All Years Seminars
[INMA] 2025-08-20 (14h) : Efficient Distance-Adaptive Subgradient Methods
At Euler building (room A.002)
Speaker :
Anton Rodomanov (CISPA, Germany)
Abstract :
Subgradient methods based on the idea of gradient normalization are an appealing class of algorithms for convex optimization because they automatically adapt to the local growth rate of the objective and require no problem-specific parameters---except for a reasonably accurate estimate of the initial distance to the solution. Overestimating or underestimating this distance can, however, substantially slow convergence. We address this limitation by incorporating into normalization-based methods a recently proposed technique that dynamically estimates the distance via the displacement of iterates from the starting point. This removes the need for any problem-specific information, while preserving the adaptability of the base methods and ensuring rigorous convergence guarantees. Illustrative examples include nonsmooth Lipschitz functions, Lipschitz- or Hölder-smooth functions, functions with high-order Lipschitz derivatives, quasi-self-concordant functions, and $(L_0, L_1)$-smooth functions. We further extend the approach to problems with functional constraints using a simple switching strategy.
[INMA] 2025-06-17 (14h) : Matrix Factorization and Approximation of Nonnegative Rank Two
At Euler building (room A.002)
Speaker :
Van Dooren, Paul
Abstract :
We consider the problem of finding the best nonnegative rank two approxi-
mation of an arbitrary nonnegative matrix. We first provide a parametrization
of all possible nonnegative factorizations of a nonnegative matrix of rank 2. We
then use this result to construct a suboptimal, but cheaply computable, solution
of the nonnegative rank 2 approximation problem for an arbitrary nonnegative
matrix input; this can then be used as a starting point for the Alternating Least
Squares method, resulting in both an improved computational complexity and
an enhanced output quality. We provide numerical experiments to support these
claims. We also look at some variants of the problem, including symmetry con-
straints and three-way factorizations.
This is joint work with Etna Lindy and Vanni Noferini (Aalto University).
[INMA] 2025-05-20 (14h) : Model-Based and Data-Driven Interventions in Network Games
At Euler building (room A.002)
Speaker :
Nima Monshizadeh (University of Groningen)
Abstract :
In modern cyber-physical-human systems like power grids and traffic networks, self-interested decisions by users or firms often lead to inefficiencies such as congestion, blackouts, and systemic risks. These challenges underscore the need for effective intervention mechanisms to coordinate self-interested behavior. However, designing effective interventions with guaranteed performance is challenging, as planners typically lack detailed knowledge of users’ private preferences or behaviors. This informational gap and privacy considerations complicate the prediction of user responses and hinder the development of suitable control strategies. In this talk, we examine the problem of intervention design in network games, where agents’ cost or utility functions are interdependent; as exemplified by applications such as multi-commodity markets. The central question is how the type of information available to the planner — ranging from full to partial knowledge of utility functions, network structure, or desired target profiles — shapes the design of effective interventions. We also give special attention to scenarios in which the planner has no a priori knowledge of agent cost functions and must rely instead on historical observations of agent actions and past interventions. Given these diverse informational settings, we discuss a range of static, dynamic, adaptive, and data-driven intervention strategies aimed at steering the system toward socially desirable outcomes. The results illustrate how combining control-theoretic, game-theoretic, and data-driven insights enables the design of interventions that are effective under various informational constraints.
[INMA] 2025-05-06 (14h) : Axisymmetric magnetic control in ST40
At Euler building (room A.002)
Speaker :
Benjamin Vincent (UCLouvain)
Abstract :
Tokamaks magnetically confine plasmas (i.e. ionised gas) up to temperatures where the nuclear fusion reaction is sustainable. The real-time operation of a tokamak relies on a Plasma Control System, which is responsible for data acquisition, pulse supervision and feedback control. The plasma current, position, and shape can be actuated by the poloidal field coils.
The talk will introduce the concept of tokamaks and magnetically confined plasmas. The axisymmetric magnetic control problems will be presented and illustrated in the context of the spherical tokamak ST40.
[INMA] 2025-04-16 (15h) : Gradient-based optimization in CFD: from nuclear fusion to small modular fission reactors
At Euler building (room A.002)
Speaker :
Niels Horsten (IMMC,UCLouvain)
Abstract :
Gradient-based optimization is a powerful tool for advancing engineering applications. Its success relies on three key ingredients: accurate simulation models, efficient gradient calculations, and carefully chosen optimization methods. In this seminar, I will demonstrate how I developed fast, physics-based CFD models for nuclear fusion that are now being used for the design of future reactors. A particular focus will be on the challenges and solutions for obtaining gradients from Monte Carlo particle simulations, which are critical for modeling neutral-plasma interactions in fusion and neutron transport in fission systems. Lastly, I will discuss the application of these methods to the design of heat exchangers for lead-cooled small modular reactors (SMRs). The unique properties of liquid lead, particularly its low Prandtl number, introduce additional complexities for the optimization.
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