All Years Seminars
[INMA] 2014-09-16 (14.00) : Automatic control and biological systems : a long quiet river?
At Euler building (A207)
Speaker :
Denis Dochain (CESAME)
Abstract : Biology is probably the science of this century, and there is a rapidly growing interest in the system theory community over the past decade. Yet research in the field of the control of biological systems has already a rather long history coming back to the late sixties. The development of efficient monitoring and control tools for biological systems has indeed to face several major difficulties. These include the inherent complexity and variability of the biological systems resulting in models of high complexity that are difficult to validate in absence of sufficient and reliable data. This talk aims at giving an overview of over thirty years of research activities in this field.
[INMA] 2014-08-26 (14.00) : Robust Matrix Decomposition with Fixed-Rank Constraint
At Euler building
Speaker :
Julio Guerrero (Universidad de Murcia, Spain)
Abstract :
There are many applications in which one can find a structured matrix (signal) severely affected by noise and outliers. Due to the presence of noise, when a signal is observed its original structure (e.g., low-rank) is lost, giving rise to a matrix without any apparent property. In many real applications, it is of great interest to be able to decompose such a corrupted matrix into the sum of the original (uncorrupted) low-rank matrix and a residual matrix containing the noise.
A traditional method to recover the low-rank structure of a matrix is Principal Component Analysis (PCA). However, PCA is known to fail in the presence of high levels of noise, leading to wrong estimations. It has been recently discovered that, in those cases where the noise/outliers can be modeled as a sparse component an exact decomposition is possible via a combination of nuclear-norm and l1-norm minimization. Robust PCA is the main representative of this trend, having being successfully applied to a wide variety of problems such as: motion estimation, background subtraction, video surveillance, face recognition, photometric stereo, Robust Manifold Learning, biomedical images, etc. Furthermore, RPCA is intimately related to other relevant problems like robust matrix completion (the Netflix Prize) and matrix sensing.
In our research, we have focused on those cases where the low-rank matrix can be characterized by a fixed rank constraint, usually imposed by the physical constraints of the system under study (e.g., motion estimation, photometric stereo, etc.). In this talk we propose a new method where Robust PCA is adapted to efficiently deal with fixed-rank constraints. Our approach, named FixedRank via Alternating Direction Method (FR-ADM) poses the optimization problem on the manifold of fixed-rank matrices , parametrized as the factor manifold of two Stiefel manifolds and a SPD manifold taken quotient by rotations. We achieved a very efficient optimization through the use of Alternating Direction minimization on the three submanifolds, using closed-form expressions for the projectors onto each submanifold. In particular, for the SPD manifold, we introduce a novel and fast projector and we prove its validity during the minimization process. The resulting method outperforms existing methods in terms of accuracy and speed. Further acceleration can be obtained by using a Nystrom based scheme to achieve linear complexity.
[INMA] 2014-06-17 (14.00) : Cyber-Secure Control: Challenges and Quantification
At Euler building
Speaker :
Sandberg, Henrik
Abstract :
Cyber-attacks on critical infrastructures, such as power networks, are a growing concern in society and have received considerable media attention lately. In this talk, we therefore discuss possible implications for networked control systems under such malicious attacks. We introduce an adversary modeling framework and use it for quantifying cyber security of control systems by means of constrained optimization problems. These optimization problems help to quantify trade-offs between attack impact on control performance, attack detectability, and adversarial resources. The first illustrating example concerns Supervisory Control and Data Acquisition (SCADA) systems for electric power networks. We both illustrate how the trade-off analysis can be done efficiently using minimum-cut algorithms for graphs, and how to use the outcome for allocation of limited protection resources. In the second illustrating example, we quantify cyber security in a wireless control system for a quadruple-tank process.
[INMA] 2014-05-20 (14.00) : The Global Grid
At Euler building
Speaker :
Damien Ernst (ULg)
Abstract :
In this talk, Damien Ernst will discuss the future of our electricity networks. He will explain through simple but rigorous
arguments that in the near future, the race for renewable energy will cause the interconnection of electricity grids of
the planet. They will form one single electrical grid - called The Global Grid - linking together the vast majority of
consumers and electricity producers in the world.
With The Global Grid, the electrical commodity will be exchanged internationally as it is the case now with oil or coal.
Professor Ernst will also address the dangers associated with the globalization of the electric commodity, and the many
challenges that Belgium and its electric industry will face in this global context.
[INMA] 2014-05-13 (14.00) : Analytic interpolation and experiment design in system identification
At Euler building
Speaker :
Kaushik Mahata (University of Newcastle, Australia)
Abstract :
We investigate how the variance error associated with the prediction
error identification is related to the power spectral densities of the input and the
additive noise at the output. We characterize the set of all input and noise power
spectral densities for which the variance error remains constant. This analysis
results a minimal, finite-dimensional, affine parameterization of the variance error.
This parameterization connects our analysis with the theory of Nevanlinna-Pick
interpolation. It is shown that the set of all PSDs for which the variance error
remains constant can be characterized by the solutions of a Nevanlinna-Pick
interpolation problem. This insight has interesting consequences in optimal input
design, where it is possible to use some recent tools in analytic interpolation theory
to tune shape of the input PSD to suit certain needs.
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