Symplectomorphisms and discrete braid invariants

Area and orientation preserving diffeomorphisms of the standard 2-disc, referred to as symplectomorphisms of $\mathbb{D}^{2}$, allow decompositions in terms of positive twist diffeomorphisms. Using the latter decomposition we utilize the Conley index theory of discrete braid classes as introduced in [Ghrist et al., C. R. Acad. Sci. Paris S\'er. I Math., 331(11), 2000, Invent. Math., 152(2), 2003] in order to obtain a Morse type forcing theory of periodic points: a priori information about periodic points determines a mapping class which may force additional periodic points.Comment: 31 pages, in print in Journal of Fixed Point Theory and Application

Existence of periodic solutions of the FitzHugh-Nagumo equations for an explicit range of the small parameter

The FitzHugh-Nagumo model describing propagation of nerve impulses in axon is given by fast-slow reaction-diffusion equations, with dependence on a parameter $\epsilon$ representing the ratio of time scales. It is well known that for all sufficiently small $\epsilon>0$ the system possesses a periodic traveling wave. With aid of computer-assisted rigorous computations, we prove the existence of this periodic orbit in the traveling wave equation for an explicit range $\epsilon \in (0, 0.0015]$. Our approach is based on a novel method of combination of topological techniques of covering relations and isolating segments, for which we provide a self-contained theory. We show that the range of existence is wide enough, so the upper bound can be reached by standard validated continuation procedures. In particular, for the range $\epsilon \in [1.5 \times 10^{-4}, 0.0015]$ we perform a rigorous continuation based on covering relations and not specifically tailored to the fast-slow setting. Moreover, we confirm that for $\epsilon=0.0015$ the classical interval Newton-Moore method applied to a sequence of Poincar\'e maps already succeeds. Techniques described in this paper can be adapted to other fast-slow systems of similar structure

Rigorous numerics for PDEs with indefinite tail: existence of a periodic solution of the Boussinesq equation with time-dependent forcing

We consider the Boussinesq PDE perturbed by a time-dependent forcing. Even though there is no smoothing effect for arbitrary smooth initial data, we are able to apply the method of self-consistent bounds to deduce the existence of smooth classical periodic solutions in the vicinity of 0. The proof is non-perturbative and relies on construction of periodic isolating segments in the Galerkin projections

Periodic orbits of the FitzHugh-Nagumo equations - a computer assisted proof

Non UBCUnreviewedAuthor affiliation: Jagiellonian UniversityGraduat

Metody indeksu Conleya na przestrzeniach warkoczy w niskowymiarowych układach dynamicznych

Proponujemy metodę zdefiniowania indeksu Conleya dla przestrzeni warkoczy dopuszczających negatywne przecięcia. Poprzez rozkład dyfeomorfizmów (względnie symplektomorfizmów) płaszczyzny o zwartym nośniku na dyfeomorfizmy (symplektomorfizmy) z własnością pozytywnego twistu sprowadzamy sytuację do przypadku wyłącznie z pozytywnymi przecięciami. Omawiamy metody obliczania indeksu oraz możliwe zastosowania.The purpose of this thesis is to propose a framework for developing a forcingtheory on spaces of arbitrary braids. We establish a method of decomposingcompactly supported diffeomorphisms of the plane to positive twist mappingsand relate them to the recently developed machinery of Conley indexfor positive braid diagrams. Area preserving case is also covered. We discusspossible dynamical implications in study of non-Lagrangian systemsvia Poincaré maps

Safe Multi-agent Learning via Trapping Regions

One of the main challenges of multi-agent learning lies in establishing convergence of the algorithms, as, in general, a collection of individual, self-serving agents is not guaranteed to converge with their joint policy, when learning concurrently. This is in stark contrast to most single-agent environments, and sets a prohibitive barrier for deployment in practical applications, as it induces uncertainty in long term behavior of the system. In this work, we apply the concept of trapping regions, known from qualitative theory of dynamical systems, to create safety sets in the joint strategy space for decentralized learning. We propose a binary partitioning algorithm for verification that candidate sets form trapping regions in systems with known learning dynamics, and a heuristic sampling algorithm for scenarios where learning dynamics are not known. We demonstrate the applications to a regularized version of Dirac Generative Adversarial Network, a four-intersection traffic control scenario run in a state of the art open-source microscopic traffic simulator SUMO, and a mathematical model of economic competition