Reduction of Interaction Delays in Networks

TL;DR

This paper introduces a method to simplify delay differential equation models of coupled systems by reducing the number of distinct delays through a componentwise timeshift transformation, preserving dynamics.

Contribution

It identifies invariants and conditions under which multiple delays can be reduced, providing a normal form and linking delay reduction to network topology.

Findings

Networks with equal sums of delays along fundamental cycles are dynamically equivalent.

The method reduces an 8-delay motif to an equivalent 3-delay motif.

The approach preserves the system's dynamics while simplifying the model.

Abstract

Delayed interactions are a common property of coupled natural systems and therefore arise in a variety of different applications. For instance, signals in neural or laser networks propagate at finite speed giving rise to delayed connections. Such systems are often modeled by delay differential equations with discrete delays. In realistic situations, these delays are not identical on different connections. We show that by a componentwise timeshift transformation it is often possible to reduce the number of different delays and simplify the models without loss of information. We identify dynamic invariants of this transformation, determine its capabilities to reduce the number of delays and interpret these findings in terms of the topology of the underlying graph. In particular, we show that networks with identical sums of delay times along the fundamental semicycles are dynamically equivalent and we provide a normal form for these systems. We illustrate the theory using a network motif of coupled Mackey-Glass systems with 8 different time delays, which can be reduced to an equivalent motif with three delays.