All Years Seminars
[INMA] 2007-10-23 (14.00) : "Adaptive optimization techniques for control and estimation"
At Euler building
Speaker :
Martin GUAY
( Queen's University, Canada)
Abstract :
In this talk, we will provide an overview of recent advances in real-time optimization techniques
for application in control and estimation. We focus on specific contributions in the area of adaptive
optimizing control for extremum-seeking control and model predictive control. We will show how these
techniques can be used to tackle a wide range of control problems for highly uncertain, nonlinear systems
subject to constraints that cannot be handled with existing techniques.
[INMA] 2007-10-16 (14.00) : "An efficient algorithm for large-scale linear and convex optimization in relative scale"
At Euler building
Speaker :
Peter RICHTARIK
( Cornell University
)
Abstract :
We propose two variants of a single efficient O(1/epsilon) algorithm simultaneously solving a
number of related optimization problems in relative scale:
1 )Find the intersection of a line and a centrally symmetric convex body Q given as the convex hull of a collection of points.
Interpretation: Our method produces a sequence of ellipsoids inscribed in Q, and ``converging" towards the
intersection points and as such can be viewed as a modification of the ellipsoid rounding algorithm of Khachiyan.
2) Maximize a linear function over the polytope polar to Q.
Interpretation: A "variant" of the ellipsoid method of Nemirovski-Yudin-Shor.
3) Find the minimum l1 norm solution of a full rank underdetermined linear system.
Interpretation: An Iteratively Reweighted Least Squares (IRLS) method.
4) Minimize the maximum of absolute values of linear functions on a hyperplane.
Interpretation: Shor's subgradient method with space dilation.
5)Minimize a (special) smooth convex function on the unit simplex.
Interpretation: A version of the Frank-Wolfe method with specialized line search.
From among the many possible applications we outline those to truss topology design and optimal design of
statistical experiments.
[INMA] 2007-10-09 (14.00) : "Transforming visual signals into accurate 3D reach plans"
At Euler building
Speaker :
Blohm, Gunnar
Abstract :
Most of our interactions with objects surrounding us are guided by vision.
My research investigates how visual information about a desired reach target
is translated into a geometrically accurate 3D motor plan for the arm. To answer
this question, I used three different approaches. First, I built a geometrical model
which theoretically describes how extra-retinal eye and head position signals (or their absence)
affect this visuomotor transformation. Specific predictions from this model were compared to
behavioral human reaching performance, and revealed that the normally functioning brain uses
extraretinal signals to transform visual signals into a reach plan. This model is also important in the
analysis and interpretation of patient data where areas of the brain involved in these visuomotor
transformation pathways are damaged. Second, I designed a simple feed-forward neural network
to perform this visuomotor transformation. A detailed analysis of how this artificial neural network
solves the visuomotor conversion shows how the brain could potentially perform this transformation
and predicts which neural properties to look for in the involved brain regions. Finally, I identified neural
structures as well as the timing underlying the visuomotor transformation for reaching in humans using
functional brain imaging (magneto-encephalography). Taken together, these studies show why we need
an explicit visuomotor transformation, how this could be achieved by the brain, which brain structures are
involved in the different aspects and how they dynamically perform this visuomotor transformation from
visual input to the motor output.
[INMA] 2007-10-02 (14.00) : Colloquium CESAME/MAPA "Leonhard Euler : his life, the man, and his work"
At Euler building
Speaker :
Walter GAUTSCHI
(Purdue University
)
Abstract :
On the occasion of the 300th anniversary of Euler's birth (on April
15, 2007), an attempt is made to bring Euler's genius to the attention of a broad segment
of the educated public. The three stations of his life - Basel, St. Petersburg, and Berlin - are sketched
and the principal works identified in more or less chronological order. To convey a flavor of his work and its
impact on modern science, a selection of some of Euler's memorable contributions is made and discussed in
more detail. Remarks on Euler'personality, intellect, and craftsmanship, will round out the lecture.
[INMA] 2007-09-25 (14.00) : "Informative experiments: how to get just sufficiently rich?"
At Euler building
Speaker :
Gevers, Michel
Abstract :
System identification requires informative data, resulting from informative experiments.
Whereas a range of sufficient conditions for informative experiments has been available for a long time,
there were surprisingly no results of necessary and sufficient nature. With the recent surge of interest in
optimal experiment design, whose solutions are typically in the form of multisines, it is of interest to know
the minimum number of multisines required for identifiability. We provide a complete analysis of the minimum
degree of richness required for identifiability for all commonly used model structures, both in open loop and in
closed loop. In a closed-loop setup, where identification can be achieved with no external excitation when the
controller is of sufficient degree, our results provide an unexpected and precisely quantifiable trade-off between
controller degree and required degree of external excitation.
Seminars
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