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Qianxiao Li

27 accepted papers

2026

The Effect of Attention Head Count on Transformer Approximation

ICLR 2026poster

Transformer has become the dominant architecture for sequence modeling, yet a detailed understanding of how its structural parameters influence expressive power remains limited. In this work, we study the approximation properties of transformers, with particular emphasis on the role of the number of…

Cited by 0SourceScholar
2025

A unified framework for establishing the universal approximation of transformer-type architectures

NeurIPS 2025poster

We investigate the universal approximation property (UAP) of transformer-type architectures, providing a unified theoretical framework that extends prior results on residual networks to models incorporating attention mechanisms. Our work identifies token distinguishability as a fundamental requireme…

Cited by 0SourceScholar
2025

Autocorrelation Matters: Understanding the Role of Initialization Schemes for State Space Models

ICLR 2025poster

Current methods for initializing state space model (SSM) parameters primarily rely on the HiPPO framework \citep{gu2023how}, which is based on online function approximation with the SSM kernel basis. However, the HiPPO framework does not explicitly account for the effects of the temporal structures…

Cited by 0SourcePDFScholar
2025

Continuity-Preserving Convolutional Autoencoders for Learning Continuous Latent Dynamical Models from Images

ICLR 2025poster

Continuous dynamical systems are cornerstones of many scientific and engineering disciplines. While machine learning offers powerful tools to model these systems from trajectory data, challenges arise when these trajectories are captured as images, resulting in pixel-level observations that are disc…

Cited by 0SourcePDFScholar
2025

From Weight-Based to State-Based Fine-Tuning: Further Memory Reduction on LoRA with Parallel Control

ICML 2025oral

The LoRA method has achieved notable success in reducing GPU memory usage by applying low-rank updates to weight matrices. Yet, one simple question remains: can we push this reduction even further? Furthermore, is it possible to achieve this while improving performance and reducing computation time?…

Cited by 0SourcePDFScholar
2024

An Optimal Control View of LoRA and Binary Controller Design for Vision Transformers

ECCV 2024poster

"While recent advancements in model fine-tuning predominantly emphasize the utilization of low-rank adaptation (LoRA), we propose an alternative approach centered on reducing the precision of adaptation matrices. In particular, we depart from the common viewpoint that considers adaptation matrices s…

Cited by 0SourcePDFScholar
2024

Inverse Approximation Theory for Nonlinear Recurrent Neural Networks

ICLR 2024spotlight

We prove an inverse approximation theorem for the approximation of nonlinear sequence-to-sequence relationships using recurrent neural networks (RNNs). This is a so-called Bernstein-type result in approximation theory, which deduces properties of a target function under the assumption that it can be…

2024

StableSSM: Alleviating the Curse of Memory in State-space Models through Stable Reparameterization

ICML 2024poster

In this paper, we investigate the long-term memory learning capabilities of state-space models (SSMs) from the perspective of parameterization. We prove that state-space models without any reparameterization exhibit a memory limitation similar to that of traditional RNNs: the target relationships th…

Cited by 9SourcePDFScholar
2022

On the approximation properties of recurrent encoder-decoder architectures

ICLR 2022spotlight

Encoder-decoder architectures have recently gained popularity in sequence to sequence modelling, featuring in state-of-the-art models such as transformers. However, a mathematical understanding of their working principles still remains limited. In this paper, we study the approximation properties of…

Cited by 7SourcePDFScholar
2021

Amata: An Annealing Mechanism for Adversarial Training Acceleration

AAAI 2021technical

Despite the empirical success in various domains, it has been revealed that deep neural networks are vulnerable to maliciously perturbed input data that much degrade their performance. This is known as adversarial attacks. To counter adversarial attacks, adversarial training formulated as a form of…

2021

Approximation Theory of Convolutional Architectures for Time Series Modelling

ICML 2021spotlight

We study the approximation properties of convolutional architectures applied to time series modelling, which can be formulated mathematically as a functional approximation problem. In the recurrent setting, recent results reveal an intricate connection between approximation efficiency and memory str…

Cited by 13SourcePDFScholar
2021

On the Curse of Memory in Recurrent Neural Networks: Approximation and Optimization Analysis

ICLR 2021poster

We study the approximation properties and optimization dynamics of recurrent neural networks (RNNs) when applied to learn input-output relationships in temporal data. We consider the simple but representative setting of using continuous-time linear RNNs to learn from data generated by linear relatio…

Cited by 43SourcePDFScholar
2019

A Quantitative Analysis of the Effect of Batch Normalization on Gradient Descent

ICML 2019oral

Despite its empirical success and recent theoretical progress, there generally lacks a quantitative analysis of the effect of batch normalization (BN) on the convergence and stability of gradient descent. In this paper, we provide such an analysis on the simple problem of ordinary least squares (OLS…

Cited by 43SourcePDFScholar
2018

An Optimal Control Approach to Deep Learning and Applications to Discrete-Weight Neural Networks

ICML 2018oral

Deep learning is formulated as a discrete-time optimal control problem. This allows one to characterize necessary conditions for optimality and develop training algorithms that do not rely on gradients with respect to the trainable parameters. In particular, we introduce the discrete-time method of…