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Bohan Wang

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20 papers

2 author rows

EAAI Journal 2026 Journal Article

A twin-branch decoupled network for multi-class unsupervised anomaly detection

Bohan Wang
Jihong Wan
Jie Zhao
Xiaocao Ouyang
Xiaoping Li

The use of powerful pre-trained Vision Transformer (ViT) encoders in Multi-Class Unsupervised Anomaly Detection (MUAD) can lead to an “identity mapping shortcut”, where the model’s strong generalization inadvertently reconstructs anomalies. To address this specific manifestation of the over-generalization problem, this paper proposes DAD-Net, an innovative hybrid framework combining ViT and Convolutional Neural Networks (CNNs) that imposes synergistic constraints from both the model architecture and the training objective. Architecturally, a novel asymmetric twin-branch CNN decoder is designed to achieve a multi-scale reconstruction of normal patterns. Its shallow branch is specialized for reconstructing high-frequency textures, while its deep branch models abstract semantics. At the objective level, a hard feature loss compels the model to focus on the most complex normal patterns, effectively inhibiting the formation of the “identity mapping shortcut”. Comprehensive experiments validate DAD-Net’s direct applicability to engineering tasks. For industrial defect detection, the framework achieves superior performance on standard benchmarks. Furthermore, the model shows excellent generalization on a challenging cross-domain medical dataset. This highlights its potential as a versatile tool for other critical domains, such as medical diagnostic support. Ablation studies confirm the effectiveness of our core designs, positioning DAD-Net as a robust and practical solution for real-world quality control systems.

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NeurIPS Conference 2025 Conference Paper

CAGE: Continuity-Aware edGE Network Unlocks Robust Floorplan Reconstruction

Yiyi Liu
Chunyang Liu
Bohan Wang
Weiqin Jiao
Bojian Wu
Lubin Fan
Yuwei Chen
Fashuai Li

We present CAGE (Continuity-Aware edGE) network, a robust framework for reconstructing vector floorplans directly from point-cloud density maps. Traditional corner-based polygon representations are highly sensitive to noise and incomplete observations, often resulting in fragmented or implausible layouts. Recent line grouping methods leverage structural cues to improve robustness but still struggle to recover fine geometric details. To address these limitations, we propose a native edge-centric formulation, modeling each wall segment as a directed, geometrically continuous edge. This representation enables inference of coherent floorplan structures, ensuring watertight, topologically valid room boundaries while improving robustness and reducing artifacts. Towards this design, we develop a dual-query transformer decoder that integrates perturbed and latent queries within a denoising framework, which not only stabilizes optimization but also accelerates convergence. Extensive experiments on Structured3D and SceneCAD show that CAGE achieves state-of-the-art performance, with F1 scores of 99. 1% (rooms), 91. 7% (corners), and 89. 3% (angles). The method also demonstrates strong cross-dataset generalization, underscoring the efficacy of our architectural innovations. Code and pretrained models are available on our project page: https: //github. com/ee-Liu/CAGE. git.

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NeurIPS Conference 2025 Conference Paper

Continuous-time Riemannian SGD and SVRG Flows on Wasserstein Probabilistic Space

Mingyang Yi
Bohan Wang

Recently, optimization on the Riemannian manifold have provided valuable insights to the optimization community. In this regard, extending these methods to to the Wasserstein space is of particular interest, since optimization on Wasserstein space is closely connected to practical sampling processes. Generally, the standard (continuous) optimization method on Wasserstein space is Riemannian gradient flow (i. e. , Langevin dynamics when minimizing KL divergence). In this paper, we aim to enrich the family of continuous optimization methods in the Wasserstein space, by extending the gradient flow on it into the stochastic gradient descent (SGD) flow and stochastic variance reduction gradient (SVRG) flow. By leveraging the property of Wasserstein space, we construct stochastic differential equations (SDEs) to approximate the corresponding discrete Euclidean dynamics of the desired Riemannian stochastic methods. Then, we obtain the flows in Wasserstein space by Fokker-Planck equation. Finally, we establish convergence rates of the proposed stochastic flows, which align with those known in the Euclidean setting.

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NeurIPS Conference 2025 Conference Paper

RobotSmith: Generative Robotic Tool Design for Acquisition of Complex Manipulation Skills

Chunru Lin
Haotian Yuan
Yian Wang
Xiaowen Qiu
Tsun-Hsuan Johnson Wang
Minghao Guo
Bohan Wang
Yashraj Narang

Endowing robots with tool design abilities is critical for enabling them to solve complex manipulation tasks that would otherwise be intractable. While recent generative frameworks can automatically synthesize task settings—such as 3D scenes and reward functions—they have not yet addressed the challenge of tool-use scenarios. Simply retrieving human-designed tools might not be ideal since many tools (e. g. , a rolling pin) are difficult for robotic manipulators to handle. Furthermore, existing tool design approaches either rely on predefined templates with limited parameter tuning or apply generic 3D generation methods that are not optimized for tool creation. To address these limitations, we propose RobotSmith, an automated pipeline that leverages the implicit physical knowledge embedded in vision-language models (VLMs) alongside the more accurate physics provided by physics simulations to design and use tools for robotic manipulation. Our system (1) iteratively proposes tool designs using collaborative VLM agents, (2) generates low-level robot trajectories for tool use, and (3) jointly optimizes tool geometry and usage for task performance. We evaluate our approach across a wide range of manipulation tasks involving rigid, deformable, and fluid objects. Experiments show that our method consistently outperforms strong baselines in both task success rate and overall performance. Notably, our approach achieves a 50. 0\% average success rate, significantly surpassing other baselines such as 3D generation (21. 4\%) and tool retrieval (11. 1\%). Finally, we deploy our system in real-world settings, demonstrating that the generated tools and their usage plans transfer effectively to physical execution, validating the practicality and generalization capabilities of our approach.

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NeurIPS Conference 2025 Conference Paper

Selftok-Zero: Reinforcement Learning for Visual Generation via Discrete and Autoregressive Visual Tokens

Bohan Wang
Mingze Zhou
Zhongqi Yue
Wang Lin
Kaihang Pan
Liyu Jia
Wentao Hu
Wei Zhao

Reinforcement learning (RL) has become an indispensable post-training step for unlocking the full potential of Large Language Models (LLMs). Its core motivation is to incentivize the model’s inference trajectory via a reward model, effectively balancing the exploration–exploitation trade-off in scenarios where collecting exhaustive input–output ground-truth pairs is infeasible. This motivation naturally extends to visual generation, where perfect alignment between an image and a textual prompt is inherently ambiguous and often unattainable. However, existing visual generative models are not yet ready for RL due to the following two fundamental drawbacks that undermine the foundations of RL: 1) For diffusion-based models, the actual generation trajectories of sampled images cannot be reliably rewarded, as diffusion inversion is notoriously difficult. 2) For autoregressive (AR) models, we show that the widely used spatial visual tokens do not satisfy the Bellman equation and thus violate the policy improvement theorem of RL. To this end, we propose to use Selftok (Self-consistency Tokenizer), which represents each image as a sequential 1D stream of discrete, autoregressive tokens. Together with language, we train a pure AR vision-language model (VLM) for visual generation. Impressively, without using any text-image training pairs, a simple policy gradient algorithm applied to Selftok tokens significantly boosts visual generation performance, surpassing existing models by a large margin. Implementation details are provided in the Appendix.

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ICLR Conference 2025 Conference Paper

TetSphere Splatting: Representing High-Quality Geometry with Lagrangian Volumetric Meshes

Minghao Guo
Bohan Wang
Kaiming He
Wojciech Matusik

We introduce TetSphere Splatting, a Lagrangian geometry representation designed for high-quality 3D shape modeling. TetSphere splatting leverages an underused yet powerful geometric primitive -- volumetric tetrahedral meshes. It represents 3D shapes by deforming a collection of tetrahedral spheres, with geometric regularizations and constraints that effectively resolve common mesh issues such as irregular triangles, non-manifoldness, and floating artifacts. Experimental results on multi-view and single-view reconstruction highlight TetSphere splatting's superior mesh quality while maintaining competitive reconstruction accuracy compared to state-of-the-art methods. Additionally, TetSphere splatting demonstrates versatility by seamlessly integrating into generative modeling tasks, such as image-to-3D and text-to-3D generation.

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NeurIPS Conference 2024 Conference Paper

Physically Compatible 3D Object Modeling from a Single Image

Minghao Guo
Bohan Wang
Pingchuan Ma
Tianyuan Zhang
Crystal E. Owens
Chuang Gan
Joshua B. Tenenbaum
Kaiming He

We present a computational framework that transforms single images into 3D physical objects. The visual geometry of a physical object in an image is determined by three orthogonal attributes: mechanical properties, external forces, and rest-shape geometry. Existing single-view 3D reconstruction methods often overlook this underlying composition, presuming rigidity or neglecting external forces. Consequently, the reconstructed objects fail to withstand real-world physical forces, resulting in instability or undesirable deformation -- diverging from their intended designs as depicted in the image. Our optimization framework addresses this by embedding physical compatibility into the reconstruction process. We explicitly decompose the three physical attributes and link them through static equilibrium, which serves as a hard constraint, ensuring that the optimized physical shapes exhibit desired physical behaviors. Evaluations on a dataset collected from Objaverse demonstrate that our framework consistently enhances the physical realism of 3D models over existing methods. The utility of our framework extends to practical applications in dynamic simulations and 3D printing, where adherence to physical compatibility is paramount.

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NeurIPS Conference 2023 Conference Paper

Closing the gap between the upper bound and lower bound of Adam's iteration complexity

Bohan Wang
Jingwen Fu
Huishuai Zhang
Nanning Zheng
Wei Chen

Recently, Arjevani et al. [1] establish a lower bound of iteration complexity for the first-order optimization under an $L$-smooth condition and a bounded noise variance assumption. However, a thorough review of existing literature on Adam's convergence reveals a noticeable gap: none of them meet the above lower bound. In this paper, we close the gap by deriving a new convergence guarantee of Adam, with only an $L$-smooth condition and a bounded noise variance assumption. Our results remain valid across a broad spectrum of hyperparameters. Especially with properly chosen hyperparameters, we derive an upper bound of the iteration complexity of Adam and show that it meets the lower bound for first-order optimizers. To the best of our knowledge, this is the first to establish such a tight upper bound for Adam's convergence. Our proof utilizes novel techniques to handle the entanglement between momentum and adaptive learning rate and to convert the first-order term in the Descent Lemma to the gradient norm, which may be of independent interest.

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ICLR Conference 2023 Conference Paper

DiGress: Discrete Denoising diffusion for graph generation

Clément Vignac
Igor Krawczuk
Antoine Siraudin
Bohan Wang
Volkan Cevher
Pascal Frossard

This work introduces DiGress, a discrete denoising diffusion model for generating graphs with categorical node and edge attributes. Our model utilizes a discrete diffusion process that progressively edits graphs with noise, through the process of adding or removing edges and changing the categories. A graph transformer network is trained to revert this process, simplifying the problem of distribution learning over graphs into a sequence of node and edge classification tasks. We further improve sample quality by introducing a Markovian noise model that preserves the marginal distribution of node and edge types during diffusion, and by incorporating auxiliary graph-theoretic features. A procedure for conditioning the generation on graph-level features is also proposed. DiGress achieves state-of-the-art performance on molecular and non-molecular datasets, with up to 3x validity improvement on a planar graph dataset. It is also the first model to scale to the large GuacaMol dataset containing 1.3M drug-like molecules without the use of molecule-specific representations.

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NeurIPS Conference 2023 Conference Paper

Fast Conditional Mixing of MCMC Algorithms for Non-log-concave Distributions

Xiang Cheng
Bohan Wang
Jingzhao Zhang
Yusong Zhu

MCMC algorithms offer empirically efficient tools for sampling from a target distribution $\pi(x) \propto \exp(-V(x))$. However, on the theory side, MCMC algorithms suffer from slow mixing rate when $\pi(x)$ is non-log-concave. Our work examines this gap and shows that when Poincar\'e-style inequality holds on a subset $\mathcal{X}$ of the state space, the conditional distribution of MCMC iterates over $\mathcal{X}$ mixes fast to the true conditional distribution. This fast mixing guarantee can hold in cases when global mixing is provably slow. We formalize the statement and quantify the conditional mixing rate. We further show that conditional mixing can have interesting implications for sampling from mixtures of Gaussians, parameter estimation for Gaussian mixture models, and Gibbs-sampling with well-connected local minima.

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NeurIPS Conference 2023 Conference Paper

On the Trade-off of Intra-/Inter-class Diversity for Supervised Pre-training

Jieyu Zhang
Bohan Wang
Zhengyu Hu
Pang Wei W. Koh
Alexander J. Ratner

Pre-training datasets are critical for building state-of-the-art machine learning models, motivating rigorous study on their impact on downstream tasks. In this work, we study the impact of the trade-off between the intra-class diversity (the number of samples per class) and the inter-class diversity (the number of classes) of a supervised pre-training dataset. Empirically, we found that with the size of the pre-training dataset fixed, the best downstream performance comes with a balance on the intra-/inter-class diversity. To understand the underlying mechanism, we show theoretically that the downstream performance depends monotonically on both types of diversity. Notably, our theory reveals that the optimal class-to-sample ratio (#classes / #samples per class) is invariant to the size of the pre-training dataset, which motivates an application of predicting the optimal number of pre-training classes. We demonstrate the effectiveness of this application by an improvement of around 2 points on the downstream tasks when using ImageNet as the pre-training dataset.

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ICLR Conference 2023 Conference Paper

𝒪-GNN: incorporating ring priors into molecular modeling

Jinhua Zhu 0001
Kehan Wu
Bohan Wang
Yingce Xia
Shufang Xie 0003
Qi Meng
Lijun Wu 0003
Tao Qin 0001

Cyclic compounds that contain at least one ring play an important role in drug design. Despite the recent success of molecular modeling with graph neural networks (GNNs), few models explicitly take rings in compounds into consideration, consequently limiting the expressiveness of the models. In this work, we design a new variant of GNN, ring-enhanced GNN ($\mathcal{O}$-GNN), that explicitly models rings in addition to atoms and bonds in compounds. In $\mathcal{O}$-GNN, each ring is represented by a latent vector, which contributes to and is iteratively updated by atom and bond representations. Theoretical analysis shows that $\mathcal{O}$-GNN is able to distinguish two isomorphic subgraphs lying on different rings using only one layer while conventional graph convolutional neural networks require multiple layers to distinguish, demonstrating that $\mathcal{O}$-GNN is more expressive. Through experiments, $\mathcal{O}$-GNN shows good performance on $\bf{11}$ public datasets. In particular, it achieves state-of-the-art validation result on the PCQM4Mv1 benchmark (outperforming the previous KDDCup champion solution) and the drug-drug interaction prediction task on DrugBank. Furthermore, $\mathcal{O}$-GNN outperforms strong baselines (without modeling rings) on the molecular property prediction and retrosynthesis prediction tasks.

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ICLR Conference 2022 Conference Paper

Creating Training Sets via Weak Indirect Supervision

Jieyu Zhang 0001
Bohan Wang
Xiangchen Song
Yujing Wang 0005
Yaming Yang 0001
Jing Bai 0010
Alexander Ratner

Creating labeled training sets has become one of the major roadblocks in machine learning. To address this, recent Weak Supervision (WS) frameworks synthesize training labels from multiple potentially noisy supervision sources. However, existing frameworks are restricted to supervision sources that share the same output space as the target task. To extend the scope of usable sources, we formulate Weak Indirect Supervision (WIS), a new research problem for automatically synthesizing training labels based on indirect supervision sources that have different output label spaces. To overcome the challenge of mismatched output spaces, we develop a probabilistic modeling approach, PLRM, which uses user-provided label relations to model and leverage indirect supervision sources. Moreover, we provide a theoretically-principled test of the distinguishability of PLRM for unseen labels, along with an generalization bound. On both image and text classification tasks as well as an industrial advertising application, we demonstrate the advantages of PLRM by outperforming baselines by a margin of 2%-9%.

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NeurIPS Conference 2022 Conference Paper

Does Momentum Change the Implicit Regularization on Separable Data?

Bohan Wang
Qi Meng
Huishuai Zhang
Ruoyu Sun
Wei Chen
Zhi-Ming Ma
Tie-Yan Liu

The momentum acceleration technique is widely adopted in many optimization algorithms. However, there is no theoretical answer on how the momentum affects the generalization performance of the optimization algorithms. This paper studies this problem by analyzing the implicit regularization of momentum-based optimization. We prove that on the linear classification problem with separable data and exponential-tailed loss, gradient descent with momentum (GDM) converges to the $L^2$ max-margin solution, which is the same as vanilla gradient descent. That means gradient descent with momentum acceleration still converges to a low-complexity model, which guarantees their generalization. We then analyze the stochastic and adaptive variants of GDM (i. e. , SGDM and deterministic Adam) and show they also converge to the $L^2$ max-margin solution. Technically, the implicit regularization of SGDM is established based on a novel convergence analysis of SGDM under a general noise condition called affine noise variance condition. To the best of our knowledge, we are the first to derive SGDM’s convergence under such an assumption. Numerical experiments are conducted to support our theoretical results.

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ICRA Conference 2021 Conference Paper

A Simulation-Based Grasp Planner for Enabling Robotic Grasping during Composite Sheet Layup

Omey M. Manyar
Jaineel Desai
Nimish Deogaonkar
Rex Jomy Joseph
Rishi K. Malhan
Zachary McNulty
Bohan Wang
Jernej Barbic

Composites are increasingly becoming a material of choice in the aerospace and automotive industries. Currently, many composite parts are produced by manually laying up sheets on complex molds. Composite sheet layup requires executing two main tasks: (1) grasping a sheet and (2) draping it on the mold. Automating the layup process requires automation of these two tasks. This paper is focused on the automation of the grasping task using robots. This requires an automated generation of grasp plans to enable robots to hold the sheet during the draping process. We present a simulation-based approach for determining robot grasp locations on the composite sheets. We also present an intervention controller that uses a real-time sheet tracking system during plan execution and can prevent failures. We demonstrate the performance of the developed system using a large complex part.

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NeurIPS Conference 2021 Conference Paper

Optimizing Information-theoretical Generalization Bound via Anisotropic Noise of SGLD

Bohan Wang
Huishuai Zhang
Jieyu Zhang
Qi Meng
Wei Chen
Tie-Yan Liu

Recently, the information-theoretical framework has been proven to be able to obtain non-vacuous generalization bounds for large models trained by Stochastic Gradient Langevin Dynamics (SGLD) with isotropic noise. In this paper, we optimize the information-theoretical generalization bound by manipulating the noise structure in SGLD. We prove that with constraint to guarantee low empirical risk, the optimal noise covariance is the square root of the expected gradient covariance if both the prior and the posterior are jointly optimized. This validates that the optimal noise is quite close to the empirical gradient covariance. Technically, we develop a new information-theoretical bound that enables such an optimization analysis. We then apply matrix analysis to derive the form of optimal noise covariance. Presented constraint and results are validated by the empirical observations.

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NeurIPS Conference 2021 Conference Paper

See More for Scene: Pairwise Consistency Learning for Scene Classification

Gongwei Chen
Xinhang Song
Bohan Wang
Shuqiang Jiang

Scene classification is a valuable classification subtask and has its own characteristics which still needs more in-depth studies. Basically, scene characteristics are distributed over the whole image, which cause the need of “seeing” comprehensive and informative regions. Previous works mainly focus on region discovery and aggregation, while rarely involves the inherent properties of CNN along with its potential ability to satisfy the requirements of scene classification. In this paper, we propose to understand scene images and the scene classification CNN models in terms of the focus area. From this new perspective, we find that large focus area is preferred in scene classification CNN models as a consequence of learning scene characteristics. Meanwhile, the analysis about existing training schemes helps us to understand the effects of focus area, and also raises the question about optimal training method for scene classification. Pursuing the better usage of scene characteristics, we propose a new learning scheme with a tailored loss in the goal of activating larger focus area on scene images. Since the supervision of the target regions to be enlarged is usually lacked, our alternative learning scheme is to erase already activated area, and allow the CNN models to activate more area during training. The proposed scheme is implemented by keeping the pairwise consistency between the output of the erased image and its original one. In particular, a tailored loss is proposed to keep such pairwise consistency by leveraging category-relevance information. Experiments on Places365 show the significant improvements of our method with various CNNs. Our method shows an inferior result on the object-centric dataset, ImageNet, which experimentally indicates that it captures the unique characteristics of scenes.

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ICML Conference 2021 Conference Paper

The Implicit Bias for Adaptive Optimization Algorithms on Homogeneous Neural Networks

Bohan Wang
Qi Meng
Wei Chen 0034
Tie-Yan Liu

Despite their overwhelming capacity to overfit, deep neural networks trained by specific optimization algorithms tend to generalize relatively well to unseen data. Recently, researchers explained it by investigating the implicit bias of optimization algorithms. A remarkable progress is the work (Lyu & Li, 2019), which proves gradient descent (GD) maximizes the margin of homogeneous deep neural networks. Except the first-order optimization algorithms like GD, adaptive algorithms such as AdaGrad, RMSProp and Adam are popular owing to their rapid training process. Mean-while, numerous works have provided empirical evidence that adaptive methods may suffer from poor generalization performance. However, theoretical explanation for the generalization of adaptive optimization algorithms is still lacking. In this paper, we study the implicit bias of adaptive optimization algorithms on homogeneous neural networks. In particular, we study the convergent direction of parameters when they are optimizing the logistic loss. We prove that the convergent direction of Adam and RMSProp is the same as GD, while for AdaGrad, the convergent direction depends on the adaptive conditioner. Technically, we provide a unified framework to analyze convergent direction of adaptive optimization algorithms by constructing novel and nontrivial adaptive gradient flow and surrogate margin. The theoretical findings explain the superiority on generalization of exponential moving average strategy that is adopted by RMSProp and Adam. To the best of knowledge, it is the first work to study the convergent direction of adaptive optimizations on non-linear deep neural networks

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UAI Conference 2021 Conference Paper

Tighter Generalization Bounds for Iterative Differentially Private Learning Algorithms

Fengxiang He
Bohan Wang
Dacheng Tao

This paper studies the relationship between generalization and privacy preservation of machine learning in two steps. We first establish an alignment between the two facets for any learning algorithm. We prove that $(\varepsilon, \delta)$-differential privacy implies an on-average generalization bound for a multi-sample-set learning algorithm, which further leads to a high-probability bound for any learning algorithm. We then investigate how the iterative nature shared by most learning algorithms influences privacy preservation and further generalization. Three composition theorems are proved to approximate the differential privacy of an iterative algorithm through the differential privacy of its every iteration. Integrating the above two steps, we eventually deliver generalization bounds for iterative learning algorithms. Our results are strictly tighter than the existing works. Particularly, our generalization bounds do not rely on the model size which is prohibitively large in deep learning. Experiments of MLP, VGG, and ResNet on MNIST, CIFAR-10, and CIFAR-100 are in full agreement with our theory. The theory applies to a wide spectrum of learning algorithms. In this paper, it is applied to the Gaussian mechanism as an example.

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ICLR Conference 2020 Conference Paper

Piecewise linear activations substantially shape the loss surfaces of neural networks

Fengxiang He
Bohan Wang
Dacheng Tao

Understanding the loss surface of a neural network is fundamentally important to the understanding of deep learning. This paper presents how piecewise linear activation functions substantially shape the loss surfaces of neural networks. We first prove that {\it the loss surfaces of many neural networks have infinite spurious local minima} which are defined as the local minima with higher empirical risks than the global minima. Our result demonstrates that the networks with piecewise linear activations possess substantial differences to the well-studied linear neural networks. This result holds for any neural network with arbitrary depth and arbitrary piecewise linear activation functions (excluding linear functions) under most loss functions in practice. Essentially, the underlying assumptions are consistent with most practical circumstances where the output layer is narrower than any hidden layer. In addition, the loss surface of a neural network with piecewise linear activations is partitioned into multiple smooth and multilinear cells by nondifferentiable boundaries. The constructed spurious local minima are concentrated in one cell as a valley: they are connected with each other by a continuous path, on which empirical risk is invariant. Further for one-hidden-layer networks, we prove that all local minima in a cell constitute an equivalence class; they are concentrated in a valley; and they are all global minima in the cell.

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