Links' Seminars and Public Events | ![]() ![]() |
2024 | |
---|---|
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 |
Fri 23rd Jun 11:00 am 12:00 pm | Seminar by Florent Capelli Speaker: Florent Capelli — florent.capelli.me/ Title: A simpler FPRAS for nOBDD Abstract: A simpler FPRAS for nOBDD Abstract: In this talk, we revisit the algorithm by Arenas, Croquevielle, Jayaram and Riveros that allows to approximate the number of words of length n of a non deterministic finite automaton. We explain the algorithm and techniques in a modular and general way, without relating to the particular case of counting words in automaton. We illustrate the soundness of the approach by applying it to the problem of approximatively counting the number of satisfying assignments of a non-deterministic OBDD. B21 |
Fri 2nd Jun 11:00 am 12:30 pm | Séminaire Martin Berger Title: Search-Based Regular Expression Inference on a GPU Abstract: Regular expression inference (REI) is a supervised machine learning and program synthesis problem that takes a cost metric for regular expressions, and positive and negative examples of strings as input. It outputs a regular expression that is precise (i.e., accepts all positive and rejects all negative examples), and minimal w.r.t. to the cost metric. We present a novel algorithm for REI over arbitrary alphabets that is enumerative and trades off time for space. Our main algorithmic idea is to implement the search space of regular expressions succinctly as a contiguous matrix of bitvectors. Collectively, the bitvectors represent, as characteristic sequences, all sub-languages of the infix-closure of the union of positive and negative examples. Mathematically, this is a semiring of (a variant of) formal power series. Infix-closure enables bottom-up compositional construction of larger from smaller regular expressions using the operations of our semiring. This minimises data movement and data-dependent branching, hence maximises data-parallelism. In addition, the infix-closure remains unchanged during the search, hence search can be staged: first pre-compute various expensive operations, and then run the compute intensive search process. We provide two C++ implementations, one for general purpose CPUs and one for Nvidia GPUs (using CUDA). We benchmark both on Google Colab Pro: the GPU implementation is on average over 1000x faster than the CPU implementation on the hardest benchmarks. Joint work with Mojtaba Valizadeh Download: martinfriedrichberger.net/pldi2023.html |