Avviso di seminari

24/01/08

ore 15-16 Prof. Dr. Gert Wanka, Chemnitz University of Technology, Chemnitz, Germany: "Closedness Type and Subdifferential Regularity Conditions for Conjugate Duality in Infinite Dimensional Spaces".

ore 16-16.30 coffee break

ore 16.30-17.30 Prof. Dr. Radu Ioan Bot, Chemnitz University of Technology, Chemnitz, Germany: "On an open problem regarding totally Fenchel unstable functions".

Approfitto dell'occasione per chiederle anche di diffondere notizia di altri due seminari che si terranno presso il Dipartimento di Matematica Applicata "U.Dini" il 30/01/08.

30/01/08

ore 10-11 Prof. Immanuel M. Bomze, University of Vienna: " On the road to tractability: from combinatorial optimization via copositive programming to SDP-based approximation".

Abstract:

Quite many combinatorial and some important non-convex continuous optimization problems admit a copositive representation, where the complexity of solving non-convex programs is shifted towards the complexity of sheer feasibility.

Using characterizations of copositivity, one arrives at various SDP-based approximations. However, not all of these are tractable with current technology. This talk addresses some approaches on which tractable semidefinite-programming (SDP) approximations may be based, along with specific strategies to generate interesting test instances of intermediate complexity.

ore 11-11.30 coffee break

ore 11.30-12.30 Prof. Fabio Schoen, Università di Firenze: "Practical Global Optimization: from the Circle Packing Contest to Binary Atomic Clusters and beyond".

Abstract:

In this talk we will review some recent computational results in large scale global optimization. Starting from the techniques we used and which led our group to win the Circle Packing Contest (http://www.recmath.org/contest/CirclePacking) we will explain how that experience proved itself extremely useful in a quite different context, that of finding the global minimum energy configuration of atomic clusters composed by atoms of two different types. Differently from classical (e.g. Lennard-Jones or Morse) potential energy optimization, for the optimization of binary clusters the combinatorial nature of the problem has to be taken into account. In fact, once the coordinates of N atoms have been decided, through the minimization of a smooth function, exponentially many isomers can be defined, by assigning different atom types to different locations (some sort of a 3-dimensional anagram). We will present our quite simple strategy which led us to find improved configuration for at least 90 of the previously known putative optima deposited at the Cambridge Cluster Database. Very recently we tried to apply a similar algorithmic framework to another, quite unrelated, contest: finding the best departure and travel times of a spacecraft which, starting from Earth, should visit some (3) asteroids to be chosen in a known group. The objective was to minimize a function of fuel consumption and of the stay time at each asteroid, with constraints on the maximum length of the mission (less than 10 years). Although quite unexperienced in this field and although the competition ran for only one month, we ranked 10-th out of 23 participants: in the talk we will briefly sketch our approach.

Nel ringraziarla le porgo distinti saluti, Barbara Panicucci.

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