| 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" |
