publications

2023

1. ICML

   Social learning spontaneously emerges by searching optimal heuristics with deep reinforcement learning

   Seungwoong Ha, and Hawoong Jeong

   International Conference on Machine Learning (ICML) 2023, Poster, 2023

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   How have individuals of social animals in nature evolved to learn from each other, and what would be the optimal strategy for such learning in a specific environment? Here, we address both problems by employing a deep reinforcement learning model to optimize the social learning strategies (SLSs) of agents in a cooperative game in a multi-dimensional landscape. Throughout the training for maximizing the overall payoff, we find that the agent spontaneously learns various concepts of social learning, such as copying, focusing on frequent and well-performing neighbors, self-comparison, long-term cooperation between agents, and the importance of balancing between individual and social learning, without any explicit guidance or prior knowledge about the system. The SLS from a fully trained agent outperforms all of the traditional, baseline SLSs in terms of mean payoff. We demonstrate the superior performance of the reinforcement learning agent in various environments, including temporally changing environments and real social networks, which also verifies the adaptability of our framework to different social settings.

   @article{ha2022social,
     title = {Social learning spontaneously emerges by searching optimal heuristics with deep reinforcement learning},
     author = {Ha, Seungwoong and Jeong, Hawoong},
     journal = {International Conference on Machine Learning (ICML) 2023, Poster},
     year = {2023},
   }

2. ICLR

   Learning Heterogeneous Interaction Strengths by Trajectory Prediction with Graph Neural Network

   Seungwoong Ha, and Hawoong Jeong

   International Conference on Learning Representations (ICLR) 2023, Poster, 2023

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   Dynamical systems with interacting agents are universal in nature, commonly modeled by a graph of relationships between their constituents. Recently, various works have been presented to tackle the problem of inferring those relationships from the system trajectories via deep neural networks, but most of the studies assume binary or discrete types of interactions for simplicity. In the real world, the interaction kernels often involve continuous interaction strengths, which cannot be accurately approximated by discrete relations. In this work, we propose the relational attentive inference network (RAIN) to infer continuously weighted interaction graphs without any ground-truth interaction strengths. Our model employs a novel pairwise attention (PA) mechanism to refine the trajectory representations and a graph transformer to extract heterogeneous interaction weights for each pair of agents. We show that our RAIN model with the PA mechanism accurately infers continuous interaction strengths for simulated physical systems in an unsupervised manner. Further, RAIN with PA successfully predicts trajectories from motion capture data with an interpretable interaction graph, demonstrating the virtue of modeling unknown dynamics with continuous weights.

   @article{ha2022learning,
     title = {Learning Heterogeneous Interaction Strengths by Trajectory Prediction with Graph Neural Network},
     author = {Ha, Seungwoong and Jeong, Hawoong},
     journal = {International Conference on Learning Representations (ICLR) 2023, Poster},
     year = {2023},
   }

2021

1. PRR

   Discovering invariants via machine learning

   Seungwoong Ha, and Hawoong Jeong

   Physical Review Research, Dec 2021

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   Invariants and conservation laws convey critical information about the underlying dynamics of a system, yet it is generally infeasible to find them from large-scale data without any prior knowledge or human insight. We propose ConservNet to achieve this goal, a neural network that spontaneously discovers a conserved quantity from grouped data where the members of each group share invariants, similar to a general experimental setting where trajectories from different trials are observed. As a neural network trained with an intuitive loss function called noise-variance loss, ConservNet learns the hidden invariants in each group of multidimensional observables in a data-driven end-to-end manner. Our model successfully discovers underlying invariants from the simulated systems having invariants as well as a real-world double-pendulum trajectory. Since the model is robust to various noises and data conditions compared to the baseline, our approach is directly applicable to experimental data for discovering hidden conservation laws and further, general relationships between variables.

   @article{ha2021discovering,
     title = {Discovering invariants via machine learning},
     author = {Ha, Seungwoong and Jeong, Hawoong},
     journal = {Physical Review Research},
     volume = {3},
     number = {4},
     pages = {L042035},
     month = dec,
     year = {2021},
     publisher = {APS},
   }

2. Sci. Rep.

   Unraveling hidden interactions in complex systems with deep learning

   Seungwoong Ha, and Hawoong Jeong

   Scientific reports, Jun 2021

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   Rich phenomena from complex systems have long intrigued researchers, and yet modeling system micro-dynamics and inferring the forms of interaction remain challenging for conventional datadriven approaches, being generally established by scientists with human ingenuity. In this study, we propose AgentNet, a model-free data-driven framework consisting of deep neural networks to reveal and analyze the hidden interactions in complex systems from observed data alone. AgentNet utilizes a graph attention network with novel variable-wise attention to model the interaction between individual agents, and employs various encoders and decoders that can be selectively applied to any desired system. Our model successfully captured a wide variety of simulated complex systems, namely cellular automata (discrete), the Vicsek model (continuous), and active Ornstein–Uhlenbeck particles(non-Markovian) in which, notably, AgentNet’s visualized attention values coincided with the true variable-wise interaction strengths and exhibited collective behavior that was absent in the training data. A demonstration with empirical data from a fock of birds showed that AgentNet could identify hidden interaction ranges exhibited by real birds, which cannot be detected by conventional velocity correlation analysis. We expect our framework to open a novel path to investigating complex systems and to provide insight into general process-driven modeling.

   @article{ha2021unraveling,
     title = {Unraveling hidden interactions in complex systems with deep learning},
     author = {Ha, Seungwoong and Jeong, Hawoong},
     journal = {Scientific reports},
     volume = {11},
     number = {1},
     pages = {1--13},
     month = jun,
     year = {2021},
     publisher = {Springer},
   }

2016

1. Physica A

   Optimization strategy for and structural properties of traffic efficiency under bounded information accessibility

   Sanghyun Ahn, Seungwoong Ha, and Kim Soo Yong

   Physica A: Statistical Mechanics and its Applications, Jun 2016

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   A vital challenge for many socioeconomic systems is determining the optimum use of limited information. Traffic systems, wherein the range of resources is limited, are a particularly good example of this challenge. Based on bounded information accessibility in terms of, for example, high costs or technical limitations, we develop a new optimization strategy to improve the efficiency of a traffic system with signals and intersections. Numerous studies, including the study by Chowdery and Schadschneider (whose method we denote by ChSch), have attempted to achieve the maximum vehicle speed or the minimum wait time for a given traffic condition. In this paper, we introduce a modified version of ChSch with an independently functioning, decentralized control system. With the new model, we determine the optimization strategy under bounded information accessibility, which proves the existence of an optimal point for phase transitions in the system. The paper also provides insight that can be applied by traffic engineers to create more efficient traffic systems by analyzing the area and symmetry of local sites. We support our results with a statistical analysis using empirical traffic data from Seoul, Korea.

   @article{sanghyun2016optimization,
     title = {Optimization strategy for and structural properties of traffic efficiency under bounded information accessibility},
     author = {Ahn, Sanghyun and Ha, Seungwoong and Soo Yong, Kim},
     journal = {Physica A: Statistical Mechanics and its Applications},
     volume = {451},
     pages = {578--591},
     month = jun,
     year = {2016},
     publisher = {Elsevier},
     url = {http://link.aps.org/doi/10.1103/PhysRev.47.777},
   }