2015


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Mardi 3 Février
Heure: 14:00 - 17:00
Lieu: Salle B107, bâtiment B, Université de Villetaneuse
Résumé: Graph polynomials and relations with physics
Description: Adrian Tanasa In the first part of the talk I will introduce the Tuttepolynomial of graphs and explicitly show its relation withpolynomials appearing in the so-called parametric representation ofintegrands canonically associated to graphs in quantum field theory.In the second part of the talk I will show a new proof of thecelebrated property of universality of the Tutte polynomial of graphs(or matroids), proof which does not require the usual edge inductionarguments. Finally, I will present how this proof generalizes for theuniversality property of the Bollobas-Riordan polynomial of ribbongraphs (or embedded graphs).
Mardi 10 Février
Heure: 14:00 - 17:00
Lieu: Salle B107, bâtiment B, Université de Villetaneuse
Résumé: Énumérer les cartes farcies de toute topologie (avec un soupçon de combinatoire analytique)
Description: Gaëtan Borot Les cartes sont des surfaces discrètes construites en recollant lelong de leurs bords des polygônes - l'exemple le plus simple étant lestriangulations. En tant que surfaces orientables, leur topologie estcaractérisée par le nombre de bords n, et le nombre d'anses g. Si l'onse donne un poids de Boltzmann t_k pour chaque k-gone, l'énumérationdes cartes à un bord et de genre 0 est un problème très bien étudié.Ici, je considèrerai le problème plus général d'énumérer les cartesfarcies: ce sont les surfaces obtenues en a) piochant dans une boîte àoutils pouvant contenir des surfaces à bords polygonaux et detopologie quelconque ; b) en recollant ces morceaux élémentaires lelong de leurs bords ; c) pondérant l'énumération par des poids deBoltzmann dépendant du genre et de la longueur des bords de chaquemorceau élémentaire. J'expliquerai notamment qu'il existe unerécurrence universelle sur la caractéristique d'Euler totale 2 - 2g -n, qui réduit le problème d'énumération en toute topologie à celui desdisques (n = 1, g = 0) et des cylindres (n = 2,g = 0).
Vendredi 13 Février
Heure: 11:30 - 12:30
Lieu: Salle B107, bâtiment B, Université de Villetaneuse
Résumé: Model checking en logique de dépendance
Description: Nicolas de Rugy-Altherre La logique de dépendance et ses variantes (indépendance et inclusion) ont été introduites par Vänäänen il y a quelques années pour parler de façon "propre" de dépendance en logique. Je présenterai cette logique et ses résultats principaux en complexité.
Mardi 17 Février
Heure: 14:00 - 17:00
Lieu: Salle B107, bâtiment B, Université de Villetaneuse
Résumé: Problèmes de satisfaction de contraintes et graphes inhomogènes
Description: Élie de Panafieu
Jeudi 19 Février
Heure: 16:00 - 17:00
Lieu: Salle B107, bâtiment B, Université de Villetaneuse
Résumé: Modelling Timed Concurrent Systems Using Activity Diagram Patterns
Description: Étienne André UML is the de facto standard for modelling concurrent systems in the industry.
Activity diagrams allow designers to model workflows or business processes.
Unfortunately, their informal semantics prevents the use of automated verification techniques.
In this paper,
we first propose activity diagram patterns for modelling timed concurrent systems;
we then devise a modular mechanism to compose timed diagram fragments into a UML activity diagram that also allows for refinement, and
we formalise the semantics of our patterns using time Petri nets.
Our approach guides the modeller task% (helping to avoid common mistakes), and allows for automated verification.

Joint work with Christine Choppy and Thierry Noulamo
Vendredi 20 Février
Heure: 11:00 - 12:30
Lieu: Salle B107, bâtiment B, Université de Villetaneuse
Résumé: Coherence spaces for computable analysis
Description: Kazushige Terui Abstract:
There have been two mainstream approaches in
computable analysis: the type-two theory of effectivity (TTE)
and the theory of domain representations. This paper proposes
an intermediary approach based on coherence spaces, which is
as concrete as TTE and as structured as domain theory.

We import various concepts from TTE such as admissibility,
and provide admissible representations for the real line, Euclidean
spaces and function spaces over them. This allows us
to represent, for instance, a real continuous function by a stable
map. A natural question is then what linear maps correspond
to in terms of analysis. Our answer is that they correspond
to uniformly continuous functions. This leads to an internal
expression of Heine's theorem (every continuous function on a
compact interval of the real line is uniformly continuous) as the
existence of a certain map from a stable function space to a linear
function space.

We finally illustrate an application of coherence spaces as a
type system for lambda calculus, which allows us to verify local
properties of real functions.

This is a joint work with Kei Matsumoto.
Mardi 24 Février
Heure: 14:00 - 17:00
Lieu: Salle B107, bâtiment B, Université de Villetaneuse
Résumé: Profile of random trees
Description: Michael Drmota
Mercredi 25 Février
Heure: 14:00 - 17:00
Lieu: Salle B107, bâtiment B, Université de Villetaneuse
Résumé: Quasi-random properties of subsequences of sequences generated by finite automata
Description: Michael Drmota Automatic sequences T(n) are the output sequence of a finite automaton, wherethe input is the q-adic digital representation of n. The most prominent exampleis the Thue-Morse sequence t(n) (that is also the fixed point of the substitution0 -> 01, 1 -> 10). Automatic sequences have been studied in many diff erent contextsfrom combinatorics to algebra, number theory, harmonic analysis, geometryand dynamical systems. For example, they have a linear subword complexity andthey are almost periodic.Since the subword complexity is linear the entropy of the related dynamical system is zero. This also means thatthey do not behave like a random sequence. However, the situation changes drastically whenone uses proper subsequences of automatic sequences, for example the subsequence along primes orsquares. It is conjectured that the resulting sequences are normal sequences so thatthey behave like random sequences (=quasi random sequences).Recently this property was proved (together with C. Mauduit and J. Rivat)for the Thue-Morse sequence along the subsequence of squares - and it turns out that thispropery extends to several other automatic sequences and also to subsequences of the form[n^c], where 1 < c < 4/3. Thus such subsequences of automatic sequences give rise toa completely new class of pseudo random sequences that can be computed very efficiently.
Heure: 14:00 - 15:00
Lieu: Amphi A
Résumé: Quasi-Random Properties of Subsequences of Sequences Generated by Finite Automata
Description: Michael Drmota Automatic sequences T(n) are the output sequence of a finite automaton, where
the input is the q-adic digital representation of n. The most prominent example
is the Thue-Morse sequence t(n) (that is also the fixed point of the substitution
0 -> 01, 1 -> 10). Automatic sequences have been studied in many diff erent contexts
from combinatorics to algebra, number theory, harmonic analysis, geometry
and dynamical systems. For example, they have a linear subword complexity and
they are almost periodic.

Since the subword complexity is linear the entropy of the related dynamical system is zero. This also means that
they do not behave like a random sequence. However, the situation changes drastically when
one uses proper subsequences of automatic sequences, for example the subsequence along primes or
squares. It is conjectured that the resulting sequences are normal sequences so that
they behave like random sequences (=quasi random sequences).
Recently this property was proved (together with C. Mauduit and J. Rivat)
for the Thue-Morse sequence along the subsequence of squares - and it turns out that this
propery extends to several other automatic sequences and also to subsequences of the form
[n^c], where 1 < c < 4/3. Thus such subsequences of automatic sequences give rise to
a completely new class of pseudo random sequences that can be computed very efficiently.
Vendredi 27 Février
Heure: 11:00 - 12:30
Lieu: Salle B107, bâtiment B, Université de Villetaneuse
Résumé: Linear numeral systems
Description: Ian Mackie We take a fresh look at an old problem of representing natural numbers
in the lambda-calculus. Our interest is in finding representations
where we can compute efficiently (and where possible, in constant
time) the following functions: successor, predecessor, addition,
subtraction and test for zero. Surprisingly, we find a solution in the
linear lambda-calculus, where copying and erasing are not permitted.
Lundi 2 Mars
Heure: 14:00 - 17:00
Lieu: Salle B107, bâtiment B, Université de Villetaneuse
Résumé: Open questions on Dynamic Semantic Annotation
Description: Ivan GARRIDO MARQUEZ Semantic annotation provides a powerful advantage for several
applications requiring text analysis. Semantic annotation requires the
presence of a semantic model to link the elements of the text to their
semantic representation. An a priori built ontology requires to be
maintained, adapted and to grow to keep its usefulness. When this update
is made along the annotation process, by exploiting the annotated text
to enrich the model we can discuss a dynamicity of the annotation. We
can identify two processes closely related with this dynamicity, the
knowledge acquisition and the annotation process itself. On this talk we
will try present an overview on this processes and how they have been
approached before.
Mardi 3 Mars
Heure: 14:00 - 17:00
Lieu: Salle B107, bâtiment B, Université de Villetaneuse
Résumé: Généralisation des nombres et polynômes de Bernoulli aux cas multiples
Description: Olivier Bouillot Les nombres et polynômes de Bernoulli sont des objets classiques qui apparaissent respectivement lors du prolongement analytique des fonctions zêta de Riemann et de Hurwitz aux entiers négatifs.En lien avec la généralisation multiple de ces fonctions, les multizêtas et multizêtas de Hurwitz, nous allons généraliser les nombres et polynômes de Bernoulli au cas multiple.Bien qu'il n'y a pas unicité d'une telle généralisation, nous introduirons un exemple explicite et satisfaisant où nombres de propriétés importantes des polynômes de Bernoulli se transmettent au cas multiple.Au passage, cela permet de répondre à une question sur la renormalisation des multizêtas aux entiers négatifs.
Mercredi 4 Mars
Heure: 09:30 - 10:30
Lieu: Salle B107, bâtiment B, Université de Villetaneuse
Résumé: On an Extension of Freeze LTL with Ordered Attributes
Description: Normann Decker We present an extension of Freeze LTL, a temporal logic equipped with registers,
over data words. Each position in a (multi-attributed) data word carries a
letter from a finite alphabet and assigns a data value to a fixed, finite set of
attributes. While reasoning on collections of data values is valuable for
expressing correctness properties of executions of dynamic programs the
satisfiability problem of Freeze LTL is undecidable if more than one register is
available or tuples of data values can be stored and compared arbitrarily. Our
extension therefore allows for specifying a dependency relation on attributes.
These dependencies introduce a restricted, yet flexible way of storing and
comparing collections of attribute values. This new dimension of flexibility is
orthogonal to, e.g., the number of registers or the available temporal
operators. In this setting we characterise precisely the type of dependency
relations that maintain decidability of the logic. To this end, we employ
reductions from and to nested counter systems. Moreover, by a complexity
theoretic characterisations we can show that our extension is strict and induces
a semantic hierarchy of logical fragments.
Vendredi 6 Mars
Heure: 11:00 - 12:30
Lieu: Salle B107, bâtiment B, Université de Villetaneuse
Résumé: The Plotkin's call-by-value lambda-calculus from a linear-logical viewpoint
Description: Giulio Guerrieri We translate the terms of ordinary lambda-calculus into proof-nets
accordingly the Girard's call-by-value "boring'' encoding of intuitionistic
implication A->B = !A-o!B. We show that (1) the Plotkin's call-by-value
beta-reduction is (bi)simulated in proof-nets via cut-elimination; (2)
there is a sequentialization theorem that characterizes all and only the
proof-nets which are translations of some lambda-term; (3) the equivalence
relation on lambda-terms which identifies lambda-terms having the same
translation in proof-nets is the call-by-value counterpart of Regnier's
sigma-equivalence and is not included in Plotkin's call-by-value
beta-equivalence. The semantics of lambda-terms is preserved by our
call-by-value sigma-equivalence.
Adding an oriented version of the call-by-value sigma-rules to the
call-by-value beta-reduction (and keeping the same syntax of ordinary
lambda-calculus) we preserve confluence and we get a call-by-value
operational characterization of solvable and potential valuable terms (this
is not possible in original Plotkin's call-by-value lambda-calculus).
Moreover, we give a semantic characterization of solvable and potential
valuable terms in a relational model, based on Linear Logic, satisfying the
Taylor expansion formula. As a technical tool, we also use a
resource-sensitive calculus in which the elements of the model are
definable.
Lundi 9 Mars
Heure: 14:00 - 15:00
Lieu: Salle B107, bâtiment B, Université de Villetaneuse
Résumé: Sequence Classification Based on Delta-Free Sequential Patterns
Description: Pierre Holat Sequential pattern mining is one of the most studied and challenging tasks in data mining. However, the extension of well-known methods from many other classical patterns to sequences is not a trivial task. This talk presents a study of the notion of delta-freeness for sequences. While this notion has extensively been discussed for itemsets, the work described in this talk is the first to extend it to sequences. In this work, we define an efficient algorithm devoted to the extraction of delta-free sequential patterns. Furthermore, we show the advantage of the delta-free sequences and highlight their importance when building sequence classifiers, and we show how they can be used to address the feature selection problem in statistical classifiers, as well as to build symbolic classifiers which optimizes both accuracy and earliness of predictions.
Mardi 10 Mars
Heure: 12:30 - 13:30
Lieu: Salle B107, bâtiment B, Université de Villetaneuse
Résumé: Multiband Robust Optimization: theory and applications
Description: Fabio D'Andreagiovanni Over the last years, Robust Optimization (RO) has emerged as an effective and efficient
methodology to tackle data uncertainty in real-world optimization problems. RO takes into
account data uncertainty in the shape of hard constraints that restrict the feasible set and
maintain only robust solutions, i.e. solutions that remain feasible even when the values of the
input data change.
In this talk, we provide an overview of our research about theory and applications of RO.
Specifically, we present Multiband Robustness, a new model for RO that we recently
proposed to generalize and refine the classical Gamma-robustness model by Bertsimas and
Sim. The main aim of our new model is to provide a refined representation of arbitrary non-
symmetric distributions of the uncertainty, that are commonly present in real-world
applications. Such refined representation grants a reduction in conservatism of robust
solutions, while maintaining the accessibility and computational tractability that have been a
key factor of success of Gamma-robustness. We also provide an overview of applications of
the Multiband model to real-world problems that we have considered in past and ongoing
research and industrial projects.
Heure: 14:00 - 17:00
Lieu: Salle B107, bâtiment B, Université de Villetaneuse
Résumé: Une généralisation des mots de Christoffel en dimension d.
Description: Sébastien Labbé In this work, we extend the definition of Christoffel words todirected subgraphs of the hypercubic lattice in arbitrary dimensionthat wecall Christoffel graphs. Christoffel graphs when $d=2$ correspond towell-known Christoffel words.We show that Christoffel graphs have similar properties to those ofChristoffel words: symmetry of their central part and conjugation withtheirreversal. Our main result extends Pirillo's theorem (characterization ofChristoffel words which asserts that a word $amb$ is a Christoffelword if andonly if it is conjugate to $bma$) in arbitrary dimension.In the generalization, the map $ambmapsto bma$ is seen as a flipoperation ongraphs embedded in $mathbb{Z}^d$ and the conjugation is a translation.We show that a fully periodic subgraph of the hypercubic lattice is atranslate of its flip if and only if it is a Christoffel graph.This is joint work with Christophe Reutenauer.Preprint is available at http://arxiv.org/abs/1404.4021.
Jeudi 12 Mars
Heure: 12:15 - 13:30
Lieu: Salle B107, bâtiment B, Université de Villetaneuse
Résumé: Extraction de motifs graduels pour le résumé de données numériques
Description: Amal Oudni Les résumés linguistiques constituent une représentation linguistique décrivant
un ensemble de données numériques en phrases simples, compréhensibles et facilement interprétables.
Cet exposé se concentre sur les résumés linguistiques sous une forme particulière,
appelée motifs graduels, exprimant des corrélations de co-variations des valeurs
des attributs : on peut les illustrer pa r un exemple du type « plus l'âge du père
est avancé à la naissance des enfants, plus le risque d'autisme chez les enfants augmente ».

Lors de mon exposé, je présenterai trois types de contextualisation de ces motifs graduels.
Dans un premier temps, je décrirai le problème de motifs graduels contradictoires et une
nouvelle approche permettant d’éviter toute ambiguïté entre motifs validés.
Je présenterai ensuite la caractérisation des motifs graduels qui permet de faciliter
l'interprétation des motifs générés en grand nombre en introduisant une nouvelle clause
linguistiquement introduite par l'expression « surtout si ».
Je terminerai par la présentation d’une contextualisation qualifiant le mode de dépendances
graduelles, en introduisant la notion d'accélération par rapport aux autres attributs.

Pour chacune des formes de motifs enrichis extraits, je présenterai une formalisation
de la sémantique et l'interprétation souhaitées, des mesures de qualité pour évaluer
et quantifier la validité des motifs proposés, ainsi que des algorithmes efficaces
d'extraction automatique de ces motifs maximisant les critères de qualité définis.
Heure: 16:00 - 17:00
Lieu: Salle B107, bâtiment B, Université de Villetaneuse
Résumé: Building Bridges Between Sets of Partial Orders
Description: Hernán Ponce de León Partial orders are a fundamental mathematical structure capable of representing concurrency and causality on a set of atomic events. In many applications it is essential to consider multiple partial orders, each representing a particular behavioral scenario or an operating mode of a modeled system.

In this talk I will present two mathematical formalisms capable of the compressed representation of sets of partial orders: Labeled Event Structures (LESs) and Conditional Partial Order Graphs (CPOGs). I will demonstrate their advantages and disadvantages and propose efficient algorithms for transforming of a set of partial orders from a given compressed representation in one formalism into an equivalent representation in another formalism without the explicit enumeration of each scenario. These algorithms make use of an intermediate mathematical formalism, which we call Conditional Labeled Event Structures (CLESs), that combines the advantages of LESs and CPOGs.

This is joint work with Andrey Mokhov (Newcastle University)
Vendredi 13 Mars
Heure: 11:00 - 12:30
Lieu: Salle B107, bâtiment B, Université de Villetaneuse
Résumé: Functors are Type Refinement Systems
Description: Noam Zeilberger The standard reading of type theory through the lens of category
theory is based on the idea of viewing a type system as a category of
well-typed terms. In this joint work with Paul-André Melliès we propose a basic revision of this reading: rather
than interpreting type systems as categories, we describe them as
functors from a category of typing derivations to a category of
underlying terms. Then, turning this around, we explain how in fact
*any* functor gives rise to a generalized type system, with an
abstract notion of typing judgment, typing derivations and typing
rules. This leads to a purely categorical reformulation of various
natural classes of type systems as natural classes of functors.

In the talk I want to motivate and introduce this general framework
(which can also be seen as providing a categorical analysis of
_refinement types_), and as a larger example give a sketch of how the
framework can be used to formalize an elegant proof of a coherence
theorem by John Reynolds. If time permits, I will also describe some
of the natural questions raised by this perspective that are the
subject of ongoing research.
Mardi 17 Mars
Heure: 14:00 - 17:00
Lieu: Salle B107, bâtiment B, Université de Villetaneuse
Résumé: ALEA, au CIRM (16-20 mars)
Description: Journées ALEA
Jeudi 19 Mars
Heure: 12:15 - 13:30
Lieu: Salle B107, bâtiment B, Université de Villetaneuse
Résumé: Calcul efficace de la stabilité des concepts formels
Description: Sadok BEN YAHIA Dans l'ère des données massives, l'alliance de la qualité avec l'efficience pour la sélection des concepts formels « intéressants » serait une condition sine qua non. Dans ce cadre, la mesure de stabilité, de concepts formels, indiquerait dans quelle mesure l'intension de ce concept est liée à la présence d'objets particuliers dans son extension. Un concept stable possède, ainsi, une existence d'autant plus « réelle » que son intension ne dérive pas fortuitement d'une description bruitée de ses objets. Ainsi, les concepts stables sont très intéressants à localiser dans beaucoup de domaines puisqu'ils sont résistants au bruit, e.g., détection de communautés stables, classification par des classes monothétiques/ polythétiques.

Cependant, le calcul de la stabilité serait très couteux, ie., exponentiel en fonction de la taille de l'extension du concept. En effet, il faudrait explorer l'espace de tous les sous-ensembles de l'extension à la recherche qui restent fidèles à l'intension du concept formel.

Dans ce séminaire, nous passons en revue les très peu nombreux travaux qui se sont intéressés au calcul de la stabilité des concepts formels (organisés sous forme de treillis ou non). Ensuite, nous présentons des travaux récents sur l'exploitation des propriétés de monotonie et d'anti-monotonies des éléments clés dans l'espace de recherche. Ainsi, la saturation des cliques maximales non génératrices permet de traiter des espaces avoisinant les 215000. Nous montrons aussi que les identités d'inclusion/ exclusion servent au calcul efficace des stabilités des concepts formels organisés sous la forme d'un treillis.
Heure: 14:30 - 15:30
Lieu: Salle B107, bâtiment B, Université de Villetaneuse
Résumé: Effective verification of low-level software with nested interrupts
Description: Lihao Liang Interrupt-driven software is difficult to test and debug, especially when
interrupts can be nested and subject to priorities. Interrupts can arrive
at arbitrary times, leading to an explosion in the number of cases to be
considered. We present a new formal approach to verifying interrupt-driven
software based on symbolic execution. The approach leverages recent
advances in the encoding of the execution traces of interacting, concurrent
threads. We assess the performance of our method on benchmarks drawn from
embedded systems code and device drivers, and experimentally compare it to
conventional formal approaches that use source-to-source transformations.
Our experimental results show that our method significantly outperforms
conventional techniques. To the best of our knowledge, our technique is the
first to demonstrate effective formal verification of low-level embedded
software with nested interrupts.

Joint work with
Daniel Kroening, Tom Melham, Peter Schrammel and Michael Tautschnig
Vendredi 20 Mars
Heure: 11:00 - 12:30
Lieu: Salle B107, bâtiment B, Université de Villetaneuse
Résumé: An infinitary model of linear logic
Description: Charles Grellois We construct an infinitary variant of the relational model of linear logic, where the exponential modality is interpreted as the set of finite or countable multisets. We explain how to interpret in this model the fixpoint operator Y as a Conway operator alternatively defined in an inductive or a coinductive way. We then extend the relational semantics with a notion of color or priority in the sense of parity games. This extension enables us to define a new fixpoint operator Y combining both inductive and coinductive policies. We conclude by sketching the connection between the resulting model of lambda-calculus with recursion and higher-order model-checking.
Mardi 24 Mars
Heure: 12:30 - 13:30
Lieu: Salle B107, bâtiment B, Université de Villetaneuse
Résumé: Unit Commitment problems: approaches and solution algorithms
Description: Claudio Gentile The Unit Commitment is a the problem to manage a set of power generating units of different types over a short time horizon.
Unit Commitment is formulated as a Mixed Integer Nonlinear Programming problem. It requires special techniques to handle both the large size of the instances to be solved and the nonlinearity of the objective function.
Two main approaches have been used in its solution: the Lagrangian Relaxation coupled with primal heuristics and MILP approximations. We discuss some new advancements for both approaches.
Heure: 14:00 - 17:00
Lieu: Salle B107, bâtiment B, Université de Villetaneuse
Résumé: Automates d'arbres
Description: Gwendal Collet
Mercredi 25 Mars
Heure: 14:00 - 15:00
Lieu: Amphi A
Résumé: Extending Petri Nets with Object-Orientation
Description: Charles Lakos This seminar will introduce the formalism of Petri Nets and their use in modelling and analysing concurrent systems. It will briefly mention some of the extensions of Petri Nets to achieve greater descriptive comfort. It will then report on work over a number of years to extend Petri Nets with Object-Oriented features, thereby making it easier to define polymorphic modules and to capture incremental development. The seminar will also describe the properties of such nets and the analysis possibilities.
Mardi 31 Mars
Heure: 14:00 - 17:00
Lieu: Salle B107, bâtiment B, Université de Villetaneuse
Résumé: TASEP
Description: Erik Aas
Jeudi 2 Avril
Heure: 12:15 - 13:30
Lieu: Salle B107, bâtiment B, Université de Villetaneuse
Résumé: Extraction non supervisée de classes évolutives à partir de données temporelles
Description: Allou Samé La classification de données évoluant au cours du temps constitue une problématique centrale dans de nombreuses applications. Dans ce cadre, les paramètres des classes doivent pouvoir s’adapter à l’évolution potentiellement non stationnaire des données. Cet exposé montrera comment les mélanges de lois peuvent être exploités, conjointement avec les modèles à espace d’état (filtre de Kalman), pour atteindre cet objectif. Partant de ce formalisme, un algorithme EM variationnel et sa version online seront détaillés. Ceux-ci seront illustrés sur des données simulées et des données réelles dans le cadre d’un problème de diagnostic dans le secteur ferroviaire.
Mardi 7 Avril
Heure: 14:00 - 17:00
Lieu: Salle B107, bâtiment B, Université de Villetaneuse
Résumé: Structure algébrique des opérateurs de Fliess.
Description: Loïc Foissy
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
Jeudi 9 Avril
Heure: 14:30 - 15:30
Lieu: Salle B107, bâtiment B, Université de Villetaneuse
Résumé: Enhanced Distributed Behavioral Cartography of Parametric Timed Automata
Description: Hoang Gia Nguyen Parametric timed automata (PTA) allow the specification and verification of timed systems incompletely specified, or subject to future changes. The behavioral cartography splits the parameter space of PTA in tiles in which the discrete behavior is uniform. Applications include the optimization of timing constants, and the measure of the system robustness w.r.t. the untimed language. Here, we present enhanced distributed master-worker algorithms to compute the cartography efficiently. Experimental results show that our new algorithms significantly outperform previous distribution techniques.
Mardi 14 Avril
Heure: 14:00 - 17:00
Lieu: Salle B107, bâtiment B, Université de Villetaneuse
Résumé: Diamètre et hamiltonicité des associaèdres de graphe
Jeudi 16 Avril
Heure: 14:30 - 15:30
Lieu: Salle B107, bâtiment B, Université de Villetaneuse
Résumé: "Formalising Concurrent UML State Machines Using Coloured Petri Nets"
Description: Mohamed Mahdi Benmoussa While UML state machines are widely used to specify dynamic systems behaviours, their semantics is described informally, which prevents the complex systems verification.
In this paper, we propose a formalisation of concurrent UML state machines using coloured Petri nets.
We consider in particular concurrent aspects (orthogonal regions, forks, joins, shared variables), the hierarchy induced by composite states and their associated activities, internal/external/local transitions, and entry/exit/do behaviours.
Vendredi 17 Avril
Heure: 11:00 - 12:30
Lieu: Salle B107, bâtiment B, Université de Villetaneuse
Résumé: gdt Homotopy Type Theory - séance 1
Description: Andrew Polonsky The first of a little series of talks on Homotopy Type Theory (i.e., higher-order algebraic treatment of the notion of equality in dependant type theory).

Logical relations are a technique for proving meta-theoretic
properties of type systems.
In recent years, they have received a lot of attention as it became
clear that logical relations give the most natural definition of
extensional equality in type theory.
A major open problem is to define a type system which contains
extensional equality as an internal type constructor. For this, it is
necessary to reflect the external logical relation back into the
syntax of the type language.
In this talk I will describe how to do this.
Mardi 21 Avril
Heure: 14:00 - 17:00
Lieu: Salle B107, bâtiment B, Université de Villetaneuse
Résumé: La tour de Hanoï, revue par Dudeney
Description: Thierry Bousch Dans la version classique de "la Tour de Hanoï", c'est-à-direavec trois aiguilles, on sait bien qu'on peut transférer N disquesd'une aiguille vers une autre en 2^N-1 mouvements, et que ce nombreest minimal. Ajoutons une quatrième aiguille: quel est alors le nombreminimum de mouvements nécessaires pour transférer N disques d'uneaiguille vers une autre? Etrangement, ce problème posé il y a plusd'un siècle par le puzzliste anglais Henry Ernest Dudeney n'a étérésolu que tout récemment. Et pour d'autres variantes de la Tourde Hanoï, avec davantage d'aiguilles ou des restrictions sur lesmouvements, le problème est largement ouvert.voir aussi l'article sur le site du CNRS
Mardi 28 Avril
Heure: 12:30 - 13:30
Lieu: Salle B107, bâtiment B, Université de Villetaneuse
Résumé: Exact Algorithms for Nonconvex Quadratic Integer Optimization
Description: Christoph Buchheim The talk addresses the problem of minimizing a quadratic objective function over integer variables. Even in the most simple case of binary or box-constrained integer variables, such problems are very hard to solve in theory and in practice. In fact, the problem remains NP-hard both in the case of a convex objective function over binary variables (then being equivalent to max-cut) and in the case of a non-convex objective function over the unit cube (the so-called BoxQP).

After shortly reviewing some classical approaches for quadratic discrete optimization, we present two recent methods that are specifically designed for the nonconvex case, aiming at relaxations that jointly address the nonconvexity of the objective function and the nonconvexity of the discrete variable domains. While the first approach results in a semidefinite relaxation of the problem, the second approach uses ellipsoidal relaxations; both approaches can be embedded into branch-and-bound schemes. We present experimental results for the resulting algorithms, showing that the SDP-based approach yields very strong dual bounds that however take more time to be computed, while the second approach based on ellipsoidal relaxations is able to enumerate a large number of nodes in a short time due to a sophisticated preprocessing phase. The resulting total running times are comparable; both approaches however significantly outperform standard software such as Couenne or BARON.