arXiv subjects

Suzhou Huang

Publications and source records attributed to Suzhou Huang.

16 recordsLinked to original sources

arXiv2025

Coordinated Car-following Using Distributed MPC

Within the modeling framework of Markov games, we propose a series of algorithms for coordinated car-following using distributed model predictive control (DMPC). Instead of tracking prescribed feasible trajectories, driving policies are solved directly as outcomes of the DMPC optimization given the driver's perceivable states. The coordinated solutions are derived using the best response dynamics via iterated self-play, and are facilitated by direct negotiation using inter-agent or agent-infrastructure communication. These solutions closely approximate either Nash equilibrium or centralized optimization. By re-parameterizing the action sequence in DMPC as a curve along the planning horizon, we are able to systematically reduce the original DMPC to very efficient grid searches such that the optimal solution to the original DMPC can be well executed in real-time. Within our modeling framework, it is natural to cast traffic control problems as mechanism design problems, in which all agents are endogenized on an equal footing with full incentive compatibility. We show how traffic efficiency can be dramatically improved while keeping stop-and-go phantom waves tamed at high vehicle densities. Our approach can be viewed as an alternative way to formulate coordinated adaptive cruise control (CACC) without an explicit platooning (or with all vehicles in the traffic system treated as a single extended platoon). We also address the issue of linear stability of the associated discrete-time traffic dynamics and demonstrate why it does not always tell the full story about the traffic stability.

eess.SY↗

arXiv2025

Taming Spontaneous Stop-and-Go Traffic Waves: A Computational Mechanism Design Perspective

It is well known that stop-and-go waves can be generated spontaneously in traffic even without bottlenecks. Can such undesirable traffic patterns, induced by intrinsic human driving behaviors, be tamed effectively and inexpensively? Taking advantage of emerging connectivity and autonomy technologies, we envision a simple yet realistic traffic control system to achieve this goal. To prove the concept, we design such a system to suppress these waves while maximizing traffic throughput in the Tadaki setting: a circular road with varying number of vehicles. We first introduce our driver behavior model and demonstrate how our calibrated human driving agents can closely reproduce the observed human driving patterns in the original Tadaki experiment. We then propose a simple control system mediated via connected automated vehicles (CAV) whose ideal speed parameter is treated as a system-level control variable adapted to the local vehicle density of the traffic. The objective of the control system is set up as a tradeoff: maximizing throughput while minimizing traffic oscillation. Following computational mechanism design, we search for the optimal control policy as a function of vehicle density and the tradeoff attitude parameter. This can be done by letting all vehicles play a simulated game of CAV-modulated traffic under such a control system. Our simulation results show that the improvements in traffic efficiency and smoothness are substantial. Finally, we envision how such a traffic control system can be realized in an environment with smart vehicles connected to a smart infrastructure or via a scheme of variable speed advisory.

eess.SY↗

arXiv2025

Taming Spontaneous Stop-and-Go Traffic Waves: A Bifurcation Perspective of A Dynamical Map

We consider a discrete-time dynamical system in a car-following context. The system was recently introduced to parsimoniously model human driving behavior based on utility maximization. The parameters of the model were calibrated using vehicle trajectory data from the Sugiyama experiment. It was shown that such a system can accurately reproduce the observed collective phenomena of a more elaborate experiment by Tadaki et al. Once the heterogeneity and noise are switched off, the model defines a map of the corresponding discrete-time dynamical system. We first perform a bifurcation analysis of the map by studying the stability of its limit solutions: a free-flow fixed point and a stop-and-go quasi-periodic orbit. When the vehicle density is varied, our model displays a bifurcation diagram qualitatively similar to those found in a class of optimal velocity models based on an ordinary differential equation approach, including regimes where one or both of the limit solutions are stable. In a 2D bifurcation diagram we further demonstrate that imposing a vehicle density-dependent speed advisory can dissipate the stop-and-go quasi-periodic orbit. This in turn lays the mathematical foundation for a simple, yet effective proposal [1] to tame stop-and-go waves, improving traffic flow and smoothness simultaneously via variable speed advisory.

eess.SY↗

arXiv2023

Potential Game-Based Decision-Making for Autonomous Driving

Decision-making for autonomous driving is challenging, considering the complex interactions among multiple traffic agents (e.g., autonomous vehicles (AVs), human drivers, and pedestrians) and the computational load needed to evaluate these interactions. This paper develops two general potential game based frameworks, namely, finite and continuous potential games, for decision-making in autonomous driving. The two frameworks account for the AVs' two types of action spaces, i.e., finite and continuous action spaces, respectively. We show that the developed frameworks provide theoretical guarantees, including 1) existence of pure-strategy Nash equilibria, 2) convergence of the Nash equilibrium (NE) seeking algorithms, and 3) global optimality of the derived NE (in the sense that both self- and team- interests are optimized). In addition, we provide cost function shaping approaches to constructing multi-agent potential games in autonomous driving. Moreover, two solution algorithms, including self-play dynamics (e.g., best response dynamics) and potential function optimization, are developed for each game. The developed frameworks are then applied to two different traffic scenarios, including intersection-crossing and lane-changing in highways. Statistical comparative studies, including 1) finite potential game vs. continuous potential game, and 2) best response dynamics vs. potential function optimization, are conducted to compare the performances of different solution algorithms. It is shown that both developed frameworks are practical (i.e., computationally efficient), reliable (i.e., resulting in satisfying driving performances in diverse scenarios and situations), and robust (i.e., resulting in satisfying driving performances against uncertain behaviors of the surrounding vehicles) for real-time decision-making in autonomous driving.

eess.SY↗

arXiv2021

Calibration of Human Driving Behavior and Preference Using Naturalistic Traffic Data

Understanding human driving behaviors quantitatively is critical even in the era when connected and autonomous vehicles and smart infrastructure are becoming ever more prevalent. This is particularly so as that mixed traffic settings, where autonomous vehicles and human driven vehicles co-exist, are expected to persist for quite some time. Towards this end it is necessary that we have a comprehensive modeling framework for decision-making within which human driving preferences can be inferred statistically from observed driving behaviors in realistic and naturalistic traffic settings. Leveraging a recently proposed computational framework for smart vehicles in a smart world using multi-agent based simulation and optimization, we first recapitulate how the forward problem of driving decision-making is modeled as a state space model. We then show how the model can be inverted to estimate driver preferences from naturalistic traffic data using the standard Kalman filter technique. We explicitly illustrate our approach using the vehicle trajectory data from Sugiyama experiment that was originally meant to demonstrate how stop-and-go shockwave can arise spontaneously without bottlenecks. Not only the estimated state filter can fit the observed data well for each individual vehicle, the inferred utility functions can also re-produce quantitatively similar pattern of the observed collective behaviors. One distinct advantage of our approach is the drastically reduced computational burden. This is possible because our forward model treats driving decision process, which is intrinsically dynamic with multi-agent interactions, as a sequence of independent static optimization problems contingent on the state with a finite look ahead anticipation. Consequently we can practically sidestep solving an interacting dynamic inversion problem that would have been much more computationally demanding.

cs.MA↗

arXiv2020

Towards a Systematic Computational Framework for Modeling Multi-Agent Decision-Making at Micro Level for Smart Vehicles in a Smart World

We propose a multi-agent based computational framework for modeling decision-making and strategic interaction at micro level for smart vehicles in a smart world. The concepts of Markov game and best response dynamics are heavily leveraged. Our aim is to make the framework conceptually sound and computationally practical for a range of realistic applications, including micro path planning for autonomous vehicles. To this end, we first convert the would-be stochastic game problem into a closely related deterministic one by introducing risk premium in the utility function for each individual agent. We show how the sub-game perfect Nash equilibrium of the simplified deterministic game can be solved by an algorithm based on best response dynamics. In order to better model human driving behaviors with bounded rationality, we seek to further simplify the solution concept by replacing the Nash equilibrium condition with a heuristic and adaptive optimization with finite look-ahead anticipation. In addition, the algorithm corresponding to the new solution concept drastically improves the computational efficiency. To demonstrate how our approach can be applied to realistic traffic settings, we conduct a simulation experiment: to derive merging and yielding behaviors on a double-lane highway with an unexpected barrier. Despite assumption differences involved in the two solution concepts, the derived numerical solutions show that the endogenized driving behaviors are very similar. We also briefly comment on how the proposed framework can be further extended in a number of directions in our forthcoming work, such as behavioral calibration using real traffic video data, computational mechanism design for traffic policy optimization, and so on.

cs.MA↗

arXiv2020

A Game Theoretic Approach for Parking Spot Search with Limited Parking Lot Information

We propose a game theoretic approach to address the problem of searching for available parking spots in a parking lot and picking the ``optimal'' one to park. The approach exploits limited information provided by the parking lot, i.e., its layout and the current number of cars in it. Considering the fact that such information is or can be easily made available for many structured parking lots, the proposed approach can be applicable without requiring major updates to existing parking facilities. For large parking lots, a sampling-based strategy is integrated with the proposed approach to overcome the associated computational challenge. The proposed approach is compared against a state-of-the-art heuristic-based parking spot search strategy in the literature through simulation studies and demonstrates its advantage in terms of achieving lower cost function values.

cs.RO↗

arXiv1996

The Dimensionally Reduced Effective Theory for Quarks in High Temperature QCD

We show that QCD undergoes dimensional reduction at high temperatures also in the quark sector. In the kinematic region relevant to screening physics, where the lowest Matsubara modes are close to their ``mass-shells'', all static Green's functions involving both quarks and gluons, are reproducible in the high-$T$ limit by a renormalizable three dimensional Lagrangian up to order $\tilde{g}^2(T)\sim 1/ln T$. This three dimensional theory only contains explicitly the lightest bosonic and fermionic Matsubara modes, while the heavier modes correct the tree-level couplings and generate extra local vertices. We also find that the quark degrees of freedom that have been retained in the reduced theory are nonrelativistic in the high-$T$ limit. We then improve our result to order $\tilde{g}^4(T)$ through an explicit nonrelativistic expansion, in the spirit of the heavy quark effective theory. This effective theory is relevant for studying QCD screening phenomena with observables made from quarks, e.g. mesonic and baryonic currents, already at temperatures not much higher than the chiral transition temperature $T_c$.

hep-ph↗

arXiv1996

When Is A Semiclassical Approximation Self-consistent?

A general condition for the self-consistency of a semiclassical approximation to a given system is suggested. It is based on the eigenvalue distribution of the relevant Hessian evaluated at the streamline configurations (configurations that almost satisfy the classical equations of motion). The semiclassical approximation is consistent when there exists a gap that separates small and large eigenvalues and the spreading among the small eigenvalues is much smaller than the gap. The idea is illustrated in the case of the double-well potential problem in quantum mechanics. The feasibility of the present idea to test instanton models of QCD vacuum is also briefly discussed.

hep-ph↗

arXiv1996

Contrasting Real-time Dynamics with Screening Phenomena at Finite Temperature

We discuss the interpretation of Euclidean correlation functions at finite temperature ($T$) and their relationship with the corresponding real-time Green's functions. The soluble 2+1 dimensional Gross-Neveu model in the large-$N$ limit is used throughout as a working example. First, the real-time bound state, identified as an elementary excitation at finite $T$, is solved. The bound state mass, the dispersion relation at low momenta, the coupling constant and decay constant are calculated. To characterize the structure of the bound state the on-shell form factor is carefully introduced and calculated. Then we examine the corresponding screening state and contrast the screening mass, coupling constant, decay constant and the screening Bethe-Salpeter amplitude with the real-time quantities. We find that, although they can be used as qualitative indicators in the low-$T$ regime, the screening states at finite $T$ in general do not reflect the properties of the corresponding real-time bound states. Besides, other relevant issues, such as the subtlety of the real-time manifestation of conservation laws due to some internal symmetries at $T\ne 0$, the temperature dependence of the pseudoscalar spectral function and its sum rule, and the high-$T$ limit of the screening state and its implications to the dimensional reduction, are also discussed in detail.

hep-ph↗

arXiv1995

$Z_3$ Twisted Chiral Condensates in QCD at Finite Temperatures

It was recently observed in a lattice QCD measurement that the chiral condensate in the quenched approximation shows dramatically different behavior in the three $Z_3$-equivalent de-confined phases. We argue that this phenomenon can be understood qualitatively as an effect of $Z_3$ twists on fermionic fields. Quarks under these $Z_3$-twists become global anyons and hence display different thermodynamic properties. We further show that the lattice data can be roughly modeled by a Nambu-Jona-Lasinio type Lagrangian with a minimal coupling to a constant gauge field $A_0=2πnT/3$ (with $n=0$, $\pm1$), which arises naturally from the non-trivial phase of the Polyakov line.

hep-ph↗

arXiv1995

DIMENSIONAL REDUCTION AT HIGH TEMPERATURE FOR FERMIONS

The concept of dimensional reduction in the high temperature regime is generalized to static Green's functions of composite operators that contain fermionic fields. The recognition of a natural kinematic region where the lowest Matsubara modes are close to their mass-shell, and the ultraviolet behavior of the running coupling constant of the original theory are crucial for providing the necessary scale hierarchy. The general strategy is illustrated in the asymptotically-free Gross-Neveu model in 1+1 dimensions, where we verify that dimensional reduction occurs to the leading order in $g^2(T)$. We also find, in the same model, that the scale parameter characterizing the dependence on temperature of the coupling constant in the reduced theory, $Λ_T$, is considerably smaller than $Λ_{\bar{\text{MS}}}$. Implications of our results for QCD are also discussed.

hep-ph↗

arXiv1994

The Relevant Scale Parameter in the High Temperature Phase of QCD

We introduce the running coupling constant of QCD in the high temperature phase, $\tilde{g}^2(T)$, through a renormalization scheme where the dimensional reduction is optimal at the one-loop level. We then calculate the relevant scale parameter, $Λ_T$, which characterizes the running of $\tilde{g}^2(T)$ with $T$, using the background field method in the static sector. It is found that $Λ_T/Λ_{\overline{\text{MS}}} =e^{(γ_E+1/22)}/(4π)\approx 0.148$. We further verify that the coupling $\tilde{g}^2(T)$ is also optimal for lattice perturbative calculations. Our result naturally explains why the high temperature limit of QCD sets in at temperatures as low as a few times the critical temperature. In addition, our $Λ_T$ agrees remarkably well with the scale parameter determined from the lattice measurement of the spatial string tension of the SU(2) gauge theory at high $T$.

hep-ph↗

arXiv1994

Statistical Mechanics of Relativistic Aynon-like Systems

To study the manifestation of the Aharonov-Bohm effect in many-body systems we consider the statistical mechanics of the Gross-Neveu model on a ring (1+1 dimensions) and on a cylinder (2+1 dimensions) with a thin solenoid coinciding with the axis. For such systems with a non-trivial magnetic flux ($θ$) many thermodynamical observables, such as the order parameter, induced current and virial coefficients, display periodic but non-analytic dependence on $θ$. In the 2+1 dimensional case we further find that there is an interval of $θ\in(1/3,2/3)$ (modulo integers) where parity is always spontaneously broken, independent of the circumference of the cylinder. We show that the mean-field character of the phase transitions is preserved to the leading order in $1/N$, by verifying the $θ$-independence of all the critical exponents. The precise nature of the quasi-particle, locally fermion-like and globally anyon-like, is illuminated through the calculation of the equal-time commutator and the decomposition of the propagator into a sum over paths classified by winding numbers.

cond-mat↗

arXiv1993

A Non-Abelian Variation on the Savvidy Vacuum of the Yang-Mills Gauge Theory

As a prelude to a truly non-perturbative evaluation of the effective potential in terms of lattice QCD, the one loop effective potential for a non-Abelian gauge configuration is calculated using the background field method. Through a non-trivial correlation between the space and color orientations the new background field avoids the possible coordinate singularity, ${\rm Det}B_i^a=0$, observed recently by Ken Johnson and his collaborators in their Schrödinger functional study of the SU(2) Yang-Mills theory. In addition, since our ansatz generates a constant color magnetic field through the commutator terms rather than derivative terms, many of the technical drawbacks the Savvidy ansatz suffers on a lattice can be avoided. Our one loop study yields qualitatively the same result as that of Savvidy's.

hep-lat↗

arXiv1993

Nucleon Solution of the Faddeev Equation in the Nambu-Jona-Lasinio Model

Given the phenomenological success of the Nambu-Jona-Lasinio model in describing the meson physics in the low energy limit, it is tempting to find the fully relativistically structured nucleon solution in the same model under the similar approximation employed in the mesonic sector. To achieve this goal we need to solve a relativistic Faddeev equation. The factorizability of the two-body T-matrix reduces the three-body Faddeev equation to a tractable two-body Bethe-Salpeter equation. The reduced equation is then solved numerically. Our result indicates that the nucleon consists of three loosely bound constituent quarks.

hep-ph↗