arXiv subjects

Régis Sabbadin

Publications and source records attributed to Régis Sabbadin.

4 recordsLinked to original sources

arXiv2026

Bridging Impulse Control of Piecewise Deterministic Markov Processes and Markov Decision Processes: Frameworks, Extensions, and Open Challenges

Control theory plays a pivotal role in understanding and optimizing the behavior of complex dynamical systems across various scientific and engineering disciplines. Two key frameworks that have emerged for modeling and solving control problems in stochastic systems are piecewise deterministic Markov processes (PDMPs) and Markov decision processes (MDPs). Each framework has its unique strengths, and their intersection offers promising opportunities for tackling a broad class of problems, particularly in the context of impulse controls and decision-making in complex systems. The relationship between PDMPs and MDPs is a natural subject of exploration, as embedding impulse control problems for PDMPs into the MDP framework could open new avenues for their analysis and resolution. Specifically, this integration would allow leveraging the computational and theoretical tools developed for MDPs to address the challenges inherent in PDMPs. On the other hand, PDMPs can offer a versatile and simple paradigm to model continuous time problems that are often described as discrete-time MDPs parametrized by complex transition kernels. This transformation has the potential to bridge the gap between the two frameworks, enabling solutions to previously intractable problems and expanding the scope of both fields. This paper presents a comprehensive review of two research domains, illustrated through a recurring medical example. The example is revisited and progressively formalized within the framework of thevarious concepts and objects introduced

stat.ME↗

arXiv2024

Medical follow-up optimization: A Monte-Carlo planning strategy

Designing patient-specific follow-up strategy is a crucial step towards personalized medicine in cancer. Tools to help doctors deciding on treatment allocation together with next visit date, based on patient preferences and medical observations, would be particularly beneficial. Such tools should be based on realistic models of disease progress under the impact of medical treatments, involve the design of (multi-)objective functions that a treatment strategy should optimize along the patient's medical journey, and include efficient resolution algorithms to optimize personalized follow-up by taking the patient's history and preferences into account. We propose to model cancer evolution with a Piecewise Deterministic Markov Process where patients alternate between remission and relapse phases with disease-specific tumor evolution. This model is controlled via the online optimization of a long-term cost function accounting for treatment side-effects, hospital visits burden and disease impact on the quality of life. Optimization is based on noisy measurements of blood markers at visit dates. We leverage the Partially-Observed Monte-Carlo Planning algorithm to solve this continuous-time, continuous-state problem, taking advantage of the nearly-deterministic nature of cancer evolution. We show that this approximate solution approach of the exact model performs better than the counterpart exact resolution of the discrete model, while allowing for more versatility in the cost function model.

math.OC↗

arXiv2020

Improving Pest Monitoring Networks in order to reduce pesticide use in agriculture

Disease and pest control largely rely on pesticides use and progress still remains to be made towards more sustainable practices. Pest Monitoring Networks (PMNs) can provide useful information for improving crop protection by restricting pesticide use to the situations that best require it. However, the efficacy of a PMN to control pests may depend on its spatial density and space/time sampling balance. Furthermore the best trade-off between the monitoring effort and the impact of the PMN information may be pest dependent. We developed a generic simulation model that links PMN information to treatment decisions and pest dynamics. We derived the number of treatments, the epidemic extension and the global gross margin for different families of pests. For soil-borne pathogens and weeds, we found that increasing the spatial density of a PMN significantly decreased the number of treatments (up to 67\%), with an only marginal increase in infection. Considering past observations had a second-order effect (up to a 13\% decrease). For the spatial scale of our study, the PMN information had practically no influence in the case of insects. The next step is to go beyond PMN analysis to design and chose among sustainable management strategies at the landscape scale.

q-bio.PE↗

arXiv2018

Exact and approximate inference in graphical models: variable elimination and beyond

Probabilistic graphical models offer a powerful framework to account for the dependence structure between variables, which is represented as a graph. However, the dependence between variables may render inference tasks intractable. In this paper we review techniques exploiting the graph structure for exact inference, borrowed from optimisation and computer science. They are built on the principle of variable elimination whose complexity is dictated in an intricate way by the order in which variables are eliminated. The so-called treewidth of the graph characterises this algorithmic complexity: low-treewidth graphs can be processed efficiently. The first message that we illustrate is therefore the idea that for inference in graphical model, the number of variables is not the limiting factor, and it is worth checking for the treewidth before turning to approximate methods. We show how algorithms providing an upper bound of the treewidth can be exploited to derive a 'good' elimination order enabling to perform exact inference. The second message is that when the treewidth is too large, algorithms for approximate inference linked to the principle of variable elimination, such as loopy belief propagation and variational approaches, can lead to accurate results while being much less time consuming than Monte-Carlo approaches. We illustrate the techniques reviewed in this article on benchmarks of inference problems in genetic linkage analysis and computer vision, as well as on hidden variables restoration in coupled Hidden Markov Models.

stat.ML↗