian AI Societies.
Resources co-funded by several agents must be exploited in such a way that three kinds of constraints are met: (1) physical problem (hard) constraints; (2) efficiency constraints, aiming at maximizing the satisfaction of each agent; (3) a fairness constraint, which is ideally satisfied when each agent receives an amount of the resource exactly proportional to its financial contribution. This paper investigates a decision problem for which the common property resource is an earth observation satellite. The problem is to decide on the daily selection of a subset of pictures, among a set of candidate pictures which could be taken the next day considering the satellite trajectory. This subset must satisfy the three kinds of constraints stated above. Although fair division problems have received considerable attention for a long time, especially from microeconomists, this specific problem does not fall entirely within a classical approach. This is because the candidate pictures may be incompatible, and because a picture is only of value to the agent requesting it. As in the general case, efficiency and fairness constraints are antagonistic. We propose three ways for solving this share problem. The first one gives priority to fairness, the second one to efficiency, and the third one computes a set of compromises.

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