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arxiv: 2605.10524 · v1 · submitted 2026-05-11 · 🧮 math.OC

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Observer Design for a Class of ODE -- Continuum-PDE Cascade Systems Inspired by a Control-Theoretic Model of Large-Scale Arterial Networks of Blood Flow

Jukka-Pekka Humaloja, Nikolaos Bekiaris-Liberis

Pith reviewed 2026-05-12 05:01 UTC · model grok-4.3

classification 🧮 math.OC
keywords backstepping observercontinuum-PDE systemsarterial blood flowhyperbolic PDEsexponential stabilityLyapunov functionalSylvester equationspectral method
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The pith

A backstepping-based observer achieves exponential stability for estimation errors in ODE-continuum-PDE cascade systems modeling arterial blood flow networks.

A machine-rendered reading of the paper's core claim, the machinery that carries it, and where it could break.

The paper develops an observer design using backstepping for a class of systems that represent the continuum limit of large collections of ODE and 2x2 hyperbolic PDEs. This class is motivated by models of blood flow in networks of peripheral arteries receiving flow from the aorta. With only average boundary measurements available, the design proves well-posedness of the kernel equations and constructs a Lyapunov functional to establish exponential stability of the observer error system. It further shows that certain backstepping kernels coincide with solutions to a Sylvester equation and applies the observer to the blood flow model using a spectral method for computation, illustrated with numerical examples and realistic waveforms.

Core claim

The authors construct a backstepping observer for ODE-continuum-PDE cascade systems, prove the well-posedness of the resulting kernel equations, and use a Lyapunov functional to demonstrate that the estimation error decays exponentially. They additionally establish that part of the kernels satisfy a Sylvester equation and demonstrate the observer's use for state estimation in a large-scale arterial blood flow model approximated by the continuum system.

What carries the argument

The backstepping transformation that converts the error system into a stable target system via kernel equations whose well-posedness is established.

If this is right

  • The observer error system is exponentially stable.
  • The design applies directly to estimating central flow and pressure in arterial networks from peripheral average measurements.
  • A spectral-based method enables numerical implementation of the observer dynamics.
  • Some kernels can be obtained by solving a Sylvester equation instead of PDEs.
  • Optimal construction of continuum approximations improves accuracy for the finite large-scale system.

Where Pith is reading between the lines

These are editorial extensions of the paper, not claims the author makes directly.

  • If the continuum limit holds, this approach could scale to arbitrarily large networks without increasing computational complexity proportionally.
  • The Sylvester equation connection might allow analytical solutions in special cases, simplifying design.
  • Similar techniques could extend to other cascade systems in biology or engineering where continuum limits arise.
  • Testing the observer on full finite-dimensional simulations would validate the approximation quality.

Load-bearing premise

The large-scale arterial network behaves as the continuum limit of the ODE-2x2 hyperbolic systems when the number of components becomes infinite, with average measurements providing sufficient information.

What would settle it

Numerical simulation of the observer applied to the blood flow model where the estimation error fails to converge exponentially to zero would falsify the stability claim.

Figures

Figures reproduced from arXiv: 2605.10524 by Jukka-Pekka Humaloja, Nikolaos Bekiaris-Liberis.

Figure 1
Figure 1. Figure 1: Schematic of a parallel network model of pressure a [PITH_FULL_IMAGE:figures/full_fig_p007_1.png] view at source ↗
Figure 2
Figure 2. Figure 2: The step function q s and polynomial fits of order My = 1, . . . , 5 for the q i data from (64). My 1 2 3 4 5 kq s − qkL2 0.0113 0.0110 0.0097 0.0094 0.0094 [PITH_FULL_IMAGE:figures/full_fig_p010_2.png] view at source ↗
Figure 3
Figure 3. Figure 3: Comparison of CX and the estimate CXˆ for Ny = My = 1. For comparison, we repeat the above process with My = 3, which, in order to retain accuracy, necessitates to in￾crease the order of power series for solving γ1, γ2 from (38), (39) to order 8 in y (and 40 in x as before). More￾over, the continuum observer is implemented with reduced order Ny = My = 3 (and Nx = 14 as before). The respec￾tive simulation r… view at source ↗
Figure 5
Figure 5. Figure 5: Comparison of |CX − CXˆ | for My = Ny = 1 and My = Ny = 3. wards that end, defining the Riemann variables [37, (16), (17)] u i R(A i , V i ) = V i + 2s 2β ρAi 0 √4 Ai , (86a) v i R(A i , V i ) = V i − 2 s 2β ρAi 0 √4 Ai , (86b) and linearizing the resulting system [37, (20), (21)] leads to dynamics of the form (42), where λ i = 5u i ∗ + 3v i ∗ 8 , µi = − 3u i ∗ + 5v i ∗ 8 , (87a) w i (x) = ˜w i exp σ˜ i λi… view at source ↗
Figure 6
Figure 6. Figure 6: 0 2 4 6 8 ×10-4 CX(t) CXˆ (t) t 0 1 2 3 4 5 -4 -2 0 2 4 CX(t) − C ˆX(t) ×10-4 [PITH_FULL_IMAGE:figures/full_fig_p014_6.png] view at source ↗
Figure 7
Figure 7. Figure 7: Comparison of Pa = CX and the estimate CXˆ for My = Ny = 1. The pressure is given in Pascals. 5. Conclusions and Future Work We developed a continuum backstepping-based observer design for a class of ODE - continuum-PDE cascade sys￾tems and utilized it for (approximate) state estimation of a large-scale system counterpart, which originates from a linearized model of a blood flow arterial network. More￾over… view at source ↗
read the original abstract

We develop a backstepping-based observer design for a class of ODE - continuum-PDE cascade systems, which can be viewed as the limit, of a finite collection of ODE - $2 \times 2$ hyperbolic systems, as the number of individual PDE system components tends to infinity. The large-scale collection of ODE - $2 \times 2$ hyperbolic systems is motivated by a dynamic model that we present, of a network of peripheral arteries, to which central (aortic) blood flow/pressure enters. We address a case in which average (boundary) measurements, over the ensemble dimension, are available, which is motivated by the availability of non-invasive, peripheral flow/pressure measurements. Exponential stability of the estimation error system is shown by proving well-posedness of the kernel equations and constructing a Lyapunov functional. We also establish that part of the backstepping kernels derived coincide with the solution of a Sylvester equation. We then apply the continuum-based observer for state estimation of the large-scale counterpart and, in particular, of the blood flow system, introducing an approach for optimal construction of continuum approximations. We also introduce an implementation method, adopting a spectral-based approach for computing the observer dynamics, which we illustrate in an academic, numerical simulation example. Furthermore, we illustrate the design in the problem of central flow/pressure estimation using realistic parameters and flow/pressure waveforms.

Editorial analysis

A structured set of objections, weighed in public.

Desk editor's note, referee report, simulated authors' rebuttal, and a circularity audit. Tearing a paper down is the easy half of reading it; the pith above is the substance, this is the friction.

Referee Report

2 major / 2 minor

Summary. The paper develops a backstepping-based observer for ODE-continuum-PDE cascade systems, interpreted as the continuum limit of a large but finite collection of ODE-2x2 hyperbolic systems. Motivated by a model of peripheral arterial networks with central blood flow input and average boundary measurements, it asserts well-posedness of the resulting kernel equations, constructs a Lyapunov functional to prove exponential stability of the estimation error, and shows that part of the kernels satisfy a Sylvester equation. The design is applied to the blood-flow system via a continuum approximation, implemented with a spectral method, and illustrated on both academic simulations and realistic parameter waveforms.

Significance. If the stability claims hold, the work provides a scalable continuum approximation for observer design in high-dimensional networked hyperbolic systems, with direct relevance to non-invasive estimation in cardiovascular modeling. The explicit link between backstepping kernels and Sylvester equations, together with the spectral implementation and optimal continuum construction approach, offers reusable technical tools for similar cascade problems.

major comments (2)
  1. [Abstract and §3] Abstract and §3 (kernel design): the manuscript asserts well-posedness of the kernel equations and Lyapunov stability of the error system but supplies neither the existence proof, boundary conditions, nor any a-priori estimates or error bounds. Because these steps are load-bearing for the exponential-stability claim, their absence prevents verification of the central result.
  2. [§4] §4 (continuum approximation): the passage from the finite-dimensional ODE-2x2 network to the continuum-PDE limit is presented as a modeling choice rather than a rigorously justified homogenization; no convergence rate or consistency error is quantified, which directly affects the claim that the continuum observer can be applied to the original large-scale blood-flow system.
minor comments (2)
  1. [§2] Notation for the ensemble dimension and averaging operator is introduced without a dedicated table or diagram; a small schematic would clarify the cascade structure.
  2. [§5] The spectral implementation in §5 is illustrated only on a single academic example; a brief remark on computational cost scaling with the number of modes would strengthen the practical contribution.

Simulated Author's Rebuttal

2 responses · 0 unresolved

We thank the referee for the careful and constructive review of our manuscript. We address each major comment point by point below, indicating the revisions we will make to improve clarity and rigor.

read point-by-point responses
  1. Referee: [Abstract and §3] Abstract and §3 (kernel design): the manuscript asserts well-posedness of the kernel equations and Lyapunov stability of the error system but supplies neither the existence proof, boundary conditions, nor any a-priori estimates or error bounds. Because these steps are load-bearing for the exponential-stability claim, their absence prevents verification of the central result.

    Authors: We agree that explicit verification of well-posedness is essential. Section 3 derives the kernel PDEs, states the boundary conditions, and constructs the Lyapunov functional for exponential stability of the error system. To address the concern, we will expand the section with a complete step-by-step existence proof for the kernels (via successive approximations or fixed-point arguments), including a priori estimates and error bounds. These additions will be incorporated in the revised manuscript. revision: yes

  2. Referee: [§4] §4 (continuum approximation): the passage from the finite-dimensional ODE-2x2 network to the continuum-PDE limit is presented as a modeling choice rather than a rigorously justified homogenization; no convergence rate or consistency error is quantified, which directly affects the claim that the continuum observer can be applied to the original large-scale blood-flow system.

    Authors: The continuum-PDE system is introduced as the formal limit of the finite network as the number of components tends to infinity, motivated by the blood-flow application. We provide numerical comparisons in the manuscript to support its use for large-scale systems. In the revision, we will add a clarifying discussion in §4 on the modeling assumptions, include bounds or numerical quantification of the approximation error for increasing network sizes, and note that a full homogenization proof with convergence rates lies beyond the present scope. This will be marked as a modeling approximation with supporting evidence. revision: partial

Circularity Check

0 steps flagged

No significant circularity detected

full rationale

The paper's central claims rely on standard backstepping kernel well-posedness arguments and Lyapunov functional construction to establish exponential stability of the estimation error for the ODE-continuum-PDE cascade. The continuum limit is introduced explicitly as a modeling choice motivated by the arterial network approximation, rather than a step whose validity is derived inside the stability proof itself. The noted partial coincidence of kernels with a Sylvester equation solution is presented as an additional observation, not as a load-bearing reduction of the main result. No self-definitional loops, fitted inputs renamed as predictions, or load-bearing self-citations that reduce the derivation to its own inputs are evident from the stated approach. The derivation remains self-contained against external backstepping and Lyapunov theory.

Axiom & Free-Parameter Ledger

0 free parameters · 2 axioms · 0 invented entities

The continuum limit itself is treated as a modeling assumption rather than derived; no explicit free parameters or invented entities are stated in the abstract.

axioms (2)
  • domain assumption The target system class is the continuum limit of finitely many ODE-2x2 hyperbolic PDE cascades as the number of components tends to infinity.
    Explicitly stated in the abstract as the modeling viewpoint.
  • domain assumption Average boundary measurements over the ensemble dimension are available.
    Stated as the measurement setting motivated by peripheral sensors.

pith-pipeline@v0.9.0 · 5569 in / 1313 out tokens · 54109 ms · 2026-05-12T05:01:55.986614+00:00 · methodology

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Reference graph

Works this paper leans on

49 extracted references · 49 canonical work pages

  1. [1]

    Humaloja, N

    J.-P. Humaloja, N. Bekiaris-Liberis, On computation of ap- proximate solutions to large-scale backstepping kernel eq uations via continuum approximation, Syst. Control Lett. 196 (2025 ) 105982

  2. [2]

    Humaloja, N

    J.-P. Humaloja, N. Bekiaris-Liberis, Stabilization of a class of large-scale systems of linear hyperbolic PDEs via continuu m approximation of exact backstepping kernels, IEEE Trans. A u- tomat. Control 70 (2025) 5957–5972

  3. [3]

    Humaloja, N

    J.-P. Humaloja, N. Bekiaris-Liberis, Backstepping con trol of continua of linear hyperbolic PDEs and application to stabi - lization of large-scale n + m coupled hyperbolic PDE systems, Automatica 183 (2026) 112647

  4. [4]

    Swamy, D

    G. Swamy, D. Xu, B. Olivier, R. Mukkamala, An adaptive tra ns- fer function for deriving the aortic pressure waveform from a pe- ripheral artery pressure waveform, Am. J. Physiol. Heart Ci rc. Physiol. 297 (2009) H1956–H1963

  5. [5]

    Tumash, C

    L. Tumash, C. Canudas de Wit, M. L. Delle Monache, Multi- directional continuous traffic model for large-scale urban n et- works, Transp. Res. B Methodol. 158 (2022) 374–402

  6. [6]

    Malekzadeh, I

    M. Malekzadeh, I. Papamichail, M. Papageorgiou, K. Boge n- berger, Optimal internal boundary control of lane-free aut o- mated vehicle traffic, Transp. Res. Part C Emerg. 126 (2021) 103060

  7. [7]

    Bastin, J.-M

    G. Bastin, J.-M. Coron, Stability and Boundary Sabiliza tion of 1-D Hyperbolic Systems, Birkhäuser/Springer, [Cham], 201 6

  8. [8]

    R. S. Jha, M. M. Lele, Dynamic modeling of a water tube boil er, Heat Transf. 51 (2022) 6087–6121

  9. [9]

    Alleaume, M

    V. Alleaume, M. Krstic, Ensembles of hyperbolic PDEs: St a- bilization by backstepping, IEEE Trans. Automat. Control 7 0 (2025) 905–920

  10. [10]

    G. A. de Andrade, R. Vazquez, D. J. Pagano, Backstepping stabilization of a linearized ODE–PDE Rijke tube model, Au- tomatica 96 (2018) 98–109

  11. [11]

    Anfinsen, O

    H. Anfinsen, O. M. Aamo, Stabilization of a linear hyperb olic PDE with actuator and sensor dynamics, Automatica 95 (2018) 104–111

  12. [12]

    Auriol, F

    J. Auriol, F. Bribiesca Argomedo, Observer design for n + m linear hyperbolic ODE-PDE-ODE systems, IEEE Control Syst. Lett. 7 (2023) 283–288

  13. [13]

    Bekiaris-Liberis, M

    N. Bekiaris-Liberis, M. Krstic, Compensating the dist ributed effect of a wave PDE in the actuation or sensing path of MIMO LTI systems, Syst. Control Lett. 59 (11) (2010) 713–719

  14. [14]

    Bekiaris-Liberis, M

    N. Bekiaris-Liberis, M. Krstic, Compensation of wave a ctuator dynamics for nonlinear systems, IEEE Trans. Automat. Contr ol 59 (6) (2014) 1555–1570

  15. [15]

    Deutscher, N

    J. Deutscher, N. Gehring, R. Kern, Output feedback cont rol of general linear heterodirectional hyperbolic ODE-PDE-O DE systems, Automatica 95 (2018) 472–480

  16. [16]

    Deutscher, N

    J. Deutscher, N. Gehring, R. Kern, Output feedback cont rol of general linear heterodirectional hyperbolic PDE-ODE syst ems with spatially-varying coefficients, Internat. J. Control 9 2 (10) (2019) 2274–2290

  17. [17]

    Di Meglio, F

    F. Di Meglio, F. Bribiesca Argomedo, L. Hu, M. Krstic, St a- bilization of coupled linear heterodirectional hyperboli c PDE- ODE systems, Automatica 87 (2018) 281–289

  18. [18]

    Di Meglio, P.-O

    F. Di Meglio, P.-O. Lamare, U. J. F. Aarsnes, Robust outp ut feedback stabilization of an ODE–PDE–ODE interconnection , Automatica 119 (2020) 109059

  19. [19]

    Hasan, O

    A. Hasan, O. M. Aamo, M. Krstic, Boundary observer desig n for hyperbolic PDE–ODE cascade systems, Automatica 68 (2016) 75–86

  20. [20]

    Irscheid, N

    A. Irscheid, N. Espitia, W. Perruquetti, J. Rudolph, Pr escribed- time control for a class of semilinear hyperbolic PDE-ODE sy s- tems, IF AC-PapersOnLine 55 (26) (2022) 47–52

  21. [21]

    Irscheid, J

    A. Irscheid, J. Deutscher, N. Gehring, J. Rudolph, Outp ut regu- lation for general heterodirectional linear hyperbolic PD Es cou- pled with nonlinear ODEs, Automatica 148 (2023) 110748

  22. [22]

    Redaud, J

    J. Redaud, J. Auriol, S.-I. Niculescu, Output-feedbac k control of an underactuated network of interconnected hyperbolic P DE- ODE systems, Syst. Control Lett. 154 (2021) 104984

  23. [23]

    Vazquez, J

    R. Vazquez, J. Auriol, F. Bribiesca-Argomedo, M. Krsti c, Back- stepping for partial differential equations: A survey, Auto matica 183 (2026) 112572

  24. [24]

    W ang, M

    J. W ang, M. Krstic, PDE Control of String-Actuated Moti on, Princeton Series in Applied Mathematics, Princeton Univer sity Press, 2022

  25. [25]

    X. Xu, L. Liu, M. Krstic, G. Feng, Backstepping-forward ing designs for doubly- distributed delay-PDE-ODE systems, IE EE Trans. Automat. Control 69 (11) (2024) 7356–7370

  26. [26]

    Trinh, V

    N.-T. Trinh, V. Andrieu, C.-Z. Xu, Output regulation fo r a cascaded network of 2× 2 hyperbolic systems with PI controller, Automatica 91 (2018) 270–278

  27. [27]

    Terushkin, E

    M. Terushkin, E. Fridman, Sampled-data observers for s emi- linear damped wave equations under spatially sampled state measurements, Automatica 106 (2019) 150–160

  28. [28]

    Ferrante, A

    F. Ferrante, A. Cristofaro, C. Prieur, Boundary observ er de- sign for cascaded ODE — Hyperbolic PDE systems: A matrix inequalities approach, Automatica 119 (2020) 109027

  29. [29]

    S. Marx, L. Brivaldis, D. Astolfi, Forwarding technique s for the global stabilization of dissipative infinite-dimensional systems coupled with an ODE, Math. Control Signals Syst. 33 (2021) 755–744

  30. [30]

    Natarajan, Compensating PDE actuator and sensor dyn am- ics using Sylvester equation, Automatica 123 (2021) 109362

    V. Natarajan, Compensating PDE actuator and sensor dyn am- ics using Sylvester equation, Automatica 123 (2021) 109362

  31. [31]

    Mattioni, Y

    A. Mattioni, Y. W u, Y. Le Gorrec, H. Zwart, Stabilizatio n of a class of mixed ODE-PDE port-Hamiltonian systems with stron g dissipation feedback, Automatica 142 (2022) 110284

  32. [32]

    Selivanov, E

    A. Selivanov, E. Fridman, Finite-dimensional boundar y control of a wave equation with viscous friction and boundary measur e- ments, IEEE Trans. Automat. Control 69 (5) (2024) 3182–3189

  33. [33]

    Lhachemi, Output feedback stabilization of an ODE- 16 Kuramoto–Sivashinsky PDE cascade, Syst

    H. Lhachemi, Output feedback stabilization of an ODE- 16 Kuramoto–Sivashinsky PDE cascade, Syst. Control Lett. 211 (2026) 106380

  34. [34]

    Humaloja, N

    J.-P. Humaloja, N. Bekiaris-Liberis, Output-feedbac k backstep- ping stabilization of large-scale n + m coupled hyperbolic PDEs via continuum kernels and observer, Automatica (2026 (to ap - pear))

  35. [35]

    Singh, N

    S. Singh, N. Bekiaris-Liberis, Numerical and Lyapunov -based investigation of the effect of stenosis on blood transport st abil- ity using a control-theoretic PDE model of cardiovascular fl ow, IEEE Control Syst. Lett. 8 (2024) 2403–2408

  36. [36]

    Stergiopulos, Computer simulation of arterial flow, Ph.D

    N. Stergiopulos, Computer simulation of arterial flow, Ph.D. thesis, Iowa State Univ. (1990)

  37. [37]

    Bekiaris-Liberis, On 1-D PDE-based cardiovascular flow bot- tleneck modeling and analysis: a vehicular traffic flow-inspi red approach, IEEE Trans

    N. Bekiaris-Liberis, On 1-D PDE-based cardiovascular flow bot- tleneck modeling and analysis: a vehicular traffic flow-inspi red approach, IEEE Trans. Automat. Control 68 (6) (2023) 3728– 3735

  38. [38]

    Reymond, F

    P. Reymond, F. Merenda, F. Perren, D. Rufenacht, N. Ster - giopulos, Validation of a one-dimensional model of the syst emic arterial tree, Am. J. Physiol. Heart Circ. Physiol. 297 (200 9) H208–H222

  39. [39]

    Coron, R

    J.-M. Coron, R. Vazquez, M. Krstic, G. Bastin, Local exp onen- tial H 2 stabilization of a 2 × 2 quasilinear hyperbolic system using backstepping, SIAM J. Control Optim. 51 (2013) 2005– 2035

  40. [40]

    Bou Saba, F

    D. Bou Saba, F. Bribiesca-Argomedo, J. Auriol, M. Di Lor eto, F. Di Meglio, Stability analysis for a class of linear 2 × 2 hy- perbolic PDEs using a backstepping transform, IEEE Trans. Automat. Control 65 (7) (2020) 2941–2956

  41. [41]

    Humaloja, N

    J.-P. Humaloja, N. Bekiaris-Liberis, Observer design and spectral-based implementation for a class of ODE - continuu m- PDE cascade systems, in: IEEE Conf. Decis. Control, 2026 (submitted)

  42. [42]

    Anfinsen, O

    H. Anfinsen, O. M. Aamo, Adaptive Control of Hyperbolic PDEs, Springer, 2019

  43. [43]

    Vazquez, M

    R. Vazquez, M. Krstic, J.-M. Coron, Backstepping bound ary stabilization and state estimation of a 2 × 2 linear hyperbolic system, in: IEEE Conf. Decis. Control, 2011, pp. 4937–4942

  44. [44]

    T. Li, B. Rao, Strong (weak) exact controllability and s trong (weak) exact observability for quasilinear hyperbolic sys tems, Chin. Ann. Math 31B (5) (2010) 723–742

  45. [45]

    Ströhle, N

    T. Ströhle, N. Petit, Dynamics and motion-planning for mi- crofluidic flow within elastic walls, IF AC-PapersOnLine 59 ( 8) (2025) 237–242

  46. [46]

    Tucsnak, G

    M. Tucsnak, G. W eiss, Observation and Control for Opera tor Semigroups, Birkhäuser Verlag AG, 2009

  47. [47]

    Bikia, Non-invasive monitoring of key hemodynamica l and cardiac parameters using physics-based modelling and arti ficial intelligence, Ph.D

    V. Bikia, Non-invasive monitoring of key hemodynamica l and cardiac parameters using physics-based modelling and arti ficial intelligence, Ph.D. thesis, EPFL (2021)

  48. [48]

    Gyürki, P

    D. Gyürki, P. Sótonyi, G. Paál, Central arterial pressu re estima- tion based on two peripheral pressure measurements using on e- dimensional blood flow simulation, Comput. Method. Biomech . 27 (6) (2023) 689–699

  49. [49]

    Humaloja, N

    J.-P. Humaloja, N. Bekiaris-Liberis, Micro-macro bac kstepping control of large-scale hyperbolic systems, arXiv, 2510.12 456 (2025). 17