Mardi 12 Décembre
Heure: 
14:00  17:00 
Lieu: 
Salle B107, bâtiment B, Université de Villetaneuse 
Résumé: 
Analysis of the Brun GCD Algorithm. TBA 
Description: 
Loïck Lhote 
Heure: 
15:00  18:00 
Lieu: 
Salle B107, bâtiment B, Université de Villetaneuse 
Résumé: 
A graphbased method to randomly generate subgroups of free groups 
Description: 
Pascal Weil The study of random algebraic objects sheds a different light on these objects, which complements the algebraic and the algorithmic points of view. When it comes to finitely generated subgroups of free groups, we have a remarkable graphical representation calledthe Stallings graph: the Stallings graph of a subgroup H is a finite labeled graph uniquely associated with H, efficiently computed from a set of generators of H (say, given as reduced words), and from which one can efficiently compute many invariants of H.I will discuss enumerating and randomly generating finitely generated subgroups of free groups, for the distribution given by Stallings graphs: for each positive integer n, one considers the finite number of subgroups whose Stallings graph has n vertices, and oneconsiders the uniform distribution on that set. This requires understanding the combinatorial structure of Stallings graphs, which are interesting objects per se. I will also exhibit natural properties of subgroups which are `generic' for this distribution.This is joint work with F. Bassino (LIPN) and C. Nicaud (LIGM) 

