The Lifting Bifurcation Problem on Feed-Forward Networks

TL;DR

This paper investigates the bifurcation behavior in feed-forward networks, showing how lifts affect bifurcation branches and identifying conditions under which new solutions emerge independently of smaller systems.

Contribution

It characterizes the structure of lifts in feed-forward networks and analyzes the bifurcation phenomena, revealing when additional bifurcating solutions can occur.

Findings

Lifts in feed-forward networks are composed of layer-creating and intra-layer lifts.

Most lifts lead to additional bifurcating branches due to increased center subspace.

Bifurcations involving internal dynamics depend on specific system details when lifts occur inside layers.

Abstract

We consider feed-forward networks, that is, networks where cells can be divided into layers, such that every edge targeting a layer, excluding the first one, starts in the prior layer. A feed-forward system is a dynamical system that respects the structure of a feed-forward network. The synchrony subspaces for a network, are the subspaces defined by equalities of some cells coordinates, that are flow-invariant by all the network systems. The restriction of each network system to each synchrony subspace is a system associated with a smaller network, which may be, or not, a feed-forward network. The original network is then said to be a lift of the smaller network. We show that a feed-forward lift of a feed-forward network is given by the composition of two types of lifts: lifts that create new layers and lifts inside a layer. Furthermore, we address the lifting bifurcation problem on feed-forward systems. More precisely, the comparison of the possible codimension-one local steady-state bifurcations of a feed-forward system and those of the corresponding lifts is considered. We show that for most of the feed-forward lifts, the increase of the center subspace is a sufficient condition for the existence of additional bifurcating branches of solutions, which are not lifted from the restricted system. However, when the bifurcation condition is associated with the internal dynamics and the lifts occurs inside an intermediate layer, we prove that the existence of bifurcating branches of solutions that are not lifted from the restricted system does depend generically on the particular feed-forward system.