All Years Seminars
[INMA] 2015-09-22 (11.00) : Two talks on mathematical programming
At Euler building (A002)
Speaker :
Bruno Scherrer (Université de Lorraine and Aarhus University)
,
and
Thomas Dueholm Hansen (Université de Lorraine and Aarhus University)
Abstract : The talk by Bruno Scherrer is entitled "On the use of Non-stationary policies for infinite-horizon Markov Decision Processes", with the following abstract:
I shall consider infinite-horizon $\gamma$discounted Markov Decision Processes, for which it is known that there exists a stationary optimal policy. I will focus on the situation where the problem is so large that only an approximate form of dynamic programming can be implemented. Approximate versions of Value and Policy Iteration, that make an error $\epsilon$ at each iteration, are known to have an asymptotic performance guarantee of $2\gamma\epsilon/(1-\gamma)^2$. After arguing that this bound is tight, I will describe modifications of these algorithms generating non-stationary policies, that allow to improve the performance guarantee by a factor $(1-\gamma)$, which is particularly significant in the typical situation where $\gamma$ is close to 1. A surprising consequence of this result is that the problem of ''computing an approximately optimal non-stationary policy'' is much simpler than that of ''computing an approximately optimal stationary policy''.
Thomas D Hansen will talk about "An improved version of the Random-Facet pivoting rule for the simplex algorithm"
The Random-Facet pivoting rule of Kalai and of Matousek, Sharir, and Welzl is an elegant, randomized pivoting rule for the simplex algorithm, the classical combinatorial algorithm for solving linear programs. The expected running time of the simplex algorithm when using this rule is subexponential in the combinatorial size--the number of variables and inequalities--of the linear program. This is currently the best known combinatorial bound for solving general linear programs. Other polynomial time algorithms are known, but their running time depends also on the number of bits in the representation of the linear program.
We present a slightly improved version of the Random-Facet pivoting rule, thus obtaining the fastest known combinatorial algorithm for solving linear programs, the first improvement in over 20 years. Our results apply not only to linear programs, but also to more general, abstract LP-type problems. In particular we also obtain the fastest known algorithm for solving two-player turn-based stochastic games.
Joint work with Uri Zwick. End of the seminar around noon.
[INMA] 2015-07-16 (14.00) : Towards a Lyapunov framework for Homogeneous and Discontinuous Systems
At Euler building (A002)
Speaker :
Jaime Moreno (UNAM, Mexico)
Abstract : Higher Order Sliding Mode (HOSM) Control is an important tool for robust control of uncertain systems, and it has become a mature field. HOSM control systems and observers
are discontinuous and usually designed to be homogeneous. However, in contrast to many other nonlinear control techniques, a Lyapunov framework for analysis and design
is missing for HOSMs and more generally for homogeneous (possibly) discontinuous systems. Recently, there are important research activities to fill in this gap trying to
provide such a Lyapunov framework. In this talk I will give some attempts and advances obtained by our group in this direction.
[INMA] 2015-07-09 (14.00) : On cooperating automated vehicles for future intelligent transportation systems
At Euler building (A002)
Speaker :
Henk Wymeersch (Chalmers University)
Abstract : For intelligent transportation systems (ITS) to achieve situational awareness beyond their sensing horizon and to harness coordination capabilities,
some form of cooperation will be required. Such cooperation is enabled by vehicle-to-vehicle and vehicle-to-infrastructure wireless communication.
The integration between the communication, signal processing, and control sub-systems is non-trivial and requires a co-design, which in turn requires collaboration
between these three disciplines. We will present a possible evolution of these three disciplines within the context of ITS, as well as several challenges and opportunities.
The speaker will then briefly discuss the two following topics: (i) On the use of graphical models for receiver design in fiber optical communications
(ii) On the fundamental trade-off between accuracy and delay in UWB positioning.
[INMA] 2015-06-23 (14.00) : The Linear project residential demand response put into practice
At Euler building (A002)
Speaker :
Koen Vanthournout (VITO Flemish Institute for Technological Research)
Abstract : Linear was a residential demand response project in Flanders (2009-2014), which evaluated a wide array of smart appliances, 4 demand response business cases
and 2 end user remuneration models together with 240 participating families. Well present an overview of the project and then delve into the details of the four demand
response business cases: intra-day (wind) balancing, day ahead BRP portfolio management, local line voltage control and transformer aging optimization. The control algorithms
deployed will be described and the pilot results presented. Some time will be reserved to discuss a few other topics, selected in situ by the audience to the talk: user
behavior, the ICT architecture, the smart appliances, flexibility potential, practical aspects and lessons learned, etc.
[INMA] 2015-06-18 (14.00) : Differential Equations Models in Biosciences and Reliable Numerics
At Euler building (A002)
Speaker :
Jean M-S Lubuma (University of Pretoria)
Abstract : Biological processes that arise in science are very complex. A lot of effort has been and is being made to build differential equations based models
that aim at elucidating these phenomena. However, these equations cannot be completely solved by analytic techniques. Consequently, reliable numerical simulations
are of fundamental importance in gaining some useful insights on the solutions of the continuous models. Of paramount importance for the involved dynamical systems,
is the design of numerical methods that, apart from being convergent, replicate their underlying dynamics such as the positivity of solutions, the dissipativity of
the systems, the conservation laws, and the stability of equilibria. In this talk, we construct, analyse and implement Nonstandard Finite Difference (NSFD) Schemes
for some deterministic models defined by ordinary and partial differential equations. The NSFD schemes are reliable in three directions. They are topologically
dynamically consistent for one-dimensional models. They replicate the global asymptotic stability of the disease-free equilibrium of compartmental models in epidemiology
whenever the associated threshold quantity is less than unity. They preserve the positivity and boundedness of solutions of reaction-diffusion equations of Fisher-KPP
(Kolmogorov, Petrovsky, Piscounoff) type as well as of cross-diffusion equations that arise in the modelling of cancer growth and predator-prey pursuit-evasion interactions.
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