Counting equilibria of large complex systems by instability index.

Proc Natl Acad Sci U S A

School of Mathematical Sciences, Queen Mary University of London, London E1 4NS, United Kingdom

Published: August 2021

We consider a nonlinear autonomous system of [Formula: see text] degrees of freedom randomly coupled by both relaxational ("gradient") and nonrelaxational ("solenoidal") random interactions. We show that with increased interaction strength, such systems generically undergo an abrupt transition from a trivial phase portrait with a single stable equilibrium into a topologically nontrivial regime of "absolute instability" where equilibria are on average exponentially abundant, but typically, all of them are unstable, unless the dynamics is purely gradient. When interactions increase even further, the stable equilibria eventually become on average exponentially abundant unless the interaction is purely solenoidal. We further calculate the mean proportion of equilibria that have a fixed fraction of unstable directions.

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http://www.ncbi.nlm.nih.gov/pmc/articles/PMC8403947PMC
http://dx.doi.org/10.1073/pnas.2023719118DOI Listing

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