All Years Seminars
[INMA] 2019-02-05 (14:00) : Iterative regularization using proximal methods
At Euler building (room A.002)
Speaker :
Villa, Silvia
Abstract :
In the context of linear inverse problems, I will discuss iterative regularization methods allowing to consider large classes of data-fit terms and regularizers.In particular, I will investigate regularization properties of first order proximal splitting optimization techniques. Such methods are appealing since their computational complexity is tailored to the estimation accuracy allowed by the data, as I will show theoretically and numerically.
[INMA] 2018-12-18 (14:00) : Computation of the maximal invariant set of discrete-time systems with quasi-smooth nonlinear constraints
At Euler building (room A.002)
Speaker :
Zheming Wang (UCLouvain)
Abstract :
Invariant set theory is an important tool for stability analysis and control design of constrained dynamical systems and it has been successfully used to solve various problems in system and control. In this talk, we study the computation of the maximal invariant set of linear systems with a class of nonlinear constraints that has quadratic relaxations. With these quadratic relaxations, we are able to determine a sufficient condition for the maximal invariant set. By using the sufficient condition, we propose an algorithm to compute the exact maximal invariant set. At each iteration, we will solve a set of linear matrix inequalities instead of a nonlinear optimization problem. Thanks to this feature, the proposed algorithm is computationally tractable and efficient in many cases. Under mild assumptions, the proposed algorithm will terminate in finite time. This algorithm can also be extended to a class of nonlinear systems that admit a state feedback linearization. The performance of this algorithm is demonstrated on several numerical examples.
[INMA] 2018-12-12 (16:30) : Predictive Dispatch and Demand Response for Commercial Buildings
At Euler building (room A.002)
Speaker :
Colin Jones (EPFL)
Abstract :
Note the unusual day (Wednesday).
Commercial buildings have significant flexibility in how and when they consume energy, and this freedom can be put to good use by grid operators managing the stability of the grid. This talk will discuss demand response for buildings, or the throttling of power consumption in reaction to signals sent by the grid operator. By shifting energy consumption in time, these techniques can be seen as utilizing the thermal inertia of buildings as a form of virtual electrical storage. In the first part of the talk, we will introduce and analyse a hybrid storage system that combines the best properties of electrical batteries, commercial buildings and generation re-scheduling to better provide balancing services at multiple time scales. We will then demonstrate the effectiveness of the proposed control framework via a set of 12 full day experimental results on the 20kV distribution feeder of the EPFL campus that is comprised of: a set of five uncontrollable office buildings (350kWp) and a roof-top PV installation (90kWp), and a set of controllable resources: a grid-connected BESS (720kVA-500kWh), and a small occupied office building (45 kWp).
[INMA] 2018-12-04 (14:00) : Two 20-minute talks
At Euler building (room A.002)
Speaker :
Guillaume Berger (UCLouvain)
,
and
Legat, Benoît
Abstract :
Speaker: Guillaume Berger
Title: Path-complete p-dominant switching linear systems
Abstract: In this presentation, we study the asymptotic properties of a class of dynamical systems called switched linear systems. Therefore, we introduce the notion of path-complete $p$-dominance for switched linear systems as a way to generalize the notion of dominant/slow modes for LTI systems. Path-dominance is characterized by the contraction property of a set of quadratic cones in the state space. We show that path-dominant systems have a low-dimensional asymptotic behavior, and hence allow for a simplified analysis of their dynamics. Finally, we present an algorithm for deciding the path-dominance of a given system.
Speaker: Benoît Legat
Title: Minimally Constrained Stable Switched Systems and Application to Co-simulation
Abstract: We propose an algorithm to restrict the switching signals of a constrained switched system in order to guarantee its stability, while at the same time attempting to keep the largest possible set of allowed switching signals.
Our work is motivated by co-simulation of complex dynamical systems by multiple cores. There, numerical stability is a hard constraint, but should be attained by restricting as few as possible the allowed behaviours of the simulators.
We apply our results to certify the stability of an adaptive co-simulation orchestration algorithm, which selects the optimal switching signal at run-time, as a function of (varying) performance and accuracy requirements.
[INMA] 2018-11-27 (14:00) : An introduction to sub-Riemannian geometry in SE(2) for vessel analysis and roto-translation equivariant deep learning
At Euler building (room A.002)
Speaker :
B. Erik Ydstie (Carnegie Mellon University
)
Abstract :
This presentation focusses on the application of sub-Riemannian geometry and group theory in 2D medical image analysis. In the discussed image analysis applications, 2D images are lifted to 3D functions on the coupled space of positions and orientations. Lifting is done via a (learned) wavelet-type transformation, leading to a neat organization of image data based on position and orientation. In the extended domain, which we identify with the Lie group SE(2), a sub-Riemannian (SR) geometry is recognized. Here, "sub" refers to the restriction that tangent vectors of naturally lifted curves are contained in a sub-space of the full tangent space. A parallel can be drawn between these curves and the paths of moving cars: a car can only move forward and change direction (2 controls) in a 3D state-space (2D position and orientation), but is not able to move sideways.
In this presentation the following items are discussed:
- A introduction to the Lie group SE(2) (group product, algebra, exponential/logarithmic map and representations)
- An explanation of the sub-Riemannian geometry on SE(2)
- The benefit of using sub-Riemannian geometry for vessel tracking
- The benefit of using the Lie group structure of SE(2) for equivariant or invariant deep learning
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