# Complex-balanced equilibria of generalized mass-action systems: Necessary conditions for linear stability

## TL;DR

This paper investigates the stability of complex-balanced equilibria in generalized mass-action systems, establishing necessary conditions for linear stability and characterizing stability properties for specific network types.

## Contribution

It introduces new criteria linking matrix stability notions to the linear stability of equilibria in generalized mass-action systems, extending classical results.

## Key findings

- Linear stability implies uniqueness of equilibria.
- Characterization of stability for cyclic networks via D-stability.
- Necessary conditions for stability in weakly reversible networks.

## Abstract

It is well known that, for mass-action systems, complex-balanced equilibria are asymptotically stable. For generalized mass-action systems, even if there exists a unique complex-balanced equilibrium (in every stoichiometric class and for all rate constants), it need not be stable. We first discuss several notions of matrix stability (on a linear subspace) such as D-stability and diagonal stability, and then we apply our abstract results to complex-balanced equilibria of generalized mass-action systems. In particular, we show that linear stability (on the stoichiometric subspace and for all rate constants) implies uniqueness. For cyclic networks, we characterize linear stability (in terms of D-stability of the Jacobian matrix); and for weakly reversible networks, we give necessary conditions for linear stability (in terms of D-semistability of the Jacobian matrices of all cycles in the network). Moreover, we show that, for classical mass-action systems, complex-balanced equilibria are not just asymptotically stable, but even diagonally stable (and hence linearly stable). Finally, we recall and extend characterizations of D-stability and diagonal stability for matrices of dimension up to three, and we illustrate our results by examples of irreversible cycles (of dimension up to three) and of reversible chains and S-systems (of arbitrary dimension).