All Years Seminars
[INMA] 2023-05-02 (14h) : Understanding human motor control and adaptation through stochastic feedback control
At Euler building (room A.002)
Speaker :
Kalidindi, Hari Teja
Abstract :
Humans display flexible motor control in a wide range of contexts, which is supported by distributed computations in the nervous system. Stochastic optimal feedback control models have been used to capture many features of human motor behavior and related neural information processing (to an extent), but their use has been limited to well-practiced movement repertoires, where human behavior is observed to be close to optimal. However, when the conditions under which humans act change, they must adapt their control responses to suit the new context. Although adaptive behavior involves optimizing one's actions to new contexts, researchers have surprisingly avoided using optimal feedback control models to explain motor adaptation until very recently. In my presentation, I will discuss how stochastic feedback control is used in neuroscience and our work on human motor control and adaptation, which is based on predictions from this theory. Overall, my presentation will demonstrate the importance of considering stochastic feedback control in our understanding of human motor control and adaptation and how it can shed light on how the nervous system produces movements.
[INMA] 2023-04-25 (14h) : Ranking from pairwise comparisons: a near-linear time minimax optimal algorithm for learning BTL weights
At Euler building (room A.002)
Speaker :
Hendrickx, Julien
Abstract :
We consider the problem of ranking and learning the qualities w1,…,wn of a collection of items by performing noisy comparisons among them. We assume that there is a fixed “comparison graph”, and every neighboring pair of items is compared k times.
We focus more specifically on the popular Bradley-Terry-Luce model, where comparisons are i.i.d. events, and the probability for item i to win the comparison against j is wi/(wi+wj).
We propose a near-linear time algorithm allowing us to recover the weights with an accuracy that outperforms all existing algorithms, and show that this accuracy is actually within a constant factor of information-theoretic lower bounds, that we also develop. This accuracy is related to the average resistance of the comparison graph.
Our algorithm is based on a weighted least square, with weights determined from empirical outcomes of the comparisons.
We further discuss the extension to other models of comparisons, and comparisons involving multiple items.
[INMA] 2023-04-18 (14h) : Lambda-determinants and other tilings problems
At Euler building (room A.002)
Speaker :
Philippe Ruelle (UCLouvain)
Abstract :
We will review (some of) the connections between lambda-determinants and tiling problems. Along the way this will give us the opportunity to recall the story of alternating sign matrices.
[INMA] 2023-03-21 (14h) : Towards a Unified Perspective to Observer Design
At Euler building (room A.002)
Speaker :
Pauline Bernard (Mines Paris)
Abstract :
We start by reviewing the main techniques of state observer design for continuous-time dynamical systems. Starting from necessary conditions for the existence of such asymptotic observers, we classify the available methods depending on the detectability/observability assumptions they require. We show that each class of observer relies on transforming the system dynamics into a particular normal form which allows the design of an observer, and how each observability condition guarantees the invertibility of its associated transformation and the convergence of the observer. Then, we give a particular focus to the theory of KKL or nonlinear Luenberger observers. This design consists in looking for a change of coordinates changing the system dynamics into a contracting filter of the output. A state estimate is then obtained by implementing this filter from any initial condition and left-inverting the transformation, which is shown to be possible under a very weak backward-distinguishability property. We show how, unlike other methods, this idea is universal and can be extended to any type of dynamical systems (continuous or discrete time, autonomous or discrete, observable or non-observable, etc), thus offering a promising road towards a unified paradigm for observer design.
[INMA] 2023-03-14 (14h) : Welcome Seminar
At Euler building (room a.002)
Section 1:Randomness in Electronic Devices and Circuits
Speaker :
Van Brandt, Léopold
Abstract : The MOS transistors of smallest dimensions (below 100 nm), universally favoured for the design of digital integrated silicon circuits, are very sensitive to all types of uncertainties, notably statistical process variability. Multiple variability sources of various physical origins introduce random device-to-device fluctuations in the transistor parameters and thereby affect the performance of the circuits. In this presentation, we will mainly focus on the prediction of the failure probability of Static Random Access Memory (SRAM) bitcells. The estimation of probabilities as extremely low as the ppm (i.e. parts-per-million) with limited computational resources and time is a challenge. We will start by emphasising the limitations of the conventional Monte-Carlo simulation approach, before introducing our semi-analytical prediction methodology that turns out to be fast, accurate and insightful. We will close this talk by mentioning some on-going work, where we attempt to apply fundamental physical results to electronic devices and circuits.
Section 2:Lyapunov functions for open multi-agent dynamics
Speaker :
Renato Vizuete (CentraleSupélec and GIPSA-lab, France )
Abstract : Open multi-agent dynamics are systems characterized by arrivals, departures, or replacements of agents during the evolution of the dynamics. These types of systems are better approximations of modern networks where agents constantly enter and leave the systems, modifying the behavior of the group (e.g., social networks, epidemics, vehicle platoons, swarm of robots). Unfortunately, due to the complexity of the analysis, most of the works have been focused on linear systems, which are limited to few practical applications. In this talk, we present an approach based on Lyapunov functions for the analysis of more complex open multi-agent dynamics where arrivals, departures and replacements are determined by stochastic processes. In the first part, we introduce the techniques based on the formulation of stochastic differential equations with an application to a SIS epidemic subject to replacements of agents. In the second part, by analyzing the Hegselmann-Krause dynamics, we show that some common Lyapunov functions might not be adequate in open scenarios characterized by arrivals and departures of agents.
Seminars
Subscribe (ICS)
INMA Contact Info
Mathematical Engineering (INMA)
L4.05.01
Avenue Georges Lemaître, 4
+32 10 47 80 36
secretaire-inma@uclouvain.be
Mon – Fri 9:00A.M. – 5:00P.M.
JOIN US