Institut de Recherche en Informatique Fondamentale

IRIF Université Paris 7 CNRS L'IRIF est une unité mixe de recherche (UMR 8243) du CNRS et de l'Université Paris-Diderot, issue de la fusion des deux UMR LIAFA et PPS au 1er janvier 2016.

Ses objectifs scientifiques se déclinent selon trois grandes thématiques au cœur de l'informatique : les fondements mathématiques de l’informatique ; les modèles de calcul et de preuves ; la modélisation, les algorithmes et la conception de systèmes.

Prochains séminaires

Lundi 05 décembre 2016 · 11h00 · Salle 1007

Vérification · Guilhem Jaber (IRIF) · SyTeCi: Symbolic, Temporal and Circular reasoning for automatic proofs of contextual equivalence

Operational Techniques (Kripke Logical Relations and Environmental/Open/Parametric Bisimulations) have matured enough to become now formidable tools to prove contextual equivalence of effectful higher-order programs. However, it is not yet possible to automate such proofs – the problem being of course in general undecidable. In this talk, we will see how to take the best of these techniques to design an automatic procedure which is able many non-trivial examples of equivalence, including most of the examples from the literature. The talk will describe the main ingredients of this method: - Symbolic reduction to evaluate of programs, - Transition systems of heap invariants, as used with Kripke Logical Relations, - Temporal logic to abstract over the control flow between the program and its environment, - Circular proofs to automate the reasoning over recursive functions. Using them, we will see how we can reduce contextual equivalence to the problem of non-reachability in some automatically generated transition systems of invariants.

Mardi 06 décembre 2016 · 11h00 · Salle 1007

Algorithmes et complexité · Omar Fawzi · Algorithmic aspects of optimal channel coding

We study the problem of finding the maximum success probability for transmitting messages over a noisy channel from an algorithmic point of view. In particular, we show that a simple greedy polynomial-time algorithm computes a code achieving a (1-1/e)-approximation of the maximum success probability and that it is NP-hard to obtain an approximation ratio strictly better than (1-1/e). Moreover, the natural linear programming relaxation of this problem corresponds to the Polyanskiy-Poor-Verdú bound, which we also show has a value of at most 1/(1-1/e) times the maximum success probability.

Based on joint work with Siddharth Barman. arXiv:1508.04095

Mardi 06 décembre 2016 · 14h00 · Salle 1007

Algorithmique distribuée et graphes · Carl Feghali (IRIF) · Problems and Results in Kempe Equivalence of Colorings

Given a graph G with a coloring, a Kempe chain of G is a maximal connected subgraph of G in which each vertex has one of two colors. A Kempe change is the operation of swapping the colors of a Kempe chain. Two colorings are Kempe equivalent if one can be obtained from the other by a sequence of Kempe changes. In this talk, we survey some of the existing results, open problems and common proof techniques in this area.

Mardi 06 décembre 2016 · 11h00 · Salle 3052

Sémantique · Yann Régis-Gianas (IRIF) · Explaining Program Differences Using Oracles

Program differences are pervasive in software development, but most of the time they are represented as textual differences with no regards to the syntactic nature of programming languages or their semantics. Thus, they may be hard to read and often fail to convey insight on the changes on semantics. Furthermore, such low-level, unstructured presentations are hard to reason about.

We present a formal framework to characterize differences between deterministic programs in terms of their small-step semantics. This language-agnostic framework defines the notion of /difference languages/ in which /oracles/—programs that relate small-step executions of pairs of program written in a same language—can be written, reasoned about and composed.

We illustrate this framework by instantiating it on a toy imperative language and by presenting several /difference languages/ ranging from trivial equivalence-preserving syntactic transformations to characterized semantic differences. Through those examples, we will present the basis of our framework, show how to use it to relate syntactic changes with their effect on semantics, how one can abstract away from the small-step semantics presentation, and discuss the composability of oracles.

This is joint work with Thibaut Girka (IRIF - MERCE) and David Mentré (MERCE)

Mercredi 07 décembre 2016 · 11h00 · Salle 1007

Combinatoire énumérative et analytique · Cedric Boutillier (UPMC) · ??

Vendredi 09 décembre 2016 · 14h30 · Salle 1006

Automates · Benjamin Hellouin (IRIF) · TBA