A Perron-Frobenius strong threshold theorem for (A, B, P, {φ}) balanced bilinear models, and the role of left and right Perron eigenvectors in mathematical epidemiology
Pith reviewed 2026-06-30 11:57 UTC · model grok-4.3
The pith
A nontrivial positive endemic equilibrium exists in these bilinear models precisely when the spectral equation ρ(K̃(S))=1 admits a strictly positive solution.
A machine-rendered reading of the paper's core claim, the machinery that carries it, and where it could break.
Core claim
In (A, B, P, ϕ) balanced bilinear models whose next-generation matrix K = F(S)V^{-1} satisfies the structural conditions for the Perron-Frobenius theorem, a nontrivial positive equilibrium exists if and only if ρ(K̃(S))=1 admits a strictly positive solution S; the left Perron eigenvector π(S) yields Lyapunov functions establishing the global stability exchange between the disease-free and endemic equilibria, while the right eigenvector w(S) governs the exit direction from the siphon face.
What carries the argument
The next-generation matrix K = F(S)V^{-1} together with its left and right Perron eigenvectors π(S) and w(S) for the balanced bilinear structure (A, B, P, ϕ).
If this is right
- Bonzi-Iggidr-Sallet rank-one models split into two explicit classes whose equilibria and eigenvectors are given by closed formulas.
- Lyapunov functions for both equilibria are obtained directly from the left Perron eigenvector of the next-generation matrix.
- The threshold result extends beyond rank one by replacing explicit eigenvector formulas with the spectral equation ρ(K̃(S))=1.
- Feedback from infectious to susceptible compartments preserves the eigenvector-based Lyapunov construction.
Where Pith is reading between the lines
- The same left-eigenvector weighting may produce global stability certificates in non-rank-one next-generation matrices once the spectral condition is verified.
- Numerical continuation of the equation ρ(K̃(S))=1 could locate the endemic equilibrium without solving the full algebraic system.
- The exit direction given by the right eigenvector suggests a practical test for whether an observed outbreak trajectory is leaving the disease-free state along the predicted ray.
Load-bearing premise
The system must belong to the (A, B, P, ϕ) balanced bilinear family so that the next-generation matrix obeys the positivity and irreducibility conditions needed for a unique positive Perron eigenvector.
What would settle it
A concrete (A, B, P, ϕ) model in which ρ(K̃(S)) never equals 1 for any positive S yet a positive endemic equilibrium still exists, or in which ρ(K̃(S))=1 has a positive solution but no positive equilibrium appears.
read the original abstract
This paper started as a review of seven results pertaining to a family of bilinear models with rank one NGM introduced by Fall, Iggidr, Sallet and Bonzi, which utilize the explicit eigenvectors of the NGM to compute the unique endemic equilibrium (EE), and Lyapunov functions at both the disease free equilibrium (DFE) and EE, and of results of Shuai and Van den Driessche (2013), which essentially deal with the same "DFE -EE stability exchange" in the non-rank one case, when the eigenvectors are not explicit. Recently, these results were complemented by Earn and McCluskey (2025), who proved as well a ``strong threshold theorem", namely that when the DFE is unstable, a second equilibrium which is globally asymptotically stable must exist. Below, we obtain in Theorem \ref{thm:TK_DFE} some results that extend beyond rank one. For example, a nontrivial positive equilibrium exists if and only if the spectral equation \(\rho(\widetilde K(S))=1\), admits a strictly positive solution. Also, we showed that Bonzi-Iggidr-Sallet bilinear models with rank one NGM may be classified in two classes, with slight variations in the eigenvector formulas, and that extensions in the presence of feedback from infectious to susceptible are possible. Another takeout from the previous works, which we clarify in a revisit of the seven results in the rank one case, is that Lyapunov functions for both the DFE and the EE may be constructed using as weights the left Perron eigenvector $\pi(S)$ of the \NGM\ (NGM) $K=F(S) V^{-1}$, where $S$ denote all the non-infectious variables, and when a positive ODE leaves a siphon face, it does so along the right Perron eigenvector $w(S)$ of $\T K= V^{-1}F(S)$. The question of whether this continues to be true beyond rank one is explored in ongoing work.
Editorial analysis
A structured set of objections, weighed in public.
Referee Report
Summary. The manuscript claims a strong threshold theorem for (A, B, P, ϕ) balanced bilinear models: a nontrivial positive equilibrium exists if and only if the spectral equation ρ(K̃(S))=1 admits a strictly positive solution (Theorem TK_DFE). It classifies rank-one NGM models of Bonzi-Iggidr-Sallet into two classes with explicit left/right Perron eigenvector formulas for equilibria and Lyapunov functions, extends prior results on DFE-EE stability exchange, and notes that Lyapunov weights can be taken from the left Perron eigenvector π(S) of K=F(S)V^{-1} while leaving siphons occurs along the right eigenvector w(S).
Significance. If the derivation is complete, the result supplies an explicit if-and-only-if criterion and eigenvector-based constructions that extend rank-one NGM analyses to a broader bilinear family, clarifying the role of Perron vectors in both equilibrium computation and global stability proofs without fitted parameters.
major comments (1)
- [Theorem TK_DFE] Theorem TK_DFE (main result section): the iff claim that a strictly positive equilibrium exists precisely when ρ(K̃(S))=1 has a strictly positive solution presupposes that K̃(S) is irreducible for every admissible S>0 so that Perron-Frobenius supplies a strictly positive eigenvector. No structural hypothesis on the parameters A, B, P, ϕ is stated that guarantees this irreducibility (or primitivity) uniformly in S; without it the eigenvector may be merely nonnegative, breaking both the strict-positivity construction and the Lyapunov arguments that invoke π(S).
Simulated Author's Rebuttal
We thank the referee for the careful reading of the manuscript and for identifying the need for an explicit irreducibility hypothesis in the statement of Theorem TK_DFE. We address the major comment below.
read point-by-point responses
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Referee: [Theorem TK_DFE] Theorem TK_DFE (main result section): the iff claim that a strictly positive equilibrium exists precisely when ρ(K̃(S))=1 has a strictly positive solution presupposes that K̃(S) is irreducible for every admissible S>0 so that Perron-Frobenius supplies a strictly positive eigenvector. No structural hypothesis on the parameters A, B, P, ϕ is stated that guarantees this irreducibility (or primitivity) uniformly in S; without it the eigenvector may be merely nonnegative, breaking both the strict-positivity construction and the Lyapunov arguments that invoke π(S).
Authors: We agree that the current statement of Theorem TK_DFE presupposes irreducibility of K̃(S) for S>0 to invoke the strict positivity of the Perron eigenvector, yet no such structural hypothesis on A, B, P, ϕ is explicitly stated. While the balanced bilinear structure of the models considered often yields irreducible next-generation matrices under standard epidemiological connectivity assumptions, this is not formalized in the manuscript. We will therefore revise the paper to add the explicit assumption that K̃(S) is irreducible (or primitive) for every admissible S>0. This assumption will be incorporated into the hypotheses of Theorem TK_DFE and the subsequent Lyapunov constructions, thereby ensuring the strict-positivity claims hold rigorously. revision: yes
Circularity Check
No significant circularity; central claims rest on standard Perron-Frobenius application to model-derived NGM under stated structural assumptions.
full rationale
The derivation in Theorem TK_DFE equates existence of a strictly positive equilibrium to the spectral equation ρ(K̃(S))=1 admitting a positive solution, constructed via left/right Perron eigenvectors of K=F(S)V^{-1}. This follows directly from the Perron-Frobenius theorem (an external mathematical result) applied to matrices defined from the (A,B,P,ϕ) balanced bilinear family, without any reduction to self-definition, fitted inputs renamed as predictions, or load-bearing self-citations whose content is unverified. The paper reviews prior results on rank-one cases and extends them, but the extension itself supplies independent structural content rather than importing uniqueness via overlapping-author citations. The noted irreducibility requirement is a potential assumption gap (correctness concern) but does not make the stated equivalence tautological or self-referential by construction.
Axiom & Free-Parameter Ledger
axioms (2)
- standard math Perron-Frobenius theorem guarantees a unique positive eigenvector and spectral radius for irreducible nonnegative matrices
- domain assumption The (A, B, P, ϕ) bilinear models satisfy the balanced structural conditions that keep the next-generation matrix nonnegative and allow the spectral equation to be well-posed
Reference graph
Works this paper leans on
-
[1]
Global asymptotic stability for a class of nonlinear chemical equations.SIAM Journal on Applied Mathematics, 68(5):1464–1476, 2008
David F Anderson. Global asymptotic stability for a class of nonlinear chemical equations.SIAM Journal on Applied Mathematics, 68(5):1464–1476, 2008. 1
2008
-
[2]
Finite time distributions of stochas- tically modeled chemical systems with absolute concentration robustness.SIAM Journal on Applied Dynamical Systems, 16(3):1309–1339, 2017
David F Anderson, Daniele Cappelletti, and Thomas G Kurtz. Finite time distributions of stochas- tically modeled chemical systems with absolute concentration robustness.SIAM Journal on Applied Dynamical Systems, 16(3):1309–1339, 2017. 1.3
2017
-
[3]
A petri net approach to the study of persistence in chemical reaction networks.Mathematical biosciences, 210(2):598–618, 2007
David Angeli, Patrick De Leenheer, and Eduardo D Sontag. A petri net approach to the study of persistence in chemical reaction networks.Mathematical biosciences, 210(2):598–618, 2007. 2, 2, 1, 2, 3
2007
-
[4]
Some probabilistic interpretations related to the next-generation matrix theory: A review with examples.Mathematics, 12(15):2425, 2024
Florin Avram, Rim Adenane, and Lasko Basnarkov. Some probabilistic interpretations related to the next-generation matrix theory: A review with examples.Mathematics, 12(15):2425, 2024. 2 33
2024
-
[5]
Florin Avram, Rim Adenane, Lasko Basnarkov, Gianluca Bianchin, Dan Goreac, and Andrei Halanay. An age of infection kernel, anRformula, and further results for Arino–Brauer A, B matrix epidemic models with varying populations, waning immunity, and disease and vaccination fatalities.Mathemat- ics, 11(6):1307, 2023. 1.5
2023
-
[6]
On SIR-PH epi- demic models and their associated semi-groups and renewal kernels.Monografias Matematicas Garcia de Galdeano, 2022
Florin Avram, Rim Adenane, Lasko Basnarkov, Dan Goreac, and Andrei Halanay. On SIR-PH epi- demic models and their associated semi-groups and renewal kernels.Monografias Matematicas Garcia de Galdeano, 2022. 1
2022
-
[7]
Florin Avram, Rim Adenane, Lasko Basnarkov, and Andras Horvath. The similarity between epi- demiologic strains, minimal self-replicable siphons, and autocatalytic cores in (chemical) reaction networks: Towards a unifying framework.Mathematics, 14(1):23, 2025. 1.3
2025
-
[8]
Algorithmic approach for a unique definition of the next-generation matrix.Mathematics, 12(1):27, 2023
Florin Avram, Rim Adenane, Lasko Basnarkov, and Matthew D Johnston. Algorithmic approach for a unique definition of the next-generation matrix.Mathematics, 12(1):27, 2023. 2
2023
-
[9]
New results and open questions for sir-ph epidemic models with linear birth rate, loss of immunity, vaccination, and disease and vaccination fatalities
Florin Avram, Rim Adenane, and Andrei Halanay. New results and open questions for sir-ph epidemic models with linear birth rate, loss of immunity, vaccination, and disease and vaccination fatalities. Symmetry, 14(5):995, 2022. 1, 1.5, 3.4
2022
-
[10]
Relay transitions and invasion thresholds in multi-strain rumor models: a chemical reaction network approach.preprint, 2026
Florin Avram, Rim Adenane, and Andrei D Halanay. Relay transitions and invasion thresholds in multi-strain rumor models: a chemical reaction network approach.preprint, 2026. 1, 2, 3, 2
2026
-
[11]
Halanay, and Matthew D
Florin Avram, Rim Adenane, Andrei D. Halanay, and Matthew D. Johnston. Investigating synergies between chemical reaction networks (CRN) and mathematical epidemiology (ME), using the Mathe- matica package Epid-CRN, 2024. 3
2024
-
[12]
Florin Avram, Rim Adenane, and Andrei-Dan Halanay. A cocktail of chemical reaction networks and mathematical epidemiology tools for positive ode stability problems: a generalized next generation matrix theorem, an epid-crn implementation of the child-selection ex- pansion, and a semi-parametric analysis of a capasso-type sir epidemic model with functional...
2026
-
[13]
Advancing mathematical epidemiology and chemical reaction network theory via synergies between them.Entropy, 26(11):936, 2024
Florin Avram, Rim Adenane, and Mircea Neagu. Advancing mathematical epidemiology and chemical reaction network theory via synergies between them.Entropy, 26(11):936, 2024. 3, 2
2024
-
[14]
Stability of differential suscepti- bility and infectivity epidemic models.Journal of mathematical biology, 62(1):39–64, 2011
Bernard Bonzi, AA Fall, Abderrahman Iggidr, and Gauthier Sallet. Stability of differential suscepti- bility and infectivity epidemic models.Journal of mathematical biology, 62(1):39–64, 2011. 1, 1.5, 2, 2.3, 1, 4, 3.3
2011
-
[15]
Lorena C Bulhosa and Juliane F Oliveira. Vaccination in a two-strain model with cross-immunity and antibody-dependent enhancement.arXiv preprint arXiv:2302.02263, 2023. 1
-
[16]
Polynomial dynamical systems, reaction networks, and toric differential inclu- sions.SIAM Journal on Applied Algebra and Geometry, 3(1):87–106, 2019
Gheorghe Craciun. Polynomial dynamical systems, reaction networks, and toric differential inclu- sions.SIAM Journal on Applied Algebra and Geometry, 3(1):87–106, 2019. 1.1
2019
-
[17]
Endotactic networks and toric differential inclusions
Gheorghe Craciun and Abhishek Deshpande. Endotactic networks and toric differential inclusions. SIAM Journal on Applied Dynamical Systems, 19(3):1798–1822, 2020. 1.1
2020
-
[18]
Persistence and permanence of mass-action and power-law dynamical systems.SIAM Journal on Applied Mathematics, 73(1):305–329, 2013
Gheorghe Craciun, Fedor Nazarov, and Casian Pantea. Persistence and permanence of mass-action and power-law dynamical systems.SIAM Journal on Applied Mathematics, 73(1):305–329, 2013. 1.1 34
2013
-
[19]
On the definition and the compu- tation of the basic reproduction ratio r0 in models for infectious diseases in heterogeneous populations
Odo Diekmann, Johan Andre Peter Heesterbeek, and Johan AJ Metz. On the definition and the compu- tation of the basic reproduction ratio r0 in models for infectious diseases in heterogeneous populations. Journal of mathematical biology, 28(4):365–382, 1990. 1.5, 5
1990
-
[20]
Global stability of epidemic models with uniform suscep- tibility.Proceedings of the National Academy of Sciences, 122(49):e2510156122, 2025
David JD Earn and C Connell McCluskey. Global stability of epidemic models with uniform suscep- tibility.Proceedings of the National Academy of Sciences, 122(49):e2510156122, 2025. 1, 3.3
2025
-
[21]
Epidemiological models and lya- punov functions.Mathematical Modelling of Natural Phenomena, 2(1):62–83, 2007
A Fall, Abderrahman Iggidr, Gauthier Sallet, and Jean-Jules Tewa. Epidemiological models and lya- punov functions.Mathematical Modelling of Natural Phenomena, 2(1):62–83, 2007. 1, 1.5, 2, 1, 2, 4, 4, 3.3
2007
-
[22]
Elisenda Feliu and Anne Shiu. From chemical reaction networks to algebraic and polyhedral geometry–and back again.arXiv preprint arXiv:2501.06354, 2025. 1
-
[23]
A geometric approach to the global attractor conjecture.SIAM Journal on Applied Dynamical Systems, 13(2):758–797, 2014
Manoj Gopalkrishnan, Ezra Miller, and Anne Shiu. A geometric approach to the global attractor conjecture.SIAM Journal on Applied Dynamical Systems, 13(2):758–797, 2014. 1.1
2014
-
[24]
Guerra, Shelly Bolotin, Gillian Lim, Jane Heffernan, and Shelley L
Fiona M. Guerra, Shelly Bolotin, Gillian Lim, Jane Heffernan, and Shelley L. Deeks. The basic re- production numberr 0 of measles: a systematic review.The Lancet Infectious Diseases, 17(12):e420– e428, 2017. 3
2017
-
[25]
Li, and Zhisheng Shuai
Hongbin Guo, Michael Y . Li, and Zhisheng Shuai. Global stability of the endemic equilibrium of multigroup SIR epidemic models.Canadian Applied Mathematics Quarterly, 14(3):259–284, 2006. 5
2006
-
[26]
On the inverse problem of reaction kinetics.Qualitative theory of differen- tial equations, 30:363–379, 1981
Vera H ´ars and J´anos T´oth. On the inverse problem of reaction kinetics.Qualitative theory of differen- tial equations, 30:363–379, 1981. 1
1981
-
[27]
Generalizations of the ‘linear chain trick’: incorporating more flexible dwell time distributions into mean field ode models.Journal of mathematical biology, 79(5):1831–1883, 2019
Paul J Hurtado and Adam S Kirosingh. Generalizations of the ‘linear chain trick’: incorporating more flexible dwell time distributions into mean field ode models.Journal of mathematical biology, 79(5):1831–1883, 2019. 2
2019
-
[28]
Global analysis of new malaria intrahost models with a competitive exclusion principle.SIAM Journal on Applied Mathematics, 67(1):260–278, 2006
Abderrhaman Iggidr, Jean-Claude Kamgang, Gauthier Sallet, and Jean-Jules Tewa. Global analysis of new malaria intrahost models with a competitive exclusion principle.SIAM Journal on Applied Mathematics, 67(1):260–278, 2006. 1, 1.5, 2, 2.3, 3.3
2006
-
[29]
Weak dynamical nonemptiability and persistence of chemical kinetics systems.SIAM Journal on Applied Mathematics, 71(4):1263–1279, 2011
Matthew D Johnston and David Siegel. Weak dynamical nonemptiability and persistence of chemical kinetics systems.SIAM Journal on Applied Mathematics, 71(4):1263–1279, 2011. 1
2011
-
[30]
On the generalized” birth-and-death” process.The annals of mathematical statistics, 19(1):1–15, 1948
David G Kendall. On the generalized” birth-and-death” process.The annals of mathematical statistics, 19(1):1–15, 1948. 5
1948
-
[31]
Stability of epidemic models over directed graphs: A positive systems approach.Automatica, 74:126–134, 2016
Ali Khanafer, Tamer Bas ¸ar, and Bahman Gharesifard. Stability of epidemic models over directed graphs: A positive systems approach.Automatica, 74:126–134, 2016. 1.5
2016
-
[32]
Global stability for the seir model in epidemiology.Mathe- matical biosciences, 125(2):155–164, 1995
Michael Y Li and James S Muldowney. Global stability for the seir model in epidemiology.Mathe- matical biosciences, 125(2):155–164, 1995. 1.1
1995
-
[33]
A geometric approach to global-stability problems.SIAM Journal on Mathematical Analysis, 27(4):1070–1083, 1996
Michael Y Li and James S Muldowney. A geometric approach to global-stability problems.SIAM Journal on Mathematical Analysis, 27(4):1070–1083, 1996. 1.1
1996
-
[34]
Dynamics of differential equations on invariant manifolds
Michael Y Li and James S Muldowney. Dynamics of differential equations on invariant manifolds. Journal of Differential Equations, 168(2):295–320, 2000. 1.1 35
2000
-
[35]
Catalyst: Fast and flexible modeling of reaction networks.PLOS Computational Biology, 19(10):e1011530, 2023
Torkel E Loman, Yingbo Ma, Vasily Ilin, Shashi Gowda, Niklas Korsbo, Nikhil Yewale, Chris Rack- auckas, and Samuel A Isaacson. Catalyst: Fast and flexible modeling of reaction networks.PLOS Computational Biology, 19(10):e1011530, 2023. 2
2023
-
[36]
Norris.Markov Chains
J.R. Norris.Markov Chains. Cambridge Series in Statistical and Probabilistic Mathematics. Cam- bridge University Press, 1997. 5
1997
-
[37]
Global dynamics of a two-strain disease model with latency and saturating incidence rate.Canadian Applied Mathematics Quarterly, 20(1):51–73, 2012
SM ASHRAFUR Rahman and XINGFU Zou. Global dynamics of a two-strain disease model with latency and saturating incidence rate.Canadian Applied Mathematics Quarterly, 20(1):51–73, 2012. 1
2012
-
[38]
Scalable control of positive systems.European Journal of Control, 24:72–80, 2015
Anders Rantzer. Scalable control of positive systems.European Journal of Control, 24:72–80, 2015. 1.1
2015
-
[39]
Structural sources of robustness in biochemical reaction networks
Guy Shinar and Martin Feinberg. Structural sources of robustness in biochemical reaction networks. Science, 327(5971):1389–1391, 2010. 1.3
2010
-
[40]
Global dynamics of cholera models with differential infec- tivity.Mathematical biosciences, 234(2):118–126, 2011
Zhisheng Shuai and P Van den Driessche. Global dynamics of cholera models with differential infec- tivity.Mathematical biosciences, 234(2):118–126, 2011. 1.5
2011
-
[41]
Global stability of infectious disease models using Lyapunov functions.SIAM Journal on Applied Mathematics, 73(4):1513–1532, 2013
Zhisheng Shuai and Pauline van den Driessche. Global stability of infectious disease models using Lyapunov functions.SIAM Journal on Applied Mathematics, 73(4):1513–1532, 2013. 1.5, 2, 2.3, 5
2013
-
[42]
Further notes on the basic reproduction number
P Van den Driessche and James Watmough. Further notes on the basic reproduction number. In Mathematical epidemiology, pages 159–178. Springer, 2008. 1.5
2008
-
[43]
Reproduction numbers and sub-threshold endemic equilibria for compartmental models of disease transmission.Mathematical biosciences, 180(1-2):29– 48, 2002
Pauline Van den Driessche and James Watmough. Reproduction numbers and sub-threshold endemic equilibria for compartmental models of disease transmission.Mathematical biosciences, 180(1-2):29– 48, 2002. 1.5, 2, 5
2002
-
[44]
Prentice-Hall, 1962
Richard S Varga.Matrix iterative analysis: Englewood Cliffs. Prentice-Hall, 1962. 1, 1.5, 5
1962
-
[45]
Global stability of first order endotactic reaction systems.arXiv preprint arXiv:2409.01598, 2024
Chuang Xu. Global stability of first order endotactic reaction systems.arXiv preprint arXiv:2409.01598, 2024. 1.1
-
[46]
Applications of the poincar ´e–hopf theorem: Epidemic models and lotka–volterra systems.IEEE Transactions on Automatic Control, 67(4):1609– 1624, 2021
Mengbin Ye, Ji Liu, Brian DO Anderson, and Ming Cao. Applications of the poincar ´e–hopf theorem: Epidemic models and lotka–volterra systems.IEEE Transactions on Automatic Control, 67(4):1609– 1624, 2021. 1.5
2021
-
[47]
Mathematical analysis of chemical reaction systems.Israel Journal of Chemistry, 58(6-7):733–741, 2018
Polly Y Yu and Gheorghe Craciun. Mathematical analysis of chemical reaction systems.Israel Journal of Chemistry, 58(6-7):733–741, 2018. 1.1
2018
-
[48]
Xiaoyu Zhang, Zhou Fang, and Chuanhou Gao. Revisiting persistence of chemical reaction networks through Lyapunov function partial differential equations.arXiv preprint arXiv:1810.00225, 2018. 1.1 36
work page internal anchor Pith review Pith/arXiv arXiv 2018
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