Statistical Model Checking for Stochastic Hybrid Systems

This paper presents novel extensions and applications of the UPPAAL-SMC model checker. The extensions allow for statistical model checking of stochastic hybrid systems. We show how our race-based stochastic semantics extends to networks of hybrid systems, and indicate the integration technique applied for implementing this semantics in the UPPAAL-SMC simulation engine. We report on two applications of the resulting tool-set coming from systems biology and energy aware buildings.Comment: In Proceedings HSB 2012, arXiv:1208.315

Runtime Verification of Biological Systems

International audienceComplex computational systems are ubiquitous and their study increasingly important. Given the ease with which it is possible to construct large systems with heterogeneous technology, there is strong motivation to provide automated means to verify their safety, efficiency and reliability. In another context, biological systems are supreme examples of complex systems for which there are no design specifications. In both cases it is usually difficult to reason at the level of the description of the systems and much more convenient to investigate properties of their executions. To demonstrate runtime verification of complex systems we apply statistical model checking techniques to a model of robust biological oscillations taken from the literature. The model demonstrates some of the mechanisms used by biological systems to maintain reliable performance in the face of inherent stochasticity and is therefore instructive. To perform our investigation we use two recently developed SMC platforms: that incorporated in Uppaal and Plasma. Uppaalsmc offers a generic modeling language based on stochastic hybrid automata, while Plasma aims at domain specific support with the facility to accept biological models represented in chemical syntax

A logic of behaviour in context

AbstractWe present a novel temporal logic for expressing properties of behaviour in context. The logic is applied to models of continuous processes, specifically using the continuous π-calculus as a modelling language for biochemical systems.The logic allows the expression of the temporal behaviour of a system when placed in the context of another system. Here we study this in terms of biochemical reactions and the expression of temporal behaviour in the context of other biochemical processes. We present the syntax and semantics of the logic and study the model-checking problem over continuous time and continuous state-space process models, using the continuous π-calculus.We present a succinct, but naive, model-checking algorithm and then show how this can be improved. We investigate the complexity of model-checking, where repeated ODE solving emerges as a particular cost; assess some limitations of the technique; and identify potential routes to overcome these

monitor-based statistical model checking for weighted metric temporal logic

We present a novel approach and implementation for analysing weighted timed automata (WTA) with respect to the weighted metric temporal logic (WMTL &le). Based on a stochastic semantics of WTAs, we apply statistical model checking (SMC) to estimate and test probabilities of satisfaction with desired levels of confidence. Our approach consists in generation of deterministic monitors for formulas in WMTL&le, allowing for efficient SMC by run-time evaluation of a given formula. By necessity, the deterministic observers are in general approximate (over- or under-approximations), but are most often exact and experimentally tight. The technique is implemented in the new tool Casaal. that we seamlessly connect to Uppaal-smc. in a tool chain. We demonstrate the applicability of our technique and the efficiency of our implementation through a number of case-studies. © 2012 Springer-Verlag.Microsoft ResearchWe present a novel approach and implementation for analysing weighted timed automata (WTA) with respect to the weighted metric temporal logic (WMTL &le). Based on a stochastic semantics of WTAs, we apply statistical model checking (SMC) to estimate and test probabilities of satisfaction with desired levels of confidence. Our approach consists in generation of deterministic monitors for formulas in WMTL&le, allowing for efficient SMC by run-time evaluation of a given formula. By necessity, the deterministic observers are in general approximate (over- or under-approximations), but are most often exact and experimentally tight. The technique is implemented in the new tool Casaal. that we seamlessly connect to Uppaal-smc. in a tool chain. We demonstrate the applicability of our technique and the efficiency of our implementation through a number of case-studies. © 2012 Springer-Verlag

Monitor-Based Statistical Model Checking for Weighted Metric Temporal Logic

International audienceWe present a novel approach and implementation for analysing weighted timed automata (WTA) with respect to the weighted metric temporal logic (WMTL≤). Based on a stochastic semantics of WTAs, we apply statistical model checking (SMC) to estimate and test probabilities of satisfaction with desired levels of confidence. Our approach consists in generation of deterministic monitors for formulas in WMTL≤, allowing for efficient SMC by run-time evaluation of a given formula. By necessity, the deterministic observers are in general approximate (over- or under-approximations), but are most often exact and experimentally tight. The technique is implemented in the new tool Casaal that we seamlessly connect to Uppaal-smc in a tool chain. We demonstrate the applicability of our technique and the efficiency of our implementation through a number of case-studies

Model-Based Verification, Optimization, Synthesis and Performance Evaluation of Real-Time Systems

International audienceThis article aims at providing a concise and precise Travellers Guide, Phrase Book or Reference Manual to the timed automata modeling formalism introduced by Alur and Dill [8, 9]. The paper gives comprehensive definitions of timed automata, priced (or weighted) timed automata, and timed games and highlights a number of results on associated decision problems related to model checking, equivalence checking, optimal scheduling, the existence of winning strategies, and then statistical model checking

Towards Reliable Robotics: from Navigation to Coordination

Les robots autonomes et les systèmes multi-robots ont connu un intérêt sans cesse croissant par les scientifiques et l’industrie. Plusieurs applications telles que les robots assistants, les robots gestionnaires de stock ainsi que les véhicules autonomes nécessitent des algorithmes de navigation et de coordination fiables pour permettre leur déploiement dans des environnements dynamiques et relativement méconnus. Ainsi, la capacité d’adaptation est une caractéristique fondamentale permettant une utilisation accrue et une intégration plus facile des systèmes multi-robots. Afin de posséder cette agilité d’adaptation, les robots devraient opter vers un comportement assez robuste avec une aptitude à réajuster leurs actions selon la cinématique de l’environnement. Ce mémoire de thèse, s’interesse aux problèmes de fiabilité lors du déploiement des systèmes multi-robots dans des environnements dynamiques et inconnus. Il s’articule autour de deux contributions majeures, à savoir : Un mécanisme de planification et de réajustement de mouvement quasi optimal qui roule à une fréquence allant jusqu’à 200 Hz. Ainsi qu’un framework de vérification de la robustesse des comportements coopératifs des systèmes multi-robots. La première contribution a été inspirée de l’habilité de quelques animaux à naviguer en se fiant au champ magnétique terrestre. En effet, nous avons constaté que le champ magnétique n’admet pas de maxima locaux, ce qui permet aux animaux de suivre son gradient. Par conséquent, un robot est capable de parcourir tout type d’environnements en faisant propager un champ magnétique virtuel et en suivant son gradient. Toutefois, la résolution des équations de Maxwell, qui décrivent la physique des champs magnétiques, est complexe et nécessitent des simulations numériques couteuses en termes de ressources et temps de calcul. Pour pallier cette difficulté, nous proposons un approximateur de la solution des équations de Maxwell basé sur un réseau de neurones profond entrainé exclusivement sur des solutions provenant de simulations numériques avancées. L’environnement est représenté par une carte de conductivité. Nous affectons une conductivité maximale à la destination du robot et une conductivité nulle aux obstacles. Le calcul de la distribution du champ magnétique virtuel permettra au robot de suivre le gradient qui le mènera vers sa destination selon un chemin quasi optimal.----------ABSTRACT: Autonomous robots and multi-robot systems are of growing interest for industry and academia. Many real-world applications such as assistive robotics, inventory management, and autonomous driving require reliable navigation and coordination algorithms that can be deployed in a partially unknown, dynamic environment. The ability to adapt is a key feature for the widespread use and societal integration of multi-robot systems. To achieve this adaptation ability, robots must implement inherently robust behaviors and must be sufficiently fast to re-plan their actions when their environment changes. This dissertation deals with the problem of reliably deploying a group of robots in a dynamic, unknown environment, and provides two key contributions: a mechanism for robots to plan and re-plan their motion near optimally up to 200 times per second; and a framework to verify the robustness of multi-robot cooperative behaviors. For the first contribution, observing how some animals are able to navigate using the Earth’s magnetic field, we realize that this is possible because the magnetic field has no local maxima, and animals can follow its gradient. This means that a robot can navigate any kind of environment by propagating a known virtual magnetic field and following its gradient. However, solving Maxwell’s equations–which govern the physics of magnetic fields– is complex and demands computationally costly numerical simulations. To overcome this problem, we propose a deep neural network as an approximator for Maxwell’s equations, exclusively trained on high-quality numerical simulations. We model the environment as a conductivity map with its maximum in a goal location and zero for obstacles. After computing the virtual field propagation, a robot can follow the virtual magnetic gradient to optimally reach the goal

Contribution to the verification of timed automata (determinization, quantitative verification and reachability in networks of automata)

Cette thèse porte sur la vérification des automates temporisés, un modèle bien établi pour les systèmes temps-réels. La thèse est constituée de trois parties. La première est dédiée à la déterminisation des automates temporisés, problème qui n'a pas de solution en général. Nous proposons une méthode approchée (sur-approximation, sous-approximation, mélange des deux) fondée sur la construction d'un jeu de sûreté. Cette méthode améliore les approches existantes en combinant leurs avantages respectifs. Nous appliquons ensuite cette méthode de déterminisation à la génération automatique de tests de conformité. Dans la seconde partie, nous prenons en compte des aspects quantitatifs des systèmes temps-réel grâce à une notion de fréquence des états acceptants dans une exécution d'un automate temporisé. Plus précisément, la fréquence d'une exécution est la proportion de temps passée dans les états acceptants. Nous intéressons alors à l'ensemble des fréquences des exécutions d'un automate temporisé pour étudier, par exemple, le vide de langages seuils. Nous montrons ainsi que les bornes de l'ensemble des fréquences sont calculables pour deux classes d'automates temporisés. D'une part, les bornes peuvent être calculées en espace logarithmique par une procédure non-déterministe dans les automates temporisés à une horloge. D'autre part, elles peuvent être calculées en espace polynomial dans les automates temporisés à plusieurs horloges ne contenant pas de cycles forçant la convergence d'horloges. Finalement, nous étudions le problème de l'accessibilité des états acceptants dans des réseaux d'automates temporisés qui communiquent via des files FIFO. Nous considérons tout d'abord des automates temporisés à temps discret, et caractérisons les topologies de réseaux pour lesquelles l'accessibilité est décidable. Cette caractérisation est ensuite étendue aux automates temporisés à temps continu.This thesis is about verification of timed automata, a well-established model for real time systems. The document is structured in three parts. The first part is dedicated to the determinization of timed automata, a problem which has no solution in general. We propose an approximate (over-approximation/under-approximation/mix) method based on the construction of a safety game. This method improves both existing approaches by combining their respective advantages. Then, we apply this determinization approach to the generation of conformance tests. In the second part, we take into account quantitative aspects of real time systems thanks to a notion of frequency of accepting states along executions of timed automata. More precisely, the frequency of a run is the proportion of time elapsed in accepting states. Then, we study the set of frequencies of runs of a timed automaton in order to decide, for example, the emptiness of threshold languages. We thus prove that the bounds of the set of frequencies are computable for two classes of timed automata. On the one hand, we prove that bounds are computable in logarithmic space by a non-deterministic procedure in one-clock timed automata. On the other hand, they can be computed in polynomial space in timed automata with several clocks, but having no cycle that forces the convergence between clocks. Finally, we study the reachability problem in networks of timed automata communicating through FIFO channels. We first consider dicrete timed automata, and characterize topologies of networks for which reachability is decidable. Then, this characterization is extended to dense-time automata.RENNES1-Bibl. électronique (352382106) / SudocSudocFranceF