| Links' Seminars and Public Events |   |
| 2024 | |
|---|---|
Fri 15th Nov 11:00 am 12:15 pm | Seminar by Gabriel Bathie "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 |
