The Finite Groups of Random Walks in the Quarter Plane and Periodic 4-bar Links (Les groupes finis de marches aléatoires dans un quart de plan et les quadrilatères articulés périodiques)
par
Salle du conseil
PARIS
We present our solutions to two long standing open problems, the first one from probability theory, formulated by Malyshev in 1970 and the second one from a crossroad of geometry and dynamics, posed by Darboux in 1879. The Malyshev problem is of finding effective, explicit necessary and sufficient conditions in the closed form to characterize all random walks in the quarter plane with the group of the random walk of order 2n, for all n ≥ 2. The previously known results covered the cases n=2, 3, and 4. We describe all n-periodic Darboux transformations for 4-bar link problems for all n ≥ 2, thus completely solving the Darboux problem, that he solved for n = 2 in 1879. This is based on a joint work with Milena Radnovic (arXiv: 2512:21976).
Sémimaire ASD, Alain Albouy, Alain Chenciner, Jacques Laskar