Validation of agent-based land use model by Markovian model : application to forest-agriculture transitions in Madagascar

The determination of transition rules that farmers adopt to manage crop-fallow after forest clearing, is essential for deciding a sustainable strategy for forest conservation. The effect of the type of farms with respect to these transition rules in forest border may mitigate incentive measures planned by forest conservation policy. Agent-base modeling (ABM) of land use is a relevant approach to manage the dynamics of heterogeneous mosaic landscapes such as the border of the Malagasy Eastern rainforest. Transition rules between six land uses (forest, fallow, crop, grass, plantation and paddy ?eld) are formalized at a plot level. A historical database containing transitions between the ?rst four land use states was used to calibrate transition models for the ecological and farmer land use dynamics. Three land-use models have been built: (1) a Markov chain (stochastic), (2) a timed automaton (deterministic), (3) and an agent-based model, which introduces the farmers. The land use ABM allows to test scenarios of deforestation with both varying initial population and farm spatial organization, size or strategy. The land use ABM is ?rst calibrated via a timed automaton, ?tting time delay parameters, the duration of each land use state (fallow, crop, grass), and the number of cropping cycles since the ?rst forest clearing. It is then validated with the help of a Markovian model, comparing two transition matrices with ?2 metrics. The two transition matrices were respectively created with historical data of plot land use, and with simulated data produced by the land use ABM. We ?nish with a general discussion on the validation of such a complex system with a simple mathematical model. (Résumé d'auteur

Automated observation of multi-agent based simulations: a statistical analysis approach

International audienceMulti-agent based simulations (MABS) have been successfully used to model complex systems in different areas. Nevertheless a pitfall of MABS is that their complexity increases with the number of agents and the number of different types of behavior considered in the model. For average and large systems, it is impossible to validate the trajectories of single agents in a simulation. The classical validation approaches, where only global indicators are evaluated, are too simplistic to give enough confidence in the simulation. It is then necessary to introduce intermediate levels of validation. In this paper we propose the use of data clustering and automated characterization of clusters in order to build, describe and follow the evolution of groups of agents in simulations. These tools provides the modeler with an intermediate point of view on the evolution of the model. Those tools are flexible enough to allow the modeler to define the groups level of abstraction (i.e. the distance between the groups level and the agents level) and the underlying hypotheses of groups formation. We give an online application on a simple NetLogo library model (Bank Reserves) and an offline log application on a more complex Economic Market Simulation

A Very Fast (Linear Time) Distributed Algorithm, on General Graphs, for the Minimum-Weight Spanning Tree

International audienceThis paper develops linear time distributed algorithm, on general graphs, for the minimum spanning tree, in asynchronous communication network. We concentrated our efforts on the improvement of the execution time this is why our algorithm is faster than all previous linear algorithms. Our algorithm propose a solution for computing the MST in time $n/2$ with $O(n^2)$ messages (where $n=|V|$ for a graph $G=(V,E)$). The total number of messages in the worst case is slightly higher than the others algorithms, but in practice is often better

Modeling visual attention on scenes

International audienceLa modélisation computationelle de l'attention visuelle connaît actuellement un essor considérable. Les premières modèles, purement basés sur l'attention dite exogène, permettent de calculer une carte de saillance indiquant les zones d'intérêt visuel d'une image. Cependant, afin d'améliorer cette prédiction, il s'avère nécessaire de prendre en compte des informations de plus haut niveaux relatives à l'attention endogène, c'est à dire des informations liées aux processus cognitifs. Afin de rendre compte de cette problématique, le présent article décrit un certain nombre de modèles exogènes ainsi que des modèles intégrant de la connaissance a priori. Les méthodes d'évaluation des performances sont également décrites. Afin d'aller plus loin dans la modélisation et dans la compréhension des processus cognitifs, de nouvelles perspectives et direction d'études sont exposées

Unreliable Distributed Timing Scrutinizer to Converge toward Decision Conditions

International audienceIn this paper, we propose to extend the condition-based approach introduced and developed by Most'efaoui et al. in 2001 by characterizing Vn f , the set of all the possible input vectors containing the values proposed by n processes. The condition-based approach consists in identifying sets of input vectors for which the consensus is directly solvable (i.e., in one communication step) in a pure asynchronous model despite up to f crashes. We focus on all the other input vectors. Among them, we identify those that allow to solve the consensus problem in two communication steps still in a pure asynchronous model. For the other ones, we rely on a distributed oracle that enables the input vectors to converge toward a good patterned vector with probability one. We specify a protocol that benefits from this approach to solve the consensus problem very simply and efficiently

Software Architecture of Code Analysis Frameworks Matters: The Frama-C Example

Implementing large software, as software analyzers which aim to be used in industrial settings, requires a well-engineered software architecture in order to ease its daily development and its maintenance process during its lifecycle. If the analyzer is not only a single tool, but an open extensible collaborative framework in which external developers may develop plug-ins collaborating with each other, such a well designed architecture even becomes more important. In this experience report, we explain difficulties of developing and maintaining open extensible collaborative analysis frameworks, through the example of Frama-C, a platform dedicated to the analysis of code written in C. We also present the new upcoming software architecture of Frama-C and how it aims to solve some of these issues.Comment: In Proceedings F-IDE 2015, arXiv:1508.0338

Unreliable Distributed Timing Scrutinizer to Converge toward Decision Conditions

International audienceIn this paper, we propose to extend the condition-based approach introduced and developed by Most'efaoui et al. in 2001 by characterizing Vn f , the set of all the possible input vectors containing the values proposed by n processes. The condition-based approach consists in identifying sets of input vectors for which the consensus is directly solvable (i.e., in one communication step) in a pure asynchronous model despite up to f crashes. We focus on all the other input vectors. Among them, we identify those that allow to solve the consensus problem in two communication steps still in a pure asynchronous model. For the other ones, we rely on a distributed oracle that enables the input vectors to converge toward a good patterned vector with probability one. We specify a protocol that benefits from this approach to solve the consensus problem very simply and efficiently

О комбинаторной структуре задач оптимального размещения геометрических объектов

Рассматривается задача оптимального размещения геометрических объектов с заданными формой и фиксированными физико-метрическими параметрами. Выделяется комбинаторная структура задачи путем формирования множества кортежей физико-метрических параметров. На основе функционального представления множества перестановок кортежей формулируется эквивалентная постановка, в которой физико-метрические параметры рассматриваются как независимые переменные. Предложенный подход иллюстрируется при решении задачи упаковки кругов заданных радиусов в круге минимального радиуса.Розглядається задача оптимального пакування геометричних об'єктів заданої форми та фіксованих фізико-метричних параметрів. Виділена комбінаторна структура задачі шляхом формування множини кортежів фізико-метричних параметрів. На підставі функціонального представлення множини перестановок кортежів формулюється еквівалентна постановка зі змінними фізико-метричними параметрами. Запропонований підхід ілюструється при розв'язанні задачі пакування кіл заданих радіусів у колі мінімального радіуса.The problem of optimal layout of geometric objects with given shape and physico-metric parameters is considered. Combinatorial structure is allocated by forming the multiple tuples of physico-metric parameters. On the basis of a functional presentation of the permutations of tuples, an equivalent setting, in which physico-metric parameters are variables, is formulated. The proposed approach is illustrated by the problem of packing of unequal circles into a circle with minimal radius