YANNs: Y-wise Affine Neural Networks for Exact and Efficient Representations of Piecewise Linear Functions
Pith reviewed 2026-05-22 16:22 UTC · model grok-4.3
The pith
YANNs give exact training-free neural representations of piecewise affine functions over polytopic regions.
A machine-rendered reading of the paper's core claim, the machinery that carries it, and where it could break.
Core claim
YANNs achieve an exact, training-free representation of piecewise affine functions with polytopic subdomains whose parameters can be computed directly from the original function description without optimization or data fitting. When the same construction is applied to the piecewise affine optimal control law obtained from multi-parametric model predictive control, the resulting YANN controller retains recursive feasibility and stability guarantees and evaluates substantially faster than traditional piecewise affine calculations.
What carries the argument
The YANN architecture itself, a feed-forward network whose layers are arranged to encode each affine piece exactly over its polytopic subdomain while enforcing continuity across boundaries.
If this is right
- Any piecewise affine function over polytopic subdomains can be replaced by an equivalent YANN whose parameters are obtained by direct calculation.
- A multi-parametric MPC law encoded as a YANN controller inherits recursive feasibility and closed-loop stability from the original law.
- Real-time evaluation of the control law becomes faster than explicit enumeration or binary search over the polytopic regions.
- The construction scales with the number of subdomains and the dimension of the state and input spaces.
Where Pith is reading between the lines
- YANNs could serve as an interpretable, safety-preserving bridge between explicit MPC and learned controllers in embedded hardware.
- The same exact-representation technique might be tested on hybrid system models whose mode switches are also polytopic.
- Because the mapping from original description to YANN weights is direct, one could derive closed-form expressions for the network size in terms of the number of regions.
Load-bearing premise
Any piecewise affine function over polytopic subdomains admits an exact YANN representation whose parameters are obtained by direct calculation from the function description.
What would settle it
A concrete piecewise affine function on polytopes for which no choice of YANN weights and biases computed directly from its description reproduces the function values exactly on every subdomain.
Figures
read the original abstract
This work formally introduces Y-wise Affine Neural Networks (YANNs), a fully-explainable network architecture that continuously and efficiently represent piecewise affine functions with polytopic subdomains. Following from the proofs, it is shown that the development of YANNs requires no training to achieve the functionally equivalent representation. YANNs thus maintain all mathematical properties of the original formulations. Multi-parametric model predictive control is utilized as an application showcase of YANNs, which theoretically computes optimal control laws as a piecewise affine function of states, outputs, setpoints, and disturbances. With the exact representation of multi-parametric control laws, YANNs retain essential control-theoretic guarantees such as recursive feasibility and stability. This sets YANNs apart from the existing works which apply neural networks for approximating optimal control laws instead of exactly representing them. By optimizing the inference speed of the networks, YANNs can evaluate substantially faster in real-time compared to traditional piecewise affine function calculations. Numerical case studies are presented to demonstrate the algorithmic scalability with respect to the input/output dimensions and the number of subdomains. YANNs represent a significant advancement in control as the first neural network-based controller that inherently ensures both feasibility and stability. Future applications can leverage them as an efficient and interpretable starting point for data-driven modeling/control.
Editorial analysis
A structured set of objections, weighed in public.
Referee Report
Summary. The paper introduces Y-wise Affine Neural Networks (YANNs), a neural architecture designed to exactly represent continuous piecewise-affine (PWA) functions whose domains are unions of polytopes. Sections 3.2–3.4 supply constructive, training-free proofs that the network weights and biases are obtained by direct algebraic substitution from the facet inequalities of each polytope and the coefficients of the local affine maps. The resulting YANN is then substituted for the explicit PWA control law in multi-parametric MPC; because the representation is identical, recursive feasibility and stability guarantees carry over verbatim. Numerical case studies illustrate scalability with respect to state dimension and number of regions, and inference is reported to be faster than conventional PWA evaluation.
Significance. If the constructive proofs are correct, the work supplies the first neural-network controller that is both exactly equivalent to a PWA law and therefore inherits all stability and feasibility certificates of the original mp-MPC formulation. This is a substantive advance for real-time explicit MPC on embedded hardware, where the combination of interpretability, absence of training, and faster evaluation could be practically useful.
major comments (2)
- [§3.3] §3.3, after Eq. (12): the proof that the YANN output is identical to the original PWA function assumes that the polytopes form a partition (no overlaps and full coverage of the domain). The manuscript should explicitly state whether the construction remains exact when the polytopes only cover a subset of the state space or when they overlap on sets of measure zero.
- [§4.2] §4.2, Table 2: the reported speed-up factors are given only for the forward pass; the paper should also report the one-time cost of constructing the YANN parameters from the mp-MPC solution and compare total wall-clock time (construction + inference) against the conventional explicit PWA controller for the same number of regions.
minor comments (3)
- [§2] The notation for the Y-wise activation function is introduced in §2 but never given an explicit mathematical definition; a single displayed equation would remove ambiguity.
- [Figure 3] Figure 3 caption states that the network has “no hidden layers,” yet the diagram shows two layers of Y-wise units; the caption should be corrected to “two Y-wise layers” or the diagram revised.
- [References] Reference list is missing the foundational mp-MPC papers (e.g., Bemporad et al., 2002) that supply the stability theorems invoked in §4.1.
Simulated Author's Rebuttal
We thank the referee for the careful review and constructive feedback. We address the major comments point by point below.
read point-by-point responses
-
Referee: [§3.3] §3.3, after Eq. (12): the proof that the YANN output is identical to the original PWA function assumes that the polytopes form a partition (no overlaps and full coverage of the domain). The manuscript should explicitly state whether the construction remains exact when the polytopes only cover a subset of the state space or when they overlap on sets of measure zero.
Authors: We appreciate this observation. The proofs in §3.3 are developed under the assumption that the polytopes constitute a partition of the domain, which is the typical setting for continuous PWA functions arising from mp-MPC. Overlaps, when present, are confined to boundaries of measure zero, where the continuity of the PWA function ensures consistency. When the polytopes cover only a subset of the state space, the YANN exactly reproduces the PWA function on the covered region. We will revise the manuscript to explicitly state these conditions and clarify the exactness in such scenarios. revision: yes
-
Referee: [§4.2] §4.2, Table 2: the reported speed-up factors are given only for the forward pass; the paper should also report the one-time cost of constructing the YANN parameters from the mp-MPC solution and compare total wall-clock time (construction + inference) against the conventional explicit PWA controller for the same number of regions.
Authors: We agree that reporting the construction cost is important for a fair comparison. The YANN parameters are obtained via direct algebraic substitution, which is computationally inexpensive and performed offline. In the revised version, we will include the construction times in Table 2 or an additional table and provide a comparison of total wall-clock time (construction plus inference) versus the standard explicit PWA controller. revision: yes
Circularity Check
No significant circularity; derivation is a direct constructive equivalence
full rationale
The paper supplies explicit constructive proofs (Sections 3.2–3.4) that any continuous PWA function over a finite set of polytopes admits an exact YANN representation obtained by direct algebraic substitution of the facet inequalities and local affine coefficients into the network weights and biases. No optimization, data fitting, or iterative procedure is used, so the resulting network computes identically the same function and all control-theoretic properties transfer verbatim. The central claim is therefore a definitional equivalence constructed from the input PWA description rather than a prediction or fit that reduces to itself. No self-citation is load-bearing for the proofs, and the architecture is presented as newly defined to achieve this exact match.
Axiom & Free-Parameter Ledger
axioms (1)
- domain assumption Any piecewise affine function defined over polytopic subdomains admits an exact YANN representation that can be constructed without training or optimization.
Lean theorems connected to this paper
-
IndisputableMonolith/Cost/FunctionalEquation.leanwashburn_uniqueness_aczel unclear?
unclearRelation between the paper passage and the cited Recognition theorem.
Theorem 17 … five-layer neural network … given that no subdomains overlap … YANN architecture … layers one through three are the constraint checking section … layers four through five are the function evaluation section
-
IndisputableMonolith/Foundation/RealityFromDistinction.leanreality_from_one_distinction unclear?
unclearRelation between the paper passage and the cited Recognition theorem.
Lemma 2 … two-layer neural network … BSF … ReLU … indicator function for a system of q linear inequalities
What do these tags mean?
- matches
- The paper's claim is directly supported by a theorem in the formal canon.
- supports
- The theorem supports part of the paper's argument, but the paper may add assumptions or extra steps.
- extends
- The paper goes beyond the formal theorem; the theorem is a base layer rather than the whole result.
- uses
- The paper appears to rely on the theorem as machinery.
- contradicts
- The paper's claim conflicts with a theorem or certificate in the canon.
- unclear
- Pith found a possible connection, but the passage is too broad, indirect, or ambiguous to say the theorem truly supports the claim.
Forward citations
Cited by 2 Pith papers
-
Reinforcement Learning-based Control via Y-wise Affine Neural Networks (YANNs)
YANN-RL initializes RL actor and critic networks with explicit multi-parametric linear MPC solutions via YANNs to start from linear optimal control performance and then learn nonlinear policies through online interaction.
-
Reinforcement Learning-based Control via Y-wise Affine Neural Networks: Comparative Case Studies for Chemical Processes
YANN-RL is tested on three PC-Gym chemical process case studies, showing reduced training time and near-NMPC performance compared to PPO, SAC, DDPG, and TD3.
Reference graph
Works this paper leans on
-
[1]
Multilayer feedforward networks are universal approximators
Kurt Hornik, Maxwell Stinchcombe, and Halbert White. Multilayer feedforward networks are universal approximators. Neural Networks , 2(5):359–366, January 1989
work page 1989
-
[2]
Lee, Srinivas Rangarajan, Leo Chiang, Bhushan Gopaluni, Artur M
Prodromos Daoutidis, Jay H. Lee, Srinivas Rangarajan, Leo Chiang, Bhushan Gopaluni, Artur M. Schweidtmann, Iiro Harjunkoski, Mehmet Mercang¨ oz, Ali Mesbah, Fani Boukouvala, Fernando V. Lima, Antonio del Rio Chanona, and Christos Georgakis. Machine learning in process systems engineering: Challenges and opportunities. Computers & Chem- ical Engineering, 1...
work page 2024
-
[3]
Niknezhad, Faisal Khan, Efstratios N
Austin Braniff, Sahithi Srijana Akundi, Yuanxing Liu, Beatriz Dantas, Shayan S. Niknezhad, Faisal Khan, Efstratios N. Pistikopoulos, and Yuhe Tian. Real-time process safety and systems decision-making toward safe and smart chemical manufacturing. Digital Chemical Engineering , 15:100227, June 2025
work page 2025
-
[4]
J´ an Drgoˇ na, Karol Kiˇ s, Aaron Tuor, Draguna Vrabie, and Martin Klauˇ co. Differentiable predictive control: Deep learning alternative to explicit model predictive control for unknown nonlinear systems. Journal of Pro- cess Control, 116:80–92, August 2022
work page 2022
-
[5]
Yujia Wang, Xinji Zhu, and Zhe Wu. A tutorial review of policy iteration methods in reinforcement learning for nonlinear optimal control. Digital Chemical Engineering, 15:100231, June 2025
work page 2025
-
[6]
Surrogate-Based Optimization Tech- niques for Process Systems Engineering, December 2024
Mathias Neufang, Emma Pajak, Damien van de Berg, Ye Seol Lee, and Ehecatl Antonio del Rio Chanona. Surrogate-Based Optimization Tech- niques for Process Systems Engineering, December 2024
work page 2024
-
[7]
Haeun Yoo, Ha Eun Byun, Dongho Han, and Jay H. Lee. Reinforcement learning for batch process control: Review and perspectives. Annual Re- views in Control , 52:108–119, January 2021
work page 2021
-
[8]
Austin Braniff and Yuhe Tian. A hierarchical multi-parametric program- ming approach for dynamic risk-based model predictive quality control. Control Engineering Practice, 152:106062, November 2024
work page 2024
-
[9]
Justin Katz, Iosif Pappas, Styliani Avraamidou, and Efstratios N. Pis- tikopoulos. The Integration of Explicit MPC and ReLU based Neural Networks. IFAC-PapersOnLine, 53(2):11350–11355, January 2020
work page 2020
-
[10]
Duo Xu, Rody Aerts, Petros Karamanakos, and Mircea Lazar. 31 Constraints-Informed Neural-Laguerre Approximation of Nonlinear MPC with Application in Power Electronics, September 2024
work page 2024
-
[11]
Model predictive control for systems with fast dynamics using inverse neural models
Marios Stogiannos, Alex Alexandridis, and Haralambos Sarimveis. Model predictive control for systems with fast dynamics using inverse neural models. ISA Transactions, 72:161–177, January 2018
work page 2018
-
[12]
Closed-loop optimisation of neural networks for the design of feedback policies under uncertainty
Evren Mert Turan and Johannes J¨ aschke. Closed-loop optimisation of neural networks for the design of feedback policies under uncertainty. Journal of Process Control, 133:103144, January 2024
work page 2024
-
[13]
Filippo Fabiani and Paul J. Goulart. Reliably-Stabilizing Piecewise-Affine Neural Network Controllers. IEEE Transactions on Automatic Control , 68(9):5201–5215, September 2023
work page 2023
-
[14]
Neural Network Optimal Feedback Control With Guaranteed Local Stability
Tenavi Nakamura-Zimmerer, Qi Gong, and Wei Kang. Neural Network Optimal Feedback Control With Guaranteed Local Stability. IEEE Open Journal of Control Systems , 1:210–222, 2022
work page 2022
-
[15]
Feng-Lei Fan, Jinjun Xiong, Mengzhou Li, and Ge Wang. On Inter- pretability of Artificial Neural Networks: A Survey.IEEE Transactions on Radiation and Plasma Medical Sciences , 5(6):741–760, November 2021
work page 2021
-
[16]
Interpreting Black-Box Models: A Review on Explainable Artificial Intelligence
Vikas Hassija, Vinay Chamola, Atmesh Mahapatra, Abhinandan Singal, Divyansh Goel, Kaizhu Huang, Simone Scardapane, Indro Spinelli, Mufti Mahmud, and Amir Hussain. Interpreting Black-Box Models: A Review on Explainable Artificial Intelligence. Cognitive Computation, 16(1):45– 74, January 2024
work page 2024
-
[17]
Nghiem, Thomas Beckers, Mahyar Fazlyab, En- rique Mallada, Colin Jones, Draguna Vrabie, Steven L
Jan Drgona, Truong X. Nghiem, Thomas Beckers, Mahyar Fazlyab, En- rique Mallada, Colin Jones, Draguna Vrabie, Steven L. Brunton, and Rolf Findeisen. Safe Physics-Informed Machine Learning for Dynamics and Control, April 2025
work page 2025
-
[18]
Pratyush Kumar, James B. Rawlings, and Stephen J. Wright. Indus- trial, large-scale model predictive control with structured neural net- works. Computers & Chemical Engineering , 150:107291, July 2021
work page 2021
-
[19]
Wells, Anastasia Niko- lakopoulou, Richard D
Hoang Hai Nguyen, Tim Zieger, Sandra C. Wells, Anastasia Niko- lakopoulou, Richard D. Braatz, and Rolf Findeisen. Stability Certifi- cates for Neural Network Learning-based Controllers using Robust Con- trol Theory. In 2021 American Control Conference (ACC) , pages 3564– 3569, May 2021
work page 2021
-
[20]
Andrea Tagliabue and Jonathan P. How. Efficient Deep Learning of Ro- bust Policies From MPC Using Imitation and Tube-Guided Data Aug- mentation. IEEE Transactions on Robotics, 40:4301–4321, 2024
work page 2024
-
[21]
Joel A. Paulson and Ali Mesbah. Approximate Closed-Loop Robust Model Predictive Control With Guaranteed Stability and Constraint Sat- isfaction. IEEE Control Systems Letters , 4(3):719–724, July 2020
work page 2020
-
[22]
Donti, Melrose Roderick, Mahyar Fazlyab, and J
Priya L. Donti, Melrose Roderick, Mahyar Fazlyab, and J. Zico Kolter. Enforcing robust control guarantees within neural network policies, Jan- uary 2021
work page 2021
-
[23]
Steven Chen, Kelsey Saulnier, Nikolay Atanasov, Daniel D. Lee, Vijay Kumar, George J. Pappas, and Manfred Morari. Approximating Explicit 32 Model Predictive Control Using Constrained Neural Networks. In 2018 Annual American Control Conference (ACC) , pages 1520–1527, June 2018
work page 2018
-
[24]
E. T. Maddalena, C. G. da S. Moraes, G. Waltrich, and C. N. Jones. A Neural Network Architecture to Learn Explicit MPC Controllers from Data. IFAC-PapersOnLine, 53(2):11362–11367, January 2020
work page 2020
-
[25]
Efficient Representation and Approx- imation of Model Predictive Control Laws via Deep Learning
Benjamin Karg and Sergio Lucia. Efficient Representation and Approx- imation of Model Predictive Control Laws via Deep Learning. IEEE Transactions on Cybernetics, 50(9):3866–3878, September 2020
work page 2020
-
[26]
Learning an Approximate Model Predictive Controller With Guarantees
Michael Hertneck, Johannes K¨ ohler, Sebastian Trimpe, and Frank Allg¨ ower. Learning an Approximate Model Predictive Controller With Guarantees. IEEE Control Systems Letters , 2(3):543–548, July 2018
work page 2018
-
[27]
Sydney M. Katz, Kyle D. Julian, Christopher A. Strong, and Mykel J. Kochenderfer. Generating probabilistic safety guarantees for neural net- work controllers. Machine Learning, 112(8):2903–2931, August 2023
work page 2023
-
[28]
Near- Optimal Rapid MPC Using Neural Networks: A Primal-Dual Policy Learning Framework
Xiaojing Zhang, Monimoy Bujarbaruah, and Francesco Borrelli. Near- Optimal Rapid MPC Using Neural Networks: A Primal-Dual Policy Learning Framework. IEEE Transactions on Control Systems Technology, 29(5):2102–2114, September 2021
work page 2021
-
[29]
W. Shaw Cortez, J. Drgona, A. Tuor, M. Halappanavar, and D. Vrabie. Differentiable Predictive Control with Safety Guarantees: A Control Bar- rier Function Approach. In 2022 IEEE 61st Conference on Decision and Control (CDC), pages 932–938, December 2022
work page 2022
-
[30]
Learning Constrained Parametric Differentiable Predictive Control Policies With Guaran- tees
J´ an Drgoˇ na, Aaron Tuor, and Draguna Vrabie. Learning Constrained Parametric Differentiable Predictive Control Policies With Guaran- tees. IEEE Transactions on Systems, Man, and Cybernetics: Systems , 54(6):3596–3607, June 2024
work page 2024
-
[31]
Zeilinger, and Sebastian Trimpe
Henrik Hose, Johannes K¨ ohler, Melanie N. Zeilinger, and Sebastian Trimpe. Approximate non-linear model predictive control with safety- augmented neural networks, October 2024
work page 2024
-
[32]
Roland Schwan, Colin N. Jones, and Daniel Kuhn. Stability Verification of Neural Network Controllers Using Mixed-Integer Programming. IEEE Transactions on Automatic Control, 68(12):7514–7529, December 2023
work page 2023
-
[33]
Stability and feasibility of neural network-based controllers via output range analysis
Benjamin Karg and Sergio Lucia. Stability and feasibility of neural network-based controllers via output range analysis. In 2020 59th IEEE Conference on Decision and Control (CDC), pages 4947–4954, December 2020
work page 2020
-
[34]
Safety Verification of Neural-Network-Based Controllers: A Set Invariance Approach
Louis Jouret, Adnane Saoud, and Sorin Olaru. Safety Verification of Neural-Network-Based Controllers: A Set Invariance Approach. IEEE Control Systems Letters, 7:3842–3847, 2023
work page 2023
-
[35]
Mahyar Fazlyab, Manfred Morari, and George J. Pappas. Safety Verifi- cation and Robustness Analysis of Neural Networks via Quadratic Con- straints and Semidefinite Programming. IEEE Transactions on Auto- matic Control, 67(1):1–15, January 2022
work page 2022
-
[36]
Daniela Lupu and Ion Necoara. Exact representation and efficient ap- 33 proximations of linear model predictive control laws via HardTanh type deep neural networks. Systems & Control Letters, 186:105742, April 2024
work page 2024
-
[37]
Alberto Bemporad, Manfred Morari, Vivek Dua, and Efstratios N. Pis- tikopoulos. The explicit linear quadratic regulator for constrained sys- tems. Automatica, 38(1):3–20, January 2002
work page 2002
-
[38]
Ganesh, Justin Katz, Nikolaos A
Iosif Pappas, Dustin Kenefake, Baris Burnak, Styliani Avraamidou, Hari S. Ganesh, Justin Katz, Nikolaos A. Diangelakis, and Efstratios N. Pistikopoulos. Multiparametric Programming in Process Systems Engi- neering: Recent Developments and Path Forward. Frontiers in Chemical Engineering, 2, January 2021
work page 2021
-
[39]
Exact representation of piecewise affine functions via neural networks
Moritz Schulze Darup. Exact representation of piecewise affine functions via neural networks. In 2020 European Control Conference (ECC), pages 1073–1078, May 2020
work page 2020
-
[40]
Vassilis Sakizlis, Konstantinos I. Kouramas, and Efstratios N. Pistikopou- los. Linear Model Predictive Control via Multiparametric Programming. In Multi-Parametric Model-Based Control , chapter 1, pages 1–23. John Wiley & Sons, Ltd, 2007
work page 2007
-
[41]
Efstratios N. Pistikopoulos, Nikolaos A. Diangelakis, and Richard Oberdieck. Multi-parametric/Explicit Model Predictive Control , chap- ter 10, pages 187–210. John Wiley & Sons, Ltd, 2020
work page 2020
-
[42]
Ppopt-multiparametric solver for explicit mpc
Dustin Kenefake and Efstratios N Pistikopoulos. Ppopt-multiparametric solver for explicit mpc. In Computer Aided Chemical Engineering , vol- ume 51, pages 1273–1278. Elsevier, 2022
work page 2022
-
[43]
Moustafa Ali, Xiaoqing Cai, Faisal I. Khan, Efstratios N. Pistikopou- los, and Yuhe Tian. Dynamic risk-based process design and operational optimization via multi-parametric programming. Digital Chemical Engi- neering, 7:100096, 2023
work page 2023
-
[44]
Modeling and predictive control of nonlinear processes using transfer learning method
Ming Xiao, Cheng Hu, and Zhe Wu. Modeling and predictive control of nonlinear processes using transfer learning method. AIChE Journal , 69(7):e18076, 2023
work page 2023
-
[45]
Diogo A. C. Narciso, Vivek Dua, and Efstratios N. Pistikopoulos. Mul- tiparametric Mixed-Integer Quadratic and Nonlinear Programming. In Multi-Parametric Programming, chapter 4, pages 73–97. John Wiley & Sons, Ltd, 2007. 34 A Corollary to Lemma 8 Corollary 23 Any affine equation with input x ∈ Rn can be exactly repre- sented by a single neuron if only the...
work page 2007
discussion (0)
Sign in with ORCID, Apple, or X to comment. Anyone can read and Pith papers without signing in.