| Links' Seminars and Public Events |   |
| 2024 | |
|---|---|
Fri 15th Nov 11:00 am 12:15 pm | Seminar by Gabriel Bathie Speaker: Gabriel Bathie (perso.ens-lyon.fr/gabriel.bathie/) Room: B21 Title: The complexity of Testing Regular Languages - Gabriel Bathie, Corto Mascle and Nathanaël Fijalkow (LaBRI, Université de Bordeaux) Abstract: Property testing is concerned with the design of algorithms making sublinear number of queries to distinguish whether the input satisfies a given property or is far from having this property. A seminal paper of Alon, Krivelevich, Newman, and Szegedy in 2001 introduced property testing of formal languages: the goal is to determine whether an input word belongs to a given language, or is far from any word in that language (in terms of Hamming distance). They constructed the first property testing algorithm for the class of all regular languages. Somewhat surprisingly, their algorithm uses a number of queries that does not depend on the length of the input word. This opened up a line of work with improved complexity results and applications to streaming algorithms. In this work, we show a trichotomy result: the class of regular languages can be divided into three classes, each of which is associated with an optimal testing complexity. Our analysis yields effective characterizations for all three classes using so-called minimal blocking sequences, reasoning directly and combinatorially on automata. This talk will give an overview of the methods used since the work of Alon et al. and highlight the main tools used for our combinatorial characterization. Based on joint work with Corto Mascle and Nathanaël Fijalkow. "Lille-Salle B21" |
Tue 12th Nov 2:00 pm 3:30 pm | Seminar from Aliaume Lopez Speaker: Aliaume Lopez (www.lsv.fr/~lopez/) Title: Which polynomials are computed by N-weighted automata? Room: B21 Abstract: Given a semiring K, the notion of K-weighted automata generalizes regular languages to functions from Σ* to K. This model allows us to compute (multivariate) polynomial functions with coefficients in K. We provide a decidable characterization of polynomials with coefficients in Q that can be computed by K-weighted automata for K = (N,+,×) and for K = (Z+,×). As a consequence, we can decide which functions computed by Z-weighted automata are computed by N-weighted automata, under the assumption of commutativity (the order of the letters in the input does not matter) and polynomial growth (the output of the function is bounded by a polynomial in the size of the input). This surprisingly allows us to decide whether such functions are star-free, a notion borrowed from the theory of regular languages. "Lille-Salle B21" |
Fri 11th Oct 10:30 am 12:00 pm | Seminar from Alexis de Colnet Speaker: Alexis de Colnet (www.ac.tuwien.ac.at/people/decolnet/) Title: An FPRAS for #NFA and #nFBDD Abstract: #NFA is the problem of counting the words of a given length accepted by a non-deterministic finite automaton (NFA). The problem is #P-hard but the approximate variant admits polynomial-time randomized algorithms (FPRAS, or fully-polynomial time randomized approximation schemes). Arenas, Croquevielle, Jayaram and Riveros were the first to show that #NFA admits an FPRAS and that this result extends to several other counting problems, in fact all problems in the class SpanL. In this talk we present another FPRAS for #NFA which applies to problems not covered by Arenas et al.'s result. In particular, the FPRAS described in this talk can be used for the problem of counting the satisfying assignments of non-deterministic read-once branching programs (nFBDD).  Atrium bâtiment Esprit |
Fri 7th Jun 10:00 am 11:00 am | Séminaire Sam Van Gool dualité de Stone |
Thu 30th May to Fri 31st May all day | Pysemigroup Hackaton |
Fri 24th May 11:00 am 11:30 am | Séminaire Sophie Tison Speaker: Sophie Tison Title: Containment of Regular Path Queries Under Constraints |
Thu 16th May 2:00 pm 4:00 pm | Seminar Arkaprava Title: Efficient Optimization of Network Metrics in Large Uncertain Graphs Abstract: Graphs constitute an omnipresent data structure that can model objects and their relationships in a wide variety of real-world scenarios. The optimization of network metrics finds use in a plethora of real-world applications. Most of the exact techniques for such tasks turn out to be prohibitively time-consuming and memory-intensive for the huge graphs that are usually encountered. Thus, there is a need for efficient approximation algorithms. This talk focuses on the efficient optimization of network metrics in large uncertain graphs, and specifically the following three research problems. The first problem aims to find, between a given pair of nodes in an uncertain graph, the path having the highest probability of being a shortest path. The second problem aims to find, in an uncertain graph, the subgraph having the highest probability of being densest. The third problem is a novel variant of the well-known opinion maximization problem where, given a social network of users with real-valued opinions (about different candidates), the goal is to choose the top-k seed users maximizing a specific voting-based score at a given finite time horizon. Best Regards, Arkaprava "Lieu : Lille, Salle : B11" |
Fri 19th Apr 11:00 am 12:00 pm | Seminar Pierre Lermusiaux Speaker: Pierre Lermusiaux (plermusi.github.io/) Title: Detection of Uncaught Exceptions in Functional Programs by Abstract Interpretation Abstract: Exception handling is a key feature in modern programming languages. Exceptions can be used to deal with errors, or as a means to control the flow of execution of a program. Since they might unexpectedly terminate a program, unhandled exceptions are a serious safety concern. We propose a static analysis to detect uncaught exceptions in functional programs, that is defined as an abstract interpreter. It computes a description of the values potentially returned by a program using a novel abstract domain, that can express inductively defined sets of values. Simultaneously, the analysis infers the possibly raised exceptions, by computing in the abstract exception monad. This abstract interpreter has been implemented as an effective static analyser for a large subset of OCaml programs, that supports mutable data types, the OCaml module system, and dynamically extensible data types such as the exception type. The analyser has been evaluated on several hundreds of OCaml programs. |
Fri 5th Apr 10:30 am 11:30 am | Séminaire Guillaume Lagarde Titre: Scaling Neural Program Synthesis with Distribution-based Search Abstract: In this talk, we will discuss the problem of automatically constructing computer programs from input-output examples, especially when the target language is domain-specific and defined using a context-free grammar. I will introduce a theoretical framework called distribution-based search, discuss its challenges, and present several search strategies based on learning the weights of a probabilistic context-free grammar (PCFG) and then using this PCFG to enumerate the most promising candidate programs efficiently. The presentation will be based on the following paper published at AAAI'2022: arxiv.org/abs/2110.12485 Joint work with Nathanaël Fijalkow, Théo Matricon, Kevin Ellis, Pierre Ohlmann, Akarsh Potta |
Fri 2nd Feb 10:30 am 11:30 am | Mikaël Monet: Probabiliste Shapley value |
Fri 26th Jan 10:00 am 11:00 am | Séminaire: Klara Nosan Sujet: TBA |
| 2023 | |
Thu 14th Dec 2:00 pm 5:00 pm | Claire Soyez-Martin PhD defense Amphi IRCICA |
Fri 1st Dec 10:00 am 11:00 am | Séminaire Oliver Titre: Direct Access for Conjunctive Queries with Negation Abstract: Direct Access is the operation of returning, given an index j, the jth answer of a conjunctive query on a given database for a given order. While this problem is #P-hard in general (wrt combined complexity), many conjunctive queries are structured enough so that for some lexicographical ordering of their answers, one can have a direct access to the answer set of a query Q that takes polylogarithmic time in the size of the database after a polynomial time precomputation. Previous work has precisely characterised the tractable classes and given fined-grained lower bounds on the time needed for precomputation depending on the structure of the query. We give a generalisation of these tractability results to the case of signed conjunctive queries, that is, conjunctive queries that may contain negative atoms. Our technique is based on solving the direct access task for a class of circuits that can represent relational data. Our result then follows from the fact that the tractable (signed) conjunctive queries can be transformed into polynomial size circuits. We recover the known tractable classes from the literature in the case of positive conjunctive queries using this technique and also discover new islands of tractability for signed conjunctive queries. In particular, our result generalises to the Direct Access Problem the known tractabilities of counting the number of answers to beta-acyclic negative queries and of deciding whether a negative query with bounded nested-width has an answer. This is joint work with Florent Capelli. |
Fri 24th Nov 10:00 am 11:00 am | Séminaire Pierre Vandenhove |
Fri 17th Nov 10:00 am 11:00 am | Séminaire Charles (RsonPath) TBA |
Fri 10th Nov 10:00 am 11:00 am | Séminaire Nils Vortmeier title: TBA |
Fri 20th Oct 10:30 am 12:30 pm | Aurelien part II |
Fri 22nd Sep 11:00 am 12:00 pm | Séminaire Théo Losekoot Title: Automata-based verification of relational properties of functions over algebraic data structures |
Fri 15th Sep 11:00 am 12:30 pm | Charles: Présentation de rsonpath |
