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Counting equilibria of large complex systems by instability index

Research output: Contribution to journalArticlepeer-review

Gérard Ben Arous, Yan V. Fyodorov, Boris A. Khoruzhenko

Original languageEnglish
Article numbere2023719118
JournalProceedings of the National Academy of Sciences of the United States of America
Issue number34
Accepted/In press29 Jun 2021
Published24 Aug 2021

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Publisher Copyright: © 2021 National Academy of Sciences. All rights reserved. Copyright: Copyright 2021 Elsevier B.V., All rights reserved.


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We consider a nonlinear autonomous system of N ≫ 1 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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