### Forward attractors and limit sets of nonautonomous difference equations

- Series
- CDSNS Colloquium
- Time
- Friday, February 5, 2021 - 13:00 for 1 hour (actually 50 minutes)
- Location
- Zoom (see add'l notes for link)
- Speaker
- Peter Kloeden – Universität Tübingen – kloeden@math.uni-frankfurt.de

**Please Note:** Zoom link: https://zoom.us/j/97732215148?pwd=Z0FBNXNFSy9mRUx3UVk4alE4MlRHdz09

The theory of nonautonomous dynamical systems has undergone major development during the past 23 years since I talked about attractors of nonautonomous difference equations at ICDEA Poznan in 1998.

Two types of attractors consisting of invariant families of sets have been defined for nonautonomous difference equations, one using pullback convergence with information about the system in the past and the other using forward convergence with information about the system in the future. In both cases, the component sets are constructed using a pullback argument within a positively invariant family of sets. The forward attractor so constructed also uses information about the past, which is very restrictive and not essential for determining future behaviour.

The forward asymptotic behaviour can also be described through the omega-limit set of the system.This set is closely related to what Vishik called the uniform attractor although it need not be invariant. It is shown to be asymptotically positively invariant and also, provided a future uniformity condition holds, also asymptotically positively invariant. Hence this omega-limit set provides useful information about the behaviour in current time during the approach to the future limit.