Mai 2015


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Mardi 5 Mai
Heure: 14:00 - 17:00
Lieu: Salle B107, bâtiment B, Université de Villetaneuse
Résumé: Comptage et énumération de surfaces plates, formes quasimodulaires
Description: Samuel Lelièvre
Jeudi 7 Mai
Heure: 15:00 - 18:00
Lieu: Salle B107, bâtiment B, Université de Villetaneuse
Résumé: Présoutenance de thèse : A left/right dynamic on permutations
Description: Quentin de Mourgues Soit s une permutation dans Sigma_n.Soit i(s)=s(1), j(s)=s^{-1}(1),Soit C_k le cycle 1>2>...>(k-1)>1 (k,k+1,..,n points fixes).On definit L et R comme suit:L(s) = C_{j(s)}.s etR(s) = s.C_{i(s)}^{-1}Il est facile de voir que L et R sont inversibles, la dynamique L/R partitionne donc Sigma_n en classes d'équivalence qui sont des graphes orientés uniformes (une arête entrant/sortant par "couleur" L et R) fortement connexes.Dans cet exposé, on étudiera ces classes : leur nombre, leur taille, leur structure, etc.
Heure: 16:00 - 19:00
Lieu: Salle B107, bâtiment B, Université de Villetaneuse
Résumé: Présoutenance de thèse : Tilings
Description: Alexandra Ugolnikova
Lundi 11 Mai
Heure: 14:00 - 15:00
Lieu: Salle B107, bâtiment B, Université de Villetaneuse
Résumé: Structured Prediction, Optimization and Deep Syntax
Description: Caio Filippo Corro A sequence of words is not a sufficient representation for efficient
processing of natural languages. In order to extract information from
sentences, we need to decode their underlying abstract structure(s).
Unfortunately, grammar formalisms that are able to properly capture
complicated phenomena encountered in natural languages (wh-movements,
cross-serial dependencies,...) have a repelling complexity. The work in
this thesis will focus on developing efficient parsing algorithms for
various formalisms (TAG, LCFRS, RCG) using optimization methods
(Lagrangian relaxation, dual decomposition).
Mardi 12 Mai
Heure: 11:00 - 14:00
Lieu: Salle B107, bâtiment B, Université de Villetaneuse
Résumé: Various aspects of automaton synchronization
Description: Mikhael Berlinkov
Heure: 12:30 - 13:30
Lieu: Salle B107, bâtiment B, Université de Villetaneuse
Résumé: EXACT APPROACHES TO THE NETWORK DESIGN PROBLEM WITH RELAYS
Description: Ivana Ljubic This work considers the Network Design Problem with Relays (NDPR). The
NDPR arises in the context of network design when given node-pairs need
to communicate with each other, but, due to signal deterioration,
communication paths have to respect given distance limits. To cover
longer distances, equipment for signal regeneration (i.e., relays) may
be required. To enable required communications, one has to upgrade the
network: by installing new links, by installing relays on the existing
network, or by a combination of both. Besides applications in network
design, the NDPR arises in the context of e-mobility where relays model
charging stations for electric cars and edge costs correspond to road
tolls.

In contrast to previous work on the NDPR, which was mainly focused on
heuristic approaches, we propose new exact approaches based on different
mixed integer linear programming formulations for the problem. We
develop Branch-and-Price and Branch-Price-and-Cut algorithms that build
upon models with an exponential number of constraints and variables. In
a computational study, we analyze the performance of these approaches
for instances with different characteristics.

This is a joint work with M. Leitner, M. Riedler and M. Ruthmair
Heure: 14:00 - 17:00
Lieu: Salle B107, bâtiment B, Université de Villetaneuse
Résumé: Énumération d'automates minimaux et fonctions de parking
Description: Jean-Baptiste Priez
Mardi 19 Mai
Heure: 12:30 - 13:30
Lieu: Salle B107, bâtiment B, Université de Villetaneuse
Résumé: Approximating the energy storage problem and other continuous dynamic programs
Description: Giacomo Nannicini We study the problem of optimally managing a source of renewable
energy connected to the power grid, a battery, and potentially a
household or some other form of energy sink. This problem can be
naturally cast as a dynamic program. We propose a model for this
problem that subsumes other models in the literature, and we analyze
its complexity, showing that in the deterministic setting the problem
is solvable in polynomial time, but it becomes #P-hard in the
stochastic setting. A variant of the problem that is commonly
encountered in practice (i.e. the one where selling energy to the
power grid is not allowed) admits a Fully Polynomial Time
Approximation Scheme (FPTAS) if the energy levels are discretized;
but what about the more natural case where energy is considered a
continuous variable? We show that in this case, the problem belongs to
a class of convex continuous dynamic programs that admits neither a
multiplicative nor an additive approximation. We then show that we can
construct a novel type of approximation scheme, where additive and
multiplicative approximation are required at the same time but both
can be arbitrarily small. We discuss a preliminary computational
evaluation of this new type of approximation scheme for continuous
convex dynamic programs, showing its potential.
Heure: 14:00 - 17:00
Lieu: Salle B107, bâtiment B, Université de Villetaneuse
Résumé: Explicit forms and combinatorial content of Levy stable distributions
Description: Katarzyna Górska
Jeudi 21 Mai
Heure: 14:30 - 15:30
Lieu: Salle B107, bâtiment B, Université de Villetaneuse
Résumé: Reachability Preservation Based Parameter Synthesis for Timed Automata
Description: Étienne André The synthesis of timing parameters consists in deriving conditions
on the timing constants of a concurrent system such that it meets its
specification.
Parametric timed automata are a powerful formalism for parameter
synthesis, although most problems are undecidable.
We first address here the following reachability preservation
problem: given a reference parameter valuation and a (bad) control
state, do there exist other parameter valuations that reach this control
state iff the reference parameter valuation does?
We show that this problem is undecidable, and introduce a procedure
that outputs a possibly underapproximated answer.
We then show that our procedure can efficiently replace the
behavioral cartography to partition a bounded parameter subspace into
good and bad subparts; furthermore, our procedure can even outperform
the classical bad-state driven parameter synthesis semi-algorithm,
especially when distributed on a cluster.
Mardi 26 Mai
Heure: 14:00 - 17:00
Lieu: Salle B107, bâtiment B, Université de Villetaneuse
Résumé: Efficient Algebraic Diagonals and Walks
Description: Louis Dumont The diagonal of a multivariate power series F is the univariate power series Diag F generated by the diagonal terms of F. Diagonals form an important class of power series; they occur frequently in number theory, theoretical physics and enumerative combinatorics. Westudy algorithmic questions related to diagonals in the case where F is the Taylor expansion of a bivariate rational function. It is classical that in this case Diag F is an algebraic function. We propose an algorithm that computes an annihilating polynomial forDiag F. Generically, it is its minimal polynomial and is obtained in time quasi-linear in its size. We show that this minimal polynomial has an exponential size with respect to the degree of the input rational function. Throughout the talk, we use a common problemof counting certain lattice walks to illustrate the capacities and limits of our tools.
Mercredi 27 Mai
Heure: 14:00 - 16:00
Lieu: Salle B107, bâtiment B, Université de Villetaneuse
Résumé: Logics via algebras and substitutions
Description: Antonino Salibra In this talk we present a translation of formulas and models of classical and non-classical logics
into factor algebras. The correspondence:
Propositional variables --- operator of decompositions
Logical operations --- substitutions
Formulas --- algebraic terms
Models --- factor algebras,
provides a uniform calculus of provability for all the logics which admit the translation.
Many examples will be discussed:
classical logic, intuitionistic logic, linear logic, many-valued logics.